Merge pull request #4 from hannesschulze/3-calculator

Add a calculator to the launcher

17 files changed, 2538 insertions, 152 deletions

diff --git a/src/application.c b/src/application.c
index a32e1ce..bad62b1 100644
--- a/src/application.c
+++ b/src/application.c
@@ -7,6 +7,7 @@
 #include "services/battery-service.h"
 #include "services/clock-service.h"
 #include "services/brightness-service.h"
+#include "services/quick-answer-service.h"
 #include "services/workspace-service.h"
 #include "services/notification-service.h"
 #include "services/audio-service.h"
@@ -38,6 +39,7 @@ struct _FoobarApplication
 	FoobarNetworkService*       network_service;
 	FoobarBluetoothService*     bluetooth_service;
 	FoobarApplicationService*   application_service;
+	FoobarQuickAnswerService*   quick_answer_service;
 	FoobarConfigurationService* configuration_service;
 	gulong                      config_handler_id;
 	FoobarServer*               server_skeleton;
@@ -180,6 +182,7 @@ void foobar_application_activate( GApplication* app )
 	self->network_service = foobar_network_service_new( );
 	self->bluetooth_service = foobar_bluetooth_service_new( );
 	self->application_service = foobar_application_service_new( );
+	self->quick_answer_service = foobar_quick_answer_service_new( );
 	self->configuration_service = foobar_configuration_service_new( );
 
 	// Enforce a uniform style by forcing Adwaita and shipping our own icons.
@@ -231,6 +234,7 @@ void foobar_application_activate( GApplication* app )
 
 	self->launcher = foobar_launcher_new(
 		self->application_service,
+		self->quick_answer_service,
 		self->configuration_service );
 	g_object_ref( self->launcher );
 
@@ -358,6 +362,7 @@ void foobar_application_finalize( GObject* object )
 	g_clear_object( &self->network_service );
 	g_clear_object( &self->bluetooth_service );
 	g_clear_object( &self->application_service );
+	g_clear_object( &self->quick_answer_service );
 	g_clear_object( &self->configuration_service );
 	g_clear_object( &self->style_provider );
 	g_clear_object( &self->server_skeleton );
diff --git a/src/launcher-item.c b/src/launcher-item.c
new file mode 100644
index 0000000..c4de70b
--- /dev/null
+++ b/src/launcher-item.c
@@ -0,0 +1,73 @@
+#include "launcher-item.h"
+
+static void foobar_launcher_item_default_init( FoobarLauncherItemInterface* iface );
+
+G_DEFINE_INTERFACE( FoobarLauncherItem, foobar_launcher_item, G_TYPE_OBJECT )
+
+//
+// Static initialization for the launcher item interface.
+//
+void foobar_launcher_item_default_init( FoobarLauncherItemInterface* iface )
+{
+	g_object_interface_install_property( iface, g_param_spec_string(
+		"title",
+		"Title",
+		"The title text displayed in the launcher.",
+		NULL,
+		G_PARAM_READABLE ) );
+	g_object_interface_install_property( iface, g_param_spec_string(
+		"description",
+		"Description",
+		"Text displayed below the title.",
+		NULL,
+		G_PARAM_READABLE ) );
+	g_object_interface_install_property( iface, g_param_spec_object(
+		"icon",
+		"Icon",
+		"Icon to show for the item.",
+		G_TYPE_ICON,
+		G_PARAM_READABLE ) );
+}
+
+//
+// Get the title text displayed in the launcher.
+//
+gchar const* foobar_launcher_item_get_title( FoobarLauncherItem* self )
+{
+	g_return_val_if_fail( FOOBAR_IS_LAUNCHER_ITEM( self ), NULL );
+	FoobarLauncherItemInterface* iface = FOOBAR_LAUNCHER_ITEM_GET_IFACE( self );
+	g_return_val_if_fail( iface->get_title != NULL, NULL );
+	return iface->get_title( self );
+}
+
+//
+// Get the text displayed below the title.
+//
+gchar const* foobar_launcher_item_get_description( FoobarLauncherItem* self )
+{
+	g_return_val_if_fail( FOOBAR_IS_LAUNCHER_ITEM( self ), NULL );
+	FoobarLauncherItemInterface* iface = FOOBAR_LAUNCHER_ITEM_GET_IFACE( self );
+	g_return_val_if_fail( iface->get_description != NULL, NULL );
+	return iface->get_description( self );
+}
+
+//
+// Get the icon to show for the item.
+//
+GIcon* foobar_launcher_item_get_icon( FoobarLauncherItem* self )
+{
+	g_return_val_if_fail( FOOBAR_IS_LAUNCHER_ITEM( self ), NULL );
+	FoobarLauncherItemInterface* iface = FOOBAR_LAUNCHER_ITEM_GET_IFACE( self );
+	g_return_val_if_fail( iface->get_icon != NULL, NULL );
+	return iface->get_icon( self );
+}
+
+//
+// Activate the item, e.g. by launching the application.
+//
+void foobar_launcher_item_activate( FoobarLauncherItem* self )
+{
+	g_return_if_fail( FOOBAR_IS_LAUNCHER_ITEM( self ) );
+	FoobarLauncherItemInterface* iface = FOOBAR_LAUNCHER_ITEM_GET_IFACE( self );
+	if ( iface->activate ) { iface->activate( self ); }
+}
diff --git a/src/launcher-item.h b/src/launcher-item.h
new file mode 100644
index 0000000..b2d274a
--- /dev/null
+++ b/src/launcher-item.h
@@ -0,0 +1,28 @@
+#pragma once
+
+#include <glib-object.h>
+#include <gio/gio.h>
+
+G_BEGIN_DECLS
+
+#define FOOBAR_TYPE_LAUNCHER_ITEM foobar_launcher_item_get_type( )
+
+G_DECLARE_INTERFACE( FoobarLauncherItem, foobar_launcher_item, FOOBAR, LAUNCHER_ITEM, GObject )
+
+struct _FoobarLauncherItemInterface
+{
+	GTypeInterface parent_interface;
+
+	gchar const* ( *get_title )      ( FoobarLauncherItem* self );
+	gchar const* ( *get_description )( FoobarLauncherItem* self );
+	GIcon*       ( *get_icon )       ( FoobarLauncherItem* self );
+	void         ( *activate )       ( FoobarLauncherItem* self );
+};
+
+gchar const* foobar_launcher_item_get_title      ( FoobarLauncherItem* self );
+gchar const* foobar_launcher_item_get_description( FoobarLauncherItem* self );
+GIcon*       foobar_launcher_item_get_icon       ( FoobarLauncherItem* self );
+void         foobar_launcher_item_activate       ( FoobarLauncherItem* self );
+
+G_END_DECLS
+
diff --git a/src/launcher.c b/src/launcher.c
index da37715..f4b34d8 100644
--- a/src/launcher.c
+++ b/src/launcher.c
@@ -1,4 +1,5 @@
 #include "launcher.h"
+#include "launcher-item.h"
 #include "widgets/limit-container.h"
 #include <gtk4-layer-shell.h>
 #include <gdk/gdkkeysyms.h>
@@ -21,8 +22,11 @@ struct _FoobarLauncher
 	GtkWidget*                  list_view;
 	GtkWidget*                  limit_container;
 	GtkFilterListModel*         filter_model;
+	GListStore*                 quick_answer_model;
+	GtkFlattenListModel*        flatten_model;
 	GtkSingleSelection*         selection_model;
 	FoobarApplicationService*   application_service;
+	FoobarQuickAnswerService*   quick_answer_service;
 	FoobarConfigurationService* configuration_service;
 	gulong                      config_handler_id;
 };
@@ -119,9 +123,28 @@ void foobar_launcher_init( FoobarLauncher* self )
 
 	GtkWidget *separator = gtk_separator_new( GTK_ORIENTATION_HORIZONTAL );
 
+	// Set up the results list view and an event controller for auto-switching focus to the input.
+
+	GtkListItemFactory* item_factory = gtk_signal_list_item_factory_new( );
+	g_signal_connect( item_factory, "setup", G_CALLBACK( foobar_launcher_handle_item_setup ), NULL );
+
+	GtkCustomFilter* filter = gtk_custom_filter_new( foobar_launcher_filter_func, self, NULL );
+
+	self->filter_model = gtk_filter_list_model_new( NULL, GTK_FILTER( filter ) );
+
+	self->quick_answer_model = g_list_store_new( FOOBAR_TYPE_LAUNCHER_ITEM );
+
+	GListStore* flattened_models = g_list_store_new( G_TYPE_LIST_MODEL );
+	g_list_store_append( flattened_models, self->quick_answer_model );
+	g_list_store_append( flattened_models, self->filter_model );
+
+	self->flatten_model = gtk_flatten_list_model_new( G_LIST_MODEL( flattened_models ) );
+
+	self->selection_model = gtk_single_selection_new( G_LIST_MODEL( g_object_ref( self->flatten_model ) ) );
+
 	{
-		GtkExpression* list_expr = gtk_constant_expression_new( GTK_TYPE_FILTER_LIST_MODEL, self->filter_model );
-		GtkExpression* count_expr = gtk_property_expression_new( GTK_TYPE_FILTER_LIST_MODEL, list_expr, "n-items" );
+		GtkExpression* list_expr = gtk_constant_expression_new( GTK_TYPE_FLATTEN_LIST_MODEL, self->flatten_model );
+		GtkExpression* count_expr = gtk_property_expression_new( GTK_TYPE_FLATTEN_LIST_MODEL, list_expr, "n-items" );
 		GtkExpression* visible_params[] = { count_expr };
 		GtkExpression* visible_expr = gtk_cclosure_expression_new(
 			G_TYPE_BOOLEAN,
@@ -134,17 +157,6 @@ void foobar_launcher_init( FoobarLauncher* self )
 		gtk_expression_bind( visible_expr, separator, "visible", NULL );
 	}
 
-	// Set up the results list view and an event controller for auto-switching focus to the input.
-
-	GtkListItemFactory* item_factory = gtk_signal_list_item_factory_new( );
-	g_signal_connect( item_factory, "setup", G_CALLBACK( foobar_launcher_handle_item_setup ), NULL );
-
-	GtkCustomFilter* filter = gtk_custom_filter_new( foobar_launcher_filter_func, self, NULL );
-
-	self->filter_model = gtk_filter_list_model_new( NULL, GTK_FILTER( filter ) );
-
-	self->selection_model = gtk_single_selection_new( G_LIST_MODEL( g_object_ref( self->filter_model ) ) );
-
 	GtkEventController* list_controller = gtk_event_controller_key_new( );
 	g_signal_connect( list_controller, "key-pressed", G_CALLBACK( foobar_launcher_handle_list_key ), self );
 	g_signal_connect( list_controller, "key-released", G_CALLBACK( foobar_launcher_handle_list_key ), self );
@@ -201,8 +213,11 @@ void foobar_launcher_finalize( GObject* object )
 
 	g_clear_signal_handler( &self->config_handler_id, self->configuration_service );
 	g_clear_object( &self->filter_model );
+	g_clear_object( &self->quick_answer_model );
+	g_clear_object( &self->flatten_model );
 	g_clear_object( &self->selection_model );
 	g_clear_object( &self->application_service );
+	g_clear_object( &self->quick_answer_service );
 	g_clear_object( &self->configuration_service );
 	g_clear_pointer( &self->search_terms, g_strfreev );
 
@@ -218,13 +233,16 @@ void foobar_launcher_finalize( GObject* object )
 //
 FoobarLauncher* foobar_launcher_new(
 	FoobarApplicationService*   application_service,
+	FoobarQuickAnswerService*   quick_answer_service,
 	FoobarConfigurationService* configuration_service )
 {
 	g_return_val_if_fail( FOOBAR_IS_APPLICATION_SERVICE( application_service ), NULL );
+	g_return_val_if_fail( FOOBAR_IS_QUICK_ANSWER_SERVICE( quick_answer_service ), NULL );
 	g_return_val_if_fail( FOOBAR_IS_CONFIGURATION_SERVICE( configuration_service ), NULL );
 
 	FoobarLauncher* self = g_object_new( FOOBAR_TYPE_LAUNCHER, NULL );
 	self->application_service = g_object_ref( application_service );
+	self->quick_answer_service = g_object_ref( quick_answer_service );
 	self->configuration_service = g_object_ref( configuration_service );
 
 	// Set up the result list view's source model.
@@ -299,6 +317,17 @@ void foobar_launcher_handle_search_changed(
 {
 	FoobarLauncher* self = (FoobarLauncher*)userdata;
 
+	// Update quick answer.
+
+	g_autoptr(FoobarQuickAnswer) answer = foobar_quick_answer_service_query( self->quick_answer_service, gtk_editable_get_text( editable ) );
+	g_list_store_remove_all( self->quick_answer_model );
+	if (answer)
+	{
+		g_list_store_append(self->quick_answer_model, answer);
+	}
+
+	// Update filter.
+
 	GStrvBuilder* terms_builder = g_strv_builder_new( );
 	g_autofree gchar* query = g_strdup( gtk_editable_get_text( editable ) );
 	gchar* query_start = query;
@@ -416,24 +445,24 @@ void foobar_launcher_handle_item_setup(
 	gtk_widget_set_valign( icon, GTK_ALIGN_CENTER );
 	gtk_widget_add_css_class( icon, "icon" );
 
-	GtkWidget* name = gtk_label_new( NULL );
-	gtk_label_set_justify( GTK_LABEL( name ), GTK_JUSTIFY_LEFT );
-	gtk_label_set_xalign( GTK_LABEL( name ), 0 );
-	gtk_label_set_wrap( GTK_LABEL( name ), FALSE );
-	gtk_label_set_ellipsize( GTK_LABEL( name ), PANGO_ELLIPSIZE_END );
-	gtk_widget_add_css_class( name, "name" );
+	GtkWidget* title = gtk_label_new( NULL );
+	gtk_label_set_justify( GTK_LABEL( title ), GTK_JUSTIFY_LEFT );
+	gtk_label_set_xalign( GTK_LABEL( title ), 0 );
+	gtk_label_set_wrap( GTK_LABEL( title ), FALSE );
+	gtk_label_set_ellipsize( GTK_LABEL( title ), PANGO_ELLIPSIZE_END );
+	gtk_widget_add_css_class( title, "name" );
 
 	GtkWidget* description = gtk_label_new( NULL );
 	gtk_label_set_justify( GTK_LABEL( description ), GTK_JUSTIFY_LEFT );
 	gtk_label_set_xalign( GTK_LABEL( description ), 0 );
-	gtk_label_set_wrap( GTK_LABEL( name ), FALSE );
+	gtk_label_set_wrap( GTK_LABEL( description ), FALSE );
 	gtk_label_set_ellipsize( GTK_LABEL( description ), PANGO_ELLIPSIZE_END );
 	gtk_widget_add_css_class( description, "description" );
 
 	GtkWidget* column = gtk_box_new( GTK_ORIENTATION_VERTICAL, 0 );
 	gtk_widget_set_hexpand( column, TRUE );
 	gtk_widget_set_valign( column, GTK_ALIGN_CENTER );
-	gtk_box_append( GTK_BOX( column ), name );
+	gtk_box_append( GTK_BOX( column ), title );
 	gtk_box_append( GTK_BOX( column ), description );
 
 	GtkWidget* row = gtk_box_new( GTK_ORIENTATION_HORIZONTAL, 0 );
@@ -447,7 +476,7 @@ void foobar_launcher_handle_item_setup(
 
 	{
 		GtkExpression* item_expr = gtk_property_expression_new( GTK_TYPE_LIST_ITEM, NULL, "item" );
-		GtkExpression* icon_expr = gtk_property_expression_new( FOOBAR_TYPE_APPLICATION_ITEM, item_expr, "icon" );
+		GtkExpression* icon_expr = gtk_property_expression_new( FOOBAR_TYPE_LAUNCHER_ITEM, item_expr, "icon" );
 		gtk_expression_bind( gtk_expression_ref( icon_expr ), icon, "gicon", list_item );
 		GtkExpression* visible_params[] = { icon_expr };
 		GtkExpression* visible_expr = gtk_cclosure_expression_new(
@@ -463,13 +492,13 @@ void foobar_launcher_handle_item_setup(
 
 	{
 		GtkExpression* item_expr = gtk_property_expression_new( GTK_TYPE_LIST_ITEM, NULL, "item" );
-		GtkExpression* name_expr = gtk_property_expression_new( FOOBAR_TYPE_APPLICATION_ITEM, item_expr, "name" );
-		gtk_expression_bind( name_expr, name, "label", list_item );
+		GtkExpression* title_expr = gtk_property_expression_new( FOOBAR_TYPE_LAUNCHER_ITEM, item_expr, "title" );
+		gtk_expression_bind( title_expr, title, "label", list_item );
 	}
 
 	{
 		GtkExpression* item_expr = gtk_property_expression_new( GTK_TYPE_LIST_ITEM, NULL, "item" );
-		GtkExpression* description_expr = gtk_property_expression_new( FOOBAR_TYPE_APPLICATION_ITEM, item_expr, "description" );
+		GtkExpression* description_expr = gtk_property_expression_new( FOOBAR_TYPE_LAUNCHER_ITEM, item_expr, "description" );
 		gtk_expression_bind( gtk_expression_ref( description_expr ), description, "label", list_item );
 		GtkExpression* visible_params[] = { description_expr };
 		GtkExpression* visible_expr = gtk_cclosure_expression_new(
@@ -496,8 +525,8 @@ void foobar_launcher_handle_item_activate(
 	FoobarLauncher* self = (FoobarLauncher*)userdata;
 
 	GListModel* list = G_LIST_MODEL( gtk_list_view_get_model( view ) );
-	FoobarApplicationItem* item = g_list_model_get_item( list, position );
-	foobar_application_item_launch( item );
+	FoobarLauncherItem* item = g_list_model_get_item( list, position );
+	foobar_launcher_item_activate( item );
 	gtk_widget_set_visible( GTK_WIDGET( self ), FALSE );
 }
 
diff --git a/src/launcher.h b/src/launcher.h
index 4c3e495..5d92607 100644
--- a/src/launcher.h
+++ b/src/launcher.h
@@ -3,6 +3,7 @@
 #include <gtk/gtk.h>
 #include "services/application-service.h"
 #include "services/configuration-service.h"
+#include "services/quick-answer-service.h"
 
 G_BEGIN_DECLS
 
@@ -11,6 +12,7 @@ G_BEGIN_DECLS
 G_DECLARE_FINAL_TYPE( FoobarLauncher, foobar_launcher, FOOBAR, LAUNCHER, GtkWindow )
 
 FoobarLauncher* foobar_launcher_new                ( FoobarApplicationService*          application_service,
+													 FoobarQuickAnswerService*          quick_answer_service,
                                                      FoobarConfigurationService*        configuration_service );
 void            foobar_launcher_apply_configuration( FoobarLauncher*                    self,
                                                      FoobarLauncherConfiguration const* config );
diff --git a/src/meson.build b/src/meson.build
index b089bce..b9383fb 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -1,41 +1,74 @@
 foobar_sources = files(
-  'main.c',
   'application.c',
   'utils.c',
   'panel.c',
   'launcher.c',
+  'launcher-item.c',
   'control-center.c',
   'notification-area.c',
 )
+foobar_tests = {}
 
 subdir('dbus')
 subdir('services')
 subdir('widgets')
 
+c_args = [
+  '-Wall',
+  '-Werror',
+  '-Wswitch-enum',
+  '-Wswitch-default',
+  '-Wunused',
+  '-Wuninitialized',
+]
+
+deps = [
+  glib_dep,
+  gio_dep,
+  gio_unix_dep,
+  gtk_dep,
+  json_dep,
+  gmp_dep,
+  nm_dep,
+  m_dep,
+  layershell_dep,
+  gvc_dep,
+]
+
+libfoobar = static_library(
+  meson.project_name(),
+  foobar_sources,
+  include_directories: include_directories('.'),
+  dependencies: deps,
+  install: false,
+  c_args: c_args
+)
+
+libfoobar_dep = declare_dependency(
+  link_with: libfoobar,
+  include_directories: include_directories('.'),
+  dependencies: deps,
+)
+
 executable(
   meson.project_name(),
+  'main.c',
   styles_resource,
   icons_resource,
-  foobar_sources,
-  include_directories: include_directories('.'),
-  dependencies: [
-    glib_dep,
-    gio_dep,
-    gio_unix_dep,
-    gtk_dep,
-    json_dep,
-    nm_dep,
-    m_dep,
-    layershell_dep,
-    gvc_dep,
-  ],
+  dependencies: [ libfoobar_dep ],
   install: true,
-  c_args: [
-    '-Wall',
-    '-Werror',
-    '-Wswitch-enum',
-    '-Wswitch-default',
-    '-Wunused',
-    '-Wuninitialized',
-  ],
+  c_args: c_args
 )
+
+if mutest_dep.found()
+  foreach name, sources : foobar_tests
+    test(
+      name,
+      executable(
+        'foobar-test-' + name,
+        sources,
+        dependencies: [ libfoobar_dep, mutest_dep ],
+      ),
+    )
+  endforeach
+endif
diff --git a/src/services/application-service.c b/src/services/application-service.c
index 3885719..42835ac 100644
--- a/src/services/application-service.c
+++ b/src/services/application-service.c
@@ -1,4 +1,5 @@
 #include "services/application-service.h"
+#include "launcher-item.h"
 #include "utils.h"
 #include <gtk/gtk.h>
 #include <gio/gdesktopappinfo.h>
@@ -21,29 +22,38 @@ struct _FoobarApplicationItem
 enum
 {
 	APP_PROP_ID = 1,
-	APP_PROP_NAME,
-	APP_PROP_DESCRIPTION,
 	APP_PROP_EXECUTABLE,
 	APP_PROP_CATEGORIES,
-	APP_PROP_ICON,
 	APP_PROP_FREQUENCY,
+	APP_PROP_TITLE,
+	APP_PROP_DESCRIPTION,
+	APP_PROP_ICON,
 	N_APP_PROPS,
 };
 
 static GParamSpec* app_props[N_APP_PROPS] = { 0 };
 
-static void                   foobar_application_item_class_init  ( FoobarApplicationItemClass* klass );
-static void                   foobar_application_item_init        ( FoobarApplicationItem*      self );
-static void                   foobar_application_item_get_property( GObject*                    object,
-                                                                    guint                       prop_id,
-                                                                    GValue*                     value,
-                                                                    GParamSpec*                 pspec );
-static void                   foobar_application_item_finalize    ( GObject*                    object );
-static FoobarApplicationItem* foobar_application_item_new         ( FoobarApplicationService*   service );
-static void                   foobar_application_item_set_info    ( FoobarApplicationItem*      self,
-                                                                    GAppInfo*                   value );
+static void                   foobar_application_item_class_init                  ( FoobarApplicationItemClass* klass );
+static void                   foobar_application_item_launcher_item_interface_init( FoobarLauncherItemInterface* iface );
+static void                   foobar_application_item_init                        ( FoobarApplicationItem*      self );
+static void                   foobar_application_item_get_property                ( GObject*                    object,
+                                                                                    guint                       prop_id,
+                                                                                    GValue*                     value,
+                                                                                    GParamSpec*                 pspec );
+static void                   foobar_application_item_finalize                    ( GObject*                    object );
+static FoobarApplicationItem* foobar_application_item_new                         ( FoobarApplicationService*   service );
+static gchar const*           foobar_application_item_get_title                   ( FoobarLauncherItem*         self );
+static gchar const*           foobar_application_item_get_description             ( FoobarLauncherItem*         self );
+static GIcon*                 foobar_application_item_get_icon                    ( FoobarLauncherItem*         self );
+static void                   foobar_application_item_activate                    ( FoobarLauncherItem*         self );
+static void                   foobar_application_item_set_info                    ( FoobarApplicationItem*      self,
+                                                                                    GAppInfo*                   value );
 
-G_DEFINE_FINAL_TYPE( FoobarApplicationItem, foobar_application_item, G_TYPE_OBJECT )
+G_DEFINE_FINAL_TYPE_WITH_CODE(
+	FoobarApplicationItem,
+	foobar_application_item,
+	G_TYPE_OBJECT,
+	G_IMPLEMENT_INTERFACE( FOOBAR_TYPE_LAUNCHER_ITEM, foobar_application_item_launcher_item_interface_init ) )
 
 //
 // FoobarApplicationService:
@@ -124,24 +134,13 @@ void foobar_application_item_class_init( FoobarApplicationItemClass* klass )
 	object_klass->get_property = foobar_application_item_get_property;
 	object_klass->finalize = foobar_application_item_finalize;
 
+	gpointer launcher_item_iface = g_type_default_interface_peek( FOOBAR_TYPE_LAUNCHER_ITEM );
 	app_props[APP_PROP_ID] = g_param_spec_string(
 		"id",
 		"ID",
 		"Application identifier string.",
 		NULL,
 		G_PARAM_READABLE );
-	app_props[APP_PROP_NAME] = g_param_spec_string(
-		"name",
-		"Name",
-		"Displayed name for the application.",
-		NULL,
-		G_PARAM_READABLE );
-	app_props[APP_PROP_DESCRIPTION] = g_param_spec_string(
-		"description",
-		"Description",
-		"Brief description of the application.",
-		NULL,
-		G_PARAM_READABLE );
 	app_props[APP_PROP_EXECUTABLE] = g_param_spec_string(
 		"executable",
 		"Executable",
@@ -154,12 +153,6 @@ void foobar_application_item_class_init( FoobarApplicationItemClass* klass )
 		"Semicolon-separated list of application categories.",
 		NULL,
 		G_PARAM_READABLE );
-	app_props[APP_PROP_ICON] = g_param_spec_object(
-		"icon",
-		"Icon",
-		"Icon to show for the application.",
-		G_TYPE_ICON,
-		G_PARAM_READABLE );
 	app_props[APP_PROP_FREQUENCY] = g_param_spec_int64(
 		"frequency",
 		"Frequency",
@@ -168,10 +161,30 @@ void foobar_application_item_class_init( FoobarApplicationItemClass* klass )
 		INT64_MAX,
 		0,
 		G_PARAM_READABLE );
+	app_props[APP_PROP_TITLE] = g_param_spec_override(
+		"title",
+		g_object_interface_find_property( launcher_item_iface, "title" ) );
+	app_props[APP_PROP_DESCRIPTION] = g_param_spec_override(
+		"description",
+		g_object_interface_find_property( launcher_item_iface, "description" ) );
+	app_props[APP_PROP_ICON] = g_param_spec_override(
+		"icon",
+		g_object_interface_find_property( launcher_item_iface, "icon" ) );
 	g_object_class_install_properties( object_klass, N_APP_PROPS, app_props );
 }
 
 //
+// Static initialization of the FoobarLauncherItem interface.
+//
+void foobar_application_item_launcher_item_interface_init( FoobarLauncherItemInterface* iface )
+{
+	iface->get_title = foobar_application_item_get_title;
+	iface->get_description = foobar_application_item_get_description;
+	iface->get_icon = foobar_application_item_get_icon;
+	iface->activate = foobar_application_item_activate;
+}
+
+//
 // Instance initialization for application items.
 //
 void foobar_application_item_init( FoobarApplicationItem* self )
@@ -195,24 +208,24 @@ void foobar_application_item_get_property(
 		case APP_PROP_ID:
 			g_value_set_string( value, foobar_application_item_get_id( self ) );
 			break;
-		case APP_PROP_NAME:
-			g_value_set_string( value, foobar_application_item_get_name( self ) );
-			break;
-		case APP_PROP_DESCRIPTION:
-			g_value_set_string( value, foobar_application_item_get_description( self ) );
-			break;
 		case APP_PROP_EXECUTABLE:
 			g_value_set_string( value, foobar_application_item_get_executable( self ) );
 			break;
 		case APP_PROP_CATEGORIES:
 			g_value_set_string( value, foobar_application_item_get_categories( self ) );
 			break;
-		case APP_PROP_ICON:
-			g_value_set_object( value, foobar_application_item_get_icon( self ) );
-			break;
 		case APP_PROP_FREQUENCY:
 			g_value_set_int64( value, foobar_application_item_get_frequency( self ) );
 			break;
+		case APP_PROP_TITLE:
+			g_value_set_string( value, foobar_launcher_item_get_title( FOOBAR_LAUNCHER_ITEM ( self ) ) );
+			break;
+		case APP_PROP_DESCRIPTION:
+			g_value_set_string( value, foobar_launcher_item_get_description( FOOBAR_LAUNCHER_ITEM( self ) ) );
+			break;
+		case APP_PROP_ICON:
+			g_value_set_object( value, foobar_launcher_item_get_icon( FOOBAR_LAUNCHER_ITEM( self ) ) );
+			break;
 		default:
 			G_OBJECT_WARN_INVALID_PROPERTY_ID( object, prop_id, pspec );
 			break;
@@ -251,62 +264,91 @@ gchar const* foobar_application_item_get_id( FoobarApplicationItem* self )
 }
 
 //
-// Get the application's human-readable name.
+// Get the application's executable name.
 //
-gchar const* foobar_application_item_get_name( FoobarApplicationItem* self )
+gchar const* foobar_application_item_get_executable( FoobarApplicationItem* self )
 {
 	g_return_val_if_fail( FOOBAR_IS_APPLICATION_ITEM( self ), NULL );
-	return self->info ? g_app_info_get_display_name( self->info ) : NULL;
+	return self->info ? g_app_info_get_executable( self->info ) : NULL;
 }
 
 //
-// Get an optional short description for the application.
+// Get the semicolon-separated list of categories for this application.
 //
-gchar const* foobar_application_item_get_description( FoobarApplicationItem* self )
+gchar const* foobar_application_item_get_categories( FoobarApplicationItem* self )
 {
 	g_return_val_if_fail( FOOBAR_IS_APPLICATION_ITEM( self ), NULL );
-	return self->info ? g_app_info_get_description( self->info ) : NULL;
+	return G_IS_DESKTOP_APP_INFO( self->info )
+		? g_desktop_app_info_get_categories( G_DESKTOP_APP_INFO( self->info ) )
+		: NULL;
 }
 
 //
-// Get the application's executable name.
+// Get the number of times this application was opened using the launcher.
 //
-gchar const* foobar_application_item_get_executable( FoobarApplicationItem* self )
+gint64 foobar_application_item_get_frequency( FoobarApplicationItem* self )
 {
-	g_return_val_if_fail( FOOBAR_IS_APPLICATION_ITEM( self ), NULL );
-	return self->info ? g_app_info_get_executable( self->info ) : NULL;
+	g_return_val_if_fail( FOOBAR_IS_APPLICATION_ITEM( self ), 0 );
+
+	if ( !self->service ) { return 0; }
+	gpointer value = g_hash_table_lookup( self->service->frequencies, foobar_application_item_get_id( self ) );
+	return GPOINTER_TO_SIZE( value );
 }
 
 //
-// Get the semicolon-separated list of categories for this application.
+// Get the application's human-readable name.
 //
-gchar const* foobar_application_item_get_categories( FoobarApplicationItem* self )
+gchar const* foobar_application_item_get_title( FoobarLauncherItem* item )
 {
-	g_return_val_if_fail( FOOBAR_IS_APPLICATION_ITEM( self ), NULL );
-	return G_IS_DESKTOP_APP_INFO( self->info )
-		? g_desktop_app_info_get_categories( G_DESKTOP_APP_INFO( self->info ) )
-		: NULL;
+	FoobarApplicationItem* self = ( FoobarApplicationItem* )item;
+	return self->info ? g_app_info_get_display_name( self->info ) : NULL;
+}
+
+//
+// Get an optional short description for the application.
+//
+gchar const* foobar_application_item_get_description( FoobarLauncherItem* item )
+{
+	FoobarApplicationItem* self = ( FoobarApplicationItem* )item;
+	return self->info ? g_app_info_get_description( self->info ) : NULL;
 }
 
 //
 // Get an icon representing the application.
 //
-GIcon* foobar_application_item_get_icon( FoobarApplicationItem* self )
+GIcon* foobar_application_item_get_icon( FoobarLauncherItem* item )
 {
-	g_return_val_if_fail( FOOBAR_IS_APPLICATION_ITEM( self ), NULL );
+	FoobarApplicationItem* self = ( FoobarApplicationItem* )item;
 	return self->info ? g_app_info_get_icon( self->info ) : NULL;
 }
 
 //
-// Get the number of times this application was opened using the launcher.
+// Launch the application, increasing its frequency by one.
 //
-gint64 foobar_application_item_get_frequency( FoobarApplicationItem* self )
+void foobar_application_item_activate( FoobarLauncherItem* item )
 {
-	g_return_val_if_fail( FOOBAR_IS_APPLICATION_ITEM( self ), 0 );
+	FoobarApplicationItem* self = ( FoobarApplicationItem* )item;
 
-	if ( !self->service ) { return 0; }
-	gpointer value = g_hash_table_lookup( self->service->frequencies, foobar_application_item_get_id( self ) );
-	return GPOINTER_TO_SIZE( value );
+	if ( !self->info ) { return; }
+
+	g_autoptr( GError ) error = NULL;
+	if ( !g_app_info_launch( self->info, NULL, NULL, &error ) )
+	{
+		g_warning( "Unable to launch application: %s", error->message );
+	}
+
+	gchar const* id = foobar_application_item_get_id( self );
+	if ( !self->service || !id ) { return; }
+
+	gpointer value = g_hash_table_lookup( self->service->frequencies, id );
+	value = GSIZE_TO_POINTER( GPOINTER_TO_SIZE( value ) + 1 );
+	g_mutex_lock( &self->service->frequencies_mutex );
+	g_hash_table_insert( self->service->frequencies, g_strdup( id ), value );
+	g_mutex_unlock( &self->service->frequencies_mutex );
+
+	g_object_notify_by_pspec( G_OBJECT( self ), app_props[APP_PROP_FREQUENCY] );
+	gtk_sorter_changed( gtk_sort_list_model_get_sorter( self->service->sorted_items ), GTK_SORTER_CHANGE_DIFFERENT );
+	foobar_application_service_write_cache( self->service );
 }
 
 //
@@ -325,7 +367,7 @@ void foobar_application_item_set_info(
 		if ( value ) { self->info = g_object_ref( value ); }
 
 		g_object_notify_by_pspec( G_OBJECT( self ), app_props[APP_PROP_ID] );
-		g_object_notify_by_pspec( G_OBJECT( self ), app_props[APP_PROP_NAME] );
+		g_object_notify_by_pspec( G_OBJECT( self ), app_props[APP_PROP_TITLE] );
 		g_object_notify_by_pspec( G_OBJECT( self ), app_props[APP_PROP_DESCRIPTION] );
 		g_object_notify_by_pspec( G_OBJECT( self ), app_props[APP_PROP_EXECUTABLE] );
 		g_object_notify_by_pspec( G_OBJECT( self ), app_props[APP_PROP_ICON] );
@@ -346,8 +388,8 @@ gboolean foobar_application_item_match(
 	for ( gchar const* const* it = terms; *it; ++it )
 	{
 		gchar const* term = *it;
-		gchar const* name = foobar_application_item_get_name( self );
-		gchar const* description = foobar_application_item_get_description( self );
+		gchar const* name = foobar_launcher_item_get_title( FOOBAR_LAUNCHER_ITEM( self ) );
+		gchar const* description = foobar_launcher_item_get_description( FOOBAR_LAUNCHER_ITEM( self ) );
 		gchar const* executable = foobar_application_item_get_executable( self );
 		gchar const* categories = foobar_application_item_get_categories( self );
 		gchar const* id = foobar_application_item_get_id( self );
@@ -363,35 +405,6 @@ gboolean foobar_application_item_match(
 	return TRUE;
 }
 
-//
-// Launch the application, increasing its frequency by one.
-//
-void foobar_application_item_launch( FoobarApplicationItem* self )
-{
-	g_return_if_fail( FOOBAR_IS_APPLICATION_ITEM( self ) );
-
-	if ( !self->info ) { return; }
-
-	g_autoptr( GError ) error = NULL;
-	if ( !g_app_info_launch( self->info, NULL, NULL, &error ) )
-	{
-		g_warning( "Unable to launch application: %s", error->message );
-	}
-
-	gchar const* id = foobar_application_item_get_id( self );
-	if ( !self->service || !id ) { return; }
-
-	gpointer value = g_hash_table_lookup( self->service->frequencies, id );
-	value = GSIZE_TO_POINTER( GPOINTER_TO_SIZE( value ) + 1 );
-	g_mutex_lock( &self->service->frequencies_mutex );
-	g_hash_table_insert( self->service->frequencies, g_strdup( id ), value );
-	g_mutex_unlock( &self->service->frequencies_mutex );
-
-	g_object_notify_by_pspec( G_OBJECT( self ), app_props[APP_PROP_FREQUENCY] );
-	gtk_sorter_changed( gtk_sort_list_model_get_sorter( self->service->sorted_items ), GTK_SORTER_CHANGE_DIFFERENT );
-	foobar_application_service_write_cache( self->service );
-}
-
 // ---------------------------------------------------------------------------------------------------------------------
 // Service Implementation
 // ---------------------------------------------------------------------------------------------------------------------
@@ -722,8 +735,8 @@ gint foobar_application_service_sort_func(
 	if ( freq_a > freq_b ) { return -1; }
 	if ( freq_a < freq_b ) { return 1; }
 
-	gchar const* name_a = foobar_application_item_get_name( app_a );
-	gchar const* name_b = foobar_application_item_get_name( app_b );
+	gchar const* name_a = foobar_launcher_item_get_title( FOOBAR_LAUNCHER_ITEM( app_a ) );
+	gchar const* name_b = foobar_launcher_item_get_title( FOOBAR_LAUNCHER_ITEM( app_b ) );
 	gint name_res = g_strcmp0( name_a, name_b );
 	if ( name_res ) { return name_res; }
 
diff --git a/src/services/application-service.h b/src/services/application-service.h
index 3c2622a..dd043fc 100644
--- a/src/services/application-service.h
+++ b/src/services/application-service.h
@@ -11,15 +11,11 @@ G_BEGIN_DECLS
 G_DECLARE_FINAL_TYPE( FoobarApplicationItem, foobar_application_item, FOOBAR, APPLICATION_ITEM, GObject )
 
 gchar const* foobar_application_item_get_id         ( FoobarApplicationItem* self );
-gchar const* foobar_application_item_get_name       ( FoobarApplicationItem* self );
-gchar const* foobar_application_item_get_description( FoobarApplicationItem* self );
 gchar const* foobar_application_item_get_executable ( FoobarApplicationItem* self );
 gchar const* foobar_application_item_get_categories ( FoobarApplicationItem* self );
-GIcon*       foobar_application_item_get_icon       ( FoobarApplicationItem* self );
 gint64       foobar_application_item_get_frequency  ( FoobarApplicationItem* self );
 gboolean     foobar_application_item_match          ( FoobarApplicationItem* self,
                                                       gchar const* const*    terms );
-void         foobar_application_item_launch         ( FoobarApplicationItem* self );
 
 G_DECLARE_FINAL_TYPE( FoobarApplicationService, foobar_application_service, FOOBAR, APPLICATION_SERVICE, GObject )
 
diff --git a/src/services/meson.build b/src/services/meson.build
index 990102b..368c2f1 100644
--- a/src/services/meson.build
+++ b/src/services/meson.build
@@ -8,5 +8,8 @@ foobar_sources += files(
   'network-service.c',
   'bluetooth-service.c',
   'application-service.c',
+  'quick-answer-service.c',
   'configuration-service.c',
 )
+
+subdir('quick-answers')
diff --git a/src/services/quick-answer-service.c b/src/services/quick-answer-service.c
new file mode 100644
index 0000000..670a72f
--- /dev/null
+++ b/src/services/quick-answer-service.c
@@ -0,0 +1,360 @@
+#include "services/quick-answer-service.h"
+#include "services/quick-answers/math.h"
+#include "launcher-item.h"
+#include <gdk/gdk.h>
+
+//
+// FoobarQuickAnswer:
+//
+// A launcher item representing a quick, one-line answer to the query entered by the user.
+//
+
+struct _FoobarQuickAnswer
+{
+	GObject parent_instance;
+	gchar* title;
+	gchar* value;
+	GIcon* icon;
+};
+
+enum
+{
+	ANSWER_PROP_VALUE = 1,
+	ANSWER_PROP_TITLE,
+	ANSWER_PROP_DESCRIPTION,
+	ANSWER_PROP_ICON,
+	N_ANSWER_PROPS,
+};
+
+static GParamSpec* answer_props[N_ANSWER_PROPS] = { 0 };
+
+static void                   foobar_quick_answer_class_init                  ( FoobarQuickAnswerClass*      klass );
+static void                   foobar_quick_answer_launcher_item_interface_init( FoobarLauncherItemInterface* iface );
+static void                   foobar_quick_answer_init                        ( FoobarQuickAnswer*           self );
+static void                   foobar_quick_answer_get_property                ( GObject*                     object,
+                                                                                guint                        prop_id,
+                                                                                GValue*                      value,
+                                                                                GParamSpec*                  pspec );
+static void                   foobar_quick_answer_finalize                    ( GObject*                     object );
+static FoobarQuickAnswer*     foobar_quick_answer_new                         ( void );
+static gchar const*           foobar_quick_answer_get_title                   ( FoobarLauncherItem*          self );
+static gchar const*           foobar_quick_answer_get_description             ( FoobarLauncherItem*          self );
+static GIcon*                 foobar_quick_answer_get_icon                    ( FoobarLauncherItem*          self );
+static void                   foobar_quick_answer_activate                    ( FoobarLauncherItem*          self );
+static void                   foobar_quick_answer_set_title                   ( FoobarQuickAnswer*           self,
+                                                                                gchar const*                 value );
+static void                   foobar_quick_answer_set_value                   ( FoobarQuickAnswer*           self,
+                                                                                gchar const*                 value );
+static void                   foobar_quick_answer_set_icon                    ( FoobarQuickAnswer*           self,
+                                                                                GIcon*                       value );
+
+G_DEFINE_FINAL_TYPE_WITH_CODE(
+	FoobarQuickAnswer,
+	foobar_quick_answer,
+	G_TYPE_OBJECT,
+	G_IMPLEMENT_INTERFACE( FOOBAR_TYPE_LAUNCHER_ITEM, foobar_quick_answer_launcher_item_interface_init ) )
+
+//
+// FoobarQuickAnswerService:
+//
+// Service providing quick answers for search queries in the launcher (if available). This includes evaluating
+// mathematical expressions.
+//
+
+struct _FoobarQuickAnswerService
+{
+	GObject parent_instance;
+};
+
+static void               foobar_quick_answer_service_class_init( FoobarQuickAnswerServiceClass* klass );
+static void               foobar_quick_answer_service_init      ( FoobarQuickAnswerService*      self );
+static FoobarQuickAnswer* foobar_quick_answer_service_query_math( gchar const*                   query );
+
+G_DEFINE_FINAL_TYPE( FoobarQuickAnswerService, foobar_quick_answer_service, G_TYPE_OBJECT )
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Quick Answers
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Static initialization for quick answers.
+//
+void foobar_quick_answer_class_init( FoobarQuickAnswerClass* klass )
+{
+	GObjectClass* object_klass = G_OBJECT_CLASS( klass );
+	object_klass->get_property = foobar_quick_answer_get_property;
+	object_klass->finalize = foobar_quick_answer_finalize;
+
+	gpointer launcher_item_iface = g_type_default_interface_peek( FOOBAR_TYPE_LAUNCHER_ITEM );
+	answer_props[ANSWER_PROP_VALUE] = g_param_spec_string(
+		"value",
+		"Value",
+		"The raw value of the quick answer.",
+		NULL,
+		G_PARAM_READABLE );
+	answer_props[ANSWER_PROP_TITLE] = g_param_spec_override(
+		"title",
+		g_object_interface_find_property( launcher_item_iface, "title" ) );
+	answer_props[ANSWER_PROP_DESCRIPTION] = g_param_spec_override(
+		"description",
+		g_object_interface_find_property( launcher_item_iface, "description" ) );
+	answer_props[ANSWER_PROP_ICON] = g_param_spec_override(
+		"icon",
+		g_object_interface_find_property( launcher_item_iface, "icon" ) );
+	g_object_class_install_properties( object_klass, N_ANSWER_PROPS, answer_props );
+}
+
+//
+// Static initialization of the FoobarLauncherItem interface.
+//
+void foobar_quick_answer_launcher_item_interface_init( FoobarLauncherItemInterface* iface )
+{
+	iface->get_title = foobar_quick_answer_get_title;
+	iface->get_description = foobar_quick_answer_get_description;
+	iface->get_icon = foobar_quick_answer_get_icon;
+	iface->activate = foobar_quick_answer_activate;
+}
+
+//
+// Instance initialization for quick answers.
+//
+void foobar_quick_answer_init( FoobarQuickAnswer* self )
+{
+	(void)self;
+}
+
+//
+// Property getter implementation, mapping a property id to a method.
+//
+void foobar_quick_answer_get_property(
+	GObject*    object,
+	guint       prop_id,
+	GValue*     value,
+	GParamSpec* pspec )
+{
+	FoobarQuickAnswer* self = (FoobarQuickAnswer*)object;
+
+	switch ( prop_id )
+	{
+		case ANSWER_PROP_VALUE:
+			g_value_set_string( value, foobar_quick_answer_get_value( self ) );
+			break;
+		case ANSWER_PROP_TITLE:
+			g_value_set_string( value, foobar_launcher_item_get_title( FOOBAR_LAUNCHER_ITEM ( self ) ) );
+			break;
+		case ANSWER_PROP_DESCRIPTION:
+			g_value_set_string( value, foobar_launcher_item_get_description( FOOBAR_LAUNCHER_ITEM( self ) ) );
+			break;
+		case ANSWER_PROP_ICON:
+			g_value_set_object( value, foobar_launcher_item_get_icon( FOOBAR_LAUNCHER_ITEM( self ) ) );
+			break;
+		default:
+			G_OBJECT_WARN_INVALID_PROPERTY_ID( object, prop_id, pspec );
+			break;
+	}
+}
+
+//
+// Instance cleanup for quick answers.
+//
+void foobar_quick_answer_finalize( GObject* object )
+{
+	FoobarQuickAnswer* self = (FoobarQuickAnswer*)object;
+
+	g_clear_pointer( &self->title, g_free );
+	g_clear_pointer( &self->value, g_free );
+	g_clear_object( &self->icon );
+
+	G_OBJECT_CLASS( foobar_quick_answer_parent_class )->finalize( object );
+}
+
+//
+// Create a new, default-initialized quick answer.
+//
+FoobarQuickAnswer* foobar_quick_answer_new( void )
+{
+	return g_object_new( FOOBAR_TYPE_QUICK_ANSWER, NULL );
+}
+
+//
+// Get the raw value of the quick answer.
+//
+gchar const* foobar_quick_answer_get_value( FoobarQuickAnswer* self )
+{
+	g_return_val_if_fail( FOOBAR_IS_QUICK_ANSWER( self ), NULL );
+	return self->value;
+}
+
+//
+// Get the title for the quick answer.
+//
+gchar const* foobar_quick_answer_get_title( FoobarLauncherItem* item )
+{
+	FoobarQuickAnswer* self = ( FoobarQuickAnswer* )item;
+	return self->title;
+}
+
+//
+// Get the description shown below the title, always NULL for quick answers.
+//
+gchar const* foobar_quick_answer_get_description( FoobarLauncherItem* item )
+{
+	(void)item;
+	return NULL;
+}
+
+//
+// Get an icon representing the quick answer.
+//
+GIcon* foobar_quick_answer_get_icon( FoobarLauncherItem* item )
+{
+	FoobarQuickAnswer* self = ( FoobarQuickAnswer* )item;
+	return self->icon;
+}
+
+//
+// Copy the quick answer's value into the clipboard.
+//
+void foobar_quick_answer_activate( FoobarLauncherItem* item )
+{
+	FoobarQuickAnswer* self = ( FoobarQuickAnswer* )item;
+	if ( self->value )
+	{
+		GdkClipboard* clipboard = gdk_display_get_clipboard( gdk_display_get_default( ) );
+		gdk_clipboard_set_text( clipboard, self->value );
+	}
+}
+
+//
+// Update the raw value of the quick answer.
+//
+void foobar_quick_answer_set_value(
+	FoobarQuickAnswer* self,
+	gchar const*       value )
+{
+	g_return_if_fail( FOOBAR_IS_QUICK_ANSWER( self ) );
+
+	if ( g_strcmp0( self->value, value ) )
+	{
+		g_clear_pointer( &self->value, g_free );
+		self->value = g_strdup( value );
+		g_object_notify_by_pspec( G_OBJECT( self ), answer_props[ANSWER_PROP_VALUE] );
+	}
+}
+
+//
+// Update the title for the quick answer.
+//
+void foobar_quick_answer_set_title(
+	FoobarQuickAnswer* self,
+	gchar const*       value )
+{
+	g_return_if_fail( FOOBAR_IS_QUICK_ANSWER( self ) );
+
+	if ( g_strcmp0( self->title, value ) )
+	{
+		g_clear_pointer( &self->title, g_free );
+		self->title = g_strdup( value );
+		g_object_notify_by_pspec( G_OBJECT( self ), answer_props[ANSWER_PROP_TITLE] );
+	}
+}
+
+//
+// Update the icon representing the quick answer.
+//
+void foobar_quick_answer_set_icon(
+	FoobarQuickAnswer* self,
+	GIcon*             value )
+{
+	g_return_if_fail( FOOBAR_IS_QUICK_ANSWER( self ) );
+
+	if ( self->icon != value )
+	{
+		g_clear_object( &self->icon );
+		self->icon = value ? g_object_ref( value ) : NULL;
+		g_object_notify_by_pspec( G_OBJECT( self ), answer_props[ANSWER_PROP_ICON] );
+	}
+}
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Service Implementation
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Static initialization for the quick answer service.
+//
+void foobar_quick_answer_service_class_init( FoobarQuickAnswerServiceClass* klass )
+{
+	(void)klass;
+}
+
+//
+// Instance initialization for the quick answer service.
+//
+void foobar_quick_answer_service_init( FoobarQuickAnswerService* self )
+{
+	(void)self;
+}
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Public API
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Create a new quick answer service instance.
+//
+FoobarQuickAnswerService* foobar_quick_answer_service_new( void )
+{
+	return g_object_new( FOOBAR_TYPE_QUICK_ANSWER_SERVICE, NULL );
+}
+
+//
+// Query the service for a quick answer.
+//
+FoobarQuickAnswer* foobar_quick_answer_service_query(
+	FoobarQuickAnswerService* self,
+	gchar const*              query )
+{
+	(void)self;
+
+	FoobarQuickAnswer* result = foobar_quick_answer_service_query_math( query );
+	if ( result ) { return result; }
+
+	return NULL;
+}
+
+//
+// Try to parse the query as a mathematical expression and evaluate it.
+//
+FoobarQuickAnswer* foobar_quick_answer_service_query_math( gchar const* query )
+{
+	FoobarQuickAnswer* result = NULL;
+
+	gsize token_count;
+	g_autofree FoobarMathToken* tokens = foobar_math_lex( query, strlen( query ), &token_count );
+	if ( tokens )
+	{
+		FoobarMathExpression* expr = foobar_math_parse( tokens, token_count );
+		if ( expr )
+		{
+			// foobar_math_expression_print( expr, 0 );
+
+			FoobarMathValue val = { 0 };
+			if ( foobar_math_evaluate( expr, &val ) )
+			{
+				g_autofree gchar* value = foobar_math_value_to_string( val );
+				g_autofree gchar* title = g_strdup_printf( "= %s", value );
+				g_autoptr( GIcon ) icon = g_themed_icon_new( "fluent-calculator-symbolic" );
+				result = foobar_quick_answer_new( );
+				foobar_quick_answer_set_value( result, value );
+				foobar_quick_answer_set_title( result, title );
+				foobar_quick_answer_set_icon( result, icon );
+				foobar_math_value_free( val );
+			}
+
+			foobar_math_expression_free( expr );
+		}
+	}
+
+	return result;
+}
diff --git a/src/services/quick-answer-service.h b/src/services/quick-answer-service.h
new file mode 100644
index 0000000..adb0701
--- /dev/null
+++ b/src/services/quick-answer-service.h
@@ -0,0 +1,21 @@
+#pragma once
+
+#include <glib-object.h>
+#include <gio/gio.h>
+
+G_BEGIN_DECLS
+
+#define FOOBAR_TYPE_QUICK_ANSWER         foobar_quick_answer_get_type( )
+#define FOOBAR_TYPE_QUICK_ANSWER_SERVICE foobar_quick_answer_service_get_type( )
+
+G_DECLARE_FINAL_TYPE( FoobarQuickAnswer, foobar_quick_answer, FOOBAR, QUICK_ANSWER, GObject )
+
+gchar const* foobar_quick_answer_get_value( FoobarQuickAnswer* self );
+
+G_DECLARE_FINAL_TYPE( FoobarQuickAnswerService, foobar_quick_answer_service, FOOBAR, QUICK_ANSWER_SERVICE, GObject )
+
+FoobarQuickAnswerService* foobar_quick_answer_service_new      ( void );
+FoobarQuickAnswer*        foobar_quick_answer_service_query    ( FoobarQuickAnswerService* self,
+                                                                 gchar const*              query );
+
+G_END_DECLS
diff --git a/src/services/quick-answers/math-lexer.c b/src/services/quick-answers/math-lexer.c
new file mode 100644
index 0000000..7fbe877
--- /dev/null
+++ b/src/services/quick-answers/math-lexer.c
@@ -0,0 +1,248 @@
+#include "services/quick-answers/math.h"
+
+//
+// FoobarMathToken:
+//
+// A token in a mathematical expression. The token contents are left as-is and need not be null-terminated. For example,
+// "sin(pi) - 3" would be represented as:
+//  - IDENTIFIER: "sin"
+//  - PAREN_OPEN: "("
+//  - IDENTIFIER: "pi"
+//  - PAREN_CLOSE: ")"
+//  - MINUS: "-"
+//  - NUMBER: "3"
+//
+
+//
+// Lexer:
+//
+// The lexer context/state which is passed around.
+//
+
+typedef struct _Lexer Lexer;
+
+struct _Lexer
+{
+	GArray*      result;
+	gchar const* input;
+	gsize        input_length;
+	gsize        position;
+	gsize        token_start;
+};
+
+static gboolean char_is_whitespace( char c );
+static gboolean char_is_digit     ( char c );
+static gboolean char_is_identifier( char c );
+
+static char lexer_peek         ( Lexer const*        ctx,
+                                 gsize               offset );
+static char lexer_pop          ( Lexer*              ctx );
+static void lexer_begin_token  ( Lexer*              ctx );
+static void lexer_commit_token ( Lexer*              ctx,
+                                 FoobarMathTokenType type );
+static void lexer_commit_single( Lexer*              ctx,
+                                 FoobarMathTokenType type );
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Lexing
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Divide an input string into a list of tokens.
+//
+// On success, this will return a newly allocated array of tokens which should be freed using g_free. The number of
+// elements will be written into out_count.
+//
+// On error, this will return NULL.
+//
+FoobarMathToken* foobar_math_lex(
+	gchar const* input,
+	gsize        input_length,
+	gsize*       out_count )
+{
+	g_autoptr( GArray ) result = g_array_new( FALSE, TRUE, sizeof( FoobarMathToken ) );
+
+	Lexer ctx = { 0 };
+	ctx.result = result;
+	ctx.input = input;
+	ctx.input_length = input_length;
+
+	while ( ctx.position < input_length )
+	{
+		if ( char_is_whitespace( lexer_peek( &ctx, 0 ) ) )
+		{
+			// Skip whitespace.
+
+			lexer_pop( &ctx );
+		}
+		else if ( char_is_digit( lexer_peek( &ctx, 0 ) ) )
+		{
+			// Process numbers as a whole, don't allow whitespace inbetween.
+
+			lexer_begin_token( &ctx );
+			while ( char_is_digit( lexer_peek( &ctx, 0 ) ) )
+			{
+				lexer_pop( &ctx );
+			}
+
+			if ( lexer_peek( &ctx, 0 ) == '.' && char_is_digit( lexer_peek( &ctx, 1 ) ) )
+			{
+				lexer_pop( &ctx );
+				while ( char_is_digit( lexer_peek( &ctx, 0 ) ) )
+				{
+					lexer_pop( &ctx );
+				}
+			}
+
+			lexer_commit_token( &ctx, FOOBAR_MATH_TOKEN_NUMBER );
+		}
+		else if ( char_is_identifier( lexer_peek( &ctx, 0 ) ) )
+		{
+			// Don't validate identifiers, leave that to the parser.
+
+			lexer_begin_token( &ctx );
+			while ( char_is_identifier( lexer_peek( &ctx, 0 ) ) )
+			{
+				lexer_pop( &ctx );
+			}
+			lexer_commit_token( &ctx, FOOBAR_MATH_TOKEN_IDENTIFIER );
+		}
+		else if ( lexer_peek( &ctx, 0 ) == '(' )
+		{
+			lexer_commit_single( &ctx, FOOBAR_MATH_TOKEN_PAREN_OPEN );
+		}
+		else if ( lexer_peek( &ctx, 0 ) == ')' )
+		{
+			lexer_commit_single( &ctx, FOOBAR_MATH_TOKEN_PAREN_CLOSE );
+		}
+		else if ( lexer_peek( &ctx, 0 ) == '+' )
+		{
+			lexer_commit_single( &ctx, FOOBAR_MATH_TOKEN_PLUS );
+		}
+		else if ( lexer_peek( &ctx, 0 ) == '-' )
+		{
+			lexer_commit_single( &ctx, FOOBAR_MATH_TOKEN_MINUS );
+		}
+		else if ( lexer_peek( &ctx, 0 ) == '*' )
+		{
+			lexer_commit_single( &ctx, FOOBAR_MATH_TOKEN_MUL );
+		}
+		else if ( lexer_peek( &ctx, 0 ) == '/' )
+		{
+			lexer_commit_single( &ctx, FOOBAR_MATH_TOKEN_DIV );
+		}
+		else if ( lexer_peek( &ctx, 0 ) == '^' )
+		{
+			lexer_commit_single( &ctx, FOOBAR_MATH_TOKEN_POW );
+		}
+		else
+		{
+			// Unknown character.
+
+			return NULL;
+		}
+	}
+
+	return g_array_steal( result, out_count );
+}
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Character Classification
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Check if a character is a whitespace symbol (space, tab, carriage return).
+//
+gboolean char_is_whitespace( char c )
+{
+	return c == ' ' || c == '\t' || c == '\r';
+}
+
+//
+// Check if a character is a decimal digit.
+//
+gboolean char_is_digit( char c )
+{
+	return c >= '0' && c <= '9';
+}
+
+//
+// Check if a character belongs to an identifier (like "sin", "pi", etc.).
+//
+gboolean char_is_identifier( char c )
+{
+	// Identifiers are all lowercase ASCII.
+
+	return c >= 'a' && c <= 'z';
+}
+
+// ---------------------------------------------------------------------------------------------------------------------
+// State Helpers
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Peek at the current character without consuming it.
+//
+// If this is the end of the input string, return 0.
+//
+char lexer_peek(
+	Lexer const* ctx,
+	gsize        offset )
+{
+	gsize position = ctx->position + offset;
+	if ( position >= ctx->input_length ) { return 0; }
+
+	return ctx->input[position];
+}
+
+//
+// Consume the current character, moving forward to the next one.
+//
+// If this is the end of the input string, return 0.
+//
+char lexer_pop( Lexer* ctx )
+{
+	if ( ctx->position >= ctx->input_length ) { return 0; }
+
+	return ctx->input[ctx->position++];
+}
+
+//
+// Start recording a token by remembering the current position.
+//
+// The current character will be the first one in the token.
+//
+void lexer_begin_token( Lexer* ctx )
+{
+	ctx->token_start = ctx->position;
+}
+
+//
+// Stop recording a token, saving the string between the call to lexer_begin_token as the specified type.
+//
+// The current character will not be a part of the token.
+//
+void lexer_commit_token(
+	Lexer*              ctx,
+	FoobarMathTokenType type )
+{
+	FoobarMathToken token = { 0 };
+	token.data = &ctx->input[ctx->token_start];
+	token.length = ctx->position - ctx->token_start;
+	token.type = type;
+	g_array_append_val( ctx->result, token );
+}
+
+//
+// Consume the current character and record it as a token.
+//
+// This is equivalent to calling lexer_begin_token, lexer_pop, and lexer_commit_token.
+//
+void lexer_commit_single(
+	Lexer*              ctx,
+	FoobarMathTokenType type )
+{
+	lexer_begin_token( ctx );
+	lexer_pop( ctx );
+	lexer_commit_token( ctx, type );
+}
diff --git a/src/services/quick-answers/math-parser.c b/src/services/quick-answers/math-parser.c
new file mode 100644
index 0000000..17d976d
--- /dev/null
+++ b/src/services/quick-answers/math-parser.c
@@ -0,0 +1,414 @@
+#include "services/quick-answers/math.h"
+
+//
+// Parser:
+//
+// The parser context/state which is passed around.
+//
+
+typedef struct _Parser Parser;
+
+struct _Parser
+{
+	FoobarMathToken const* tokens;
+	gsize                  tokens_count;
+	gsize                  position;
+};
+
+//
+// InfixPrecedence:
+//
+// Value indicating how strongly infix operators should bind. The higher the value, the stronger they should bind.
+//
+
+typedef enum
+{
+	INFIX_PRECEDENCE_INVALID        = -1,
+	INFIX_PRECEDENCE_NONE           = 0,
+	INFIX_PRECEDENCE_ADDITIVE       = 1,
+	INFIX_PRECEDENCE_MULTIPLICATIVE = 2,
+	INFIX_PRECEDENCE_EXPONENTS      = 3,
+} InfixPrecedence;
+
+static FoobarMathExpression*  parser_process            ( Parser*                ctx,
+                                                          FoobarMathExpression*  lhs,
+                                                          InfixPrecedence        min_precedence );
+static FoobarMathExpression*  parser_process_single     ( Parser*                ctx,
+                                                          gboolean               allow_sign );
+static FoobarMathExpression*  parser_process_identifier ( Parser*                ctx );
+static FoobarMathExpression*  parser_process_number     ( Parser*                ctx );
+static FoobarMathExpression*  parser_process_function   ( Parser*                ctx,
+                                                          FoobarMathFunction     function );
+static FoobarMathExpression*  parser_process_parens     ( Parser*                ctx );
+static FoobarMathExpression*  parser_process_sign       ( Parser*                ctx );
+static FoobarMathToken const* parser_peek               ( Parser const*          ctx );
+static FoobarMathToken const* parser_pop                ( Parser*                ctx );
+static gboolean               parser_match_identifier   ( FoobarMathToken const* token,
+                                                          gchar const*           identifier );
+static InfixPrecedence        parser_operator_precedence( FoobarMathToken const* token );
+static FoobarMathOperation    parser_operator           ( FoobarMathToken const* token );
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Parsing
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Transform a sequence of tokens into a mathematical expression.
+//
+// On success, this will return a newly allocated expression which should be freed using foobar_math_expression_free.
+//
+// On error, this will return NULL.
+//
+FoobarMathExpression* foobar_math_parse(
+	FoobarMathToken const* tokens,
+	gsize                  tokens_count )
+{
+	Parser ctx = { 0 };
+	ctx.tokens = tokens;
+	ctx.tokens_count = tokens_count;
+
+	FoobarMathExpression* lhs = parser_process_single( &ctx, TRUE );
+	if ( !lhs ) { return NULL; }
+
+	FoobarMathExpression* expr = parser_process( &ctx, lhs, INFIX_PRECEDENCE_NONE );
+	if ( !expr ) { return NULL; }
+
+	if ( parser_peek( &ctx ) )
+	{
+		foobar_math_expression_free( expr );
+		return NULL;
+	}
+
+	return expr;
+}
+
+//
+// Process tokens until the end of the current precedence scope (indicated by min_precedence), starting at an operator.
+//
+FoobarMathExpression* parser_process(
+	Parser*               ctx,
+	FoobarMathExpression* lhs,
+	InfixPrecedence       min_precedence )
+{
+	FoobarMathToken const* op = parser_peek( ctx );
+	InfixPrecedence op_precedence = parser_operator_precedence( op );
+	while ( op_precedence >= min_precedence )
+	{
+		parser_pop( ctx );
+
+		FoobarMathExpression* rhs = parser_process_single( ctx, FALSE );
+		if ( !rhs )
+		{
+			foobar_math_expression_free( lhs );
+			return NULL;
+		}
+
+		FoobarMathToken const* next_op = parser_peek( ctx );
+		while ( parser_operator_precedence( next_op ) > op_precedence )
+		{
+			rhs = parser_process( ctx, rhs, op_precedence + 1 );
+			if ( !rhs )
+			{
+				foobar_math_expression_free( lhs );
+				return NULL;
+			}
+
+			next_op = parser_peek( ctx );
+		}
+
+		lhs = foobar_math_expression_new_operation( parser_operator( op ), lhs, rhs );
+
+		op = parser_peek( ctx );
+		op_precedence = parser_operator_precedence( op );
+	}
+
+	return lhs;
+}
+
+//
+// Process a single value which may be either a constant, function, number, expression enclosed in parenthesis or
+// negation.
+//
+// If an unexpected token is encountered (i.e. an operator), this will return FALSE.
+//
+FoobarMathExpression* parser_process_single(
+	Parser*  ctx,
+	gboolean allow_sign )
+{
+	FoobarMathToken const* token = parser_peek( ctx );
+	if ( !token ) { return NULL; }
+
+	switch ( token->type )
+	{
+		case FOOBAR_MATH_TOKEN_IDENTIFIER:
+			return parser_process_identifier( ctx );
+		case FOOBAR_MATH_TOKEN_NUMBER:
+			return parser_process_number( ctx );
+		case FOOBAR_MATH_TOKEN_PAREN_OPEN:
+			return parser_process_parens( ctx );
+		case FOOBAR_MATH_TOKEN_MINUS:
+		case FOOBAR_MATH_TOKEN_PLUS:
+			if ( !allow_sign ) { return NULL; }
+			return parser_process_sign( ctx );
+		case FOOBAR_MATH_TOKEN_PAREN_CLOSE:
+		case FOOBAR_MATH_TOKEN_MUL:
+		case FOOBAR_MATH_TOKEN_DIV:
+		case FOOBAR_MATH_TOKEN_POW:
+			return NULL;
+		default:
+			g_warn_if_reached( );
+			return NULL;
+	}
+}
+
+//
+// Parse an identifier.
+//
+// If the identifier is a function, this will expected parenthesis and an expression afterwards.
+//
+FoobarMathExpression* parser_process_identifier( Parser* ctx )
+{
+	FoobarMathToken const* token = parser_pop( ctx );
+	if ( parser_match_identifier( token, "pi" ) )
+	{
+		return foobar_math_expression_new_constant( FOOBAR_MATH_CONSTANT_PI );
+	}
+	else if ( parser_match_identifier( token, "e" ) )
+	{
+		return foobar_math_expression_new_constant( FOOBAR_MATH_CONSTANT_E );
+	}
+	else if ( parser_match_identifier( token, "exp" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_EXP );
+	}
+	else if ( parser_match_identifier( token, "sqrt" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_SQRT );
+	}
+	else if ( parser_match_identifier( token, "sin" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_SIN );
+	}
+	else if ( parser_match_identifier( token, "cos" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_COS );
+	}
+	else if ( parser_match_identifier( token, "sec" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_SEC );
+	}
+	else if ( parser_match_identifier( token, "csc" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_CSC );
+	}
+	else if ( parser_match_identifier( token, "tan" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_TAN );
+	}
+	else if ( parser_match_identifier( token, "cot" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_COT );
+	}
+	else if ( parser_match_identifier( token, "arcsin" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_ARCSIN );
+	}
+	else if ( parser_match_identifier( token, "arccos" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_ARCCOS );
+	}
+	else if ( parser_match_identifier( token, "arcsec" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_ARCSEC );
+	}
+	else if ( parser_match_identifier( token, "arccsc" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_ARCCSC );
+	}
+	else if ( parser_match_identifier( token, "arctan" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_ARCTAN );
+	}
+	else if ( parser_match_identifier( token, "arccot" ) )
+	{
+		return parser_process_function( ctx, FOOBAR_MATH_FUNCTION_ARCCOT );
+	}
+	else
+	{
+		return NULL;
+	}
+}
+
+//
+// Process a numeric value.
+//
+FoobarMathExpression* parser_process_number( Parser* ctx )
+{
+	FoobarMathToken const* token = parser_pop( ctx );
+	FoobarMathValue value = { 0 };
+	if ( !foobar_math_value_from_string( token->data, token->length, &value ) )
+	{
+		return NULL;
+	}
+
+	return foobar_math_expression_new_value( value );
+}
+
+//
+// Process a function's parameter which should be enclosed in parenthesis.
+//
+FoobarMathExpression* parser_process_function(
+	Parser*            ctx,
+	FoobarMathFunction function )
+{
+	FoobarMathToken const* opening_paren = parser_peek( ctx );
+	if ( !opening_paren || opening_paren->type != FOOBAR_MATH_TOKEN_PAREN_OPEN )
+	{
+		return NULL;
+	}
+
+	FoobarMathExpression* arg = parser_process_parens( ctx );
+	if ( !arg ) { return NULL; }
+
+	return foobar_math_expression_new_function( function, arg );
+}
+
+//
+// Process an expression enclosed in parenthesis.
+//
+FoobarMathExpression* parser_process_parens( Parser* ctx )
+{
+	parser_pop( ctx );
+	FoobarMathExpression* lhs = parser_process_single( ctx, TRUE );
+	if ( !lhs ) { return NULL; }
+	FoobarMathExpression* result = parser_process( ctx, lhs, INFIX_PRECEDENCE_NONE );
+	if ( !result ) { return NULL; }
+	FoobarMathToken const* closing_paren = parser_pop( ctx );
+	if ( !closing_paren || closing_paren->type != FOOBAR_MATH_TOKEN_PAREN_CLOSE )
+	{
+		foobar_math_expression_free( result );
+		return NULL;
+	}
+	return result;
+}
+
+//
+// Process a sign (- or +) which may be used for negation of an expression.
+//
+FoobarMathExpression* parser_process_sign( Parser* ctx )
+{
+	FoobarMathToken const* token = parser_pop( ctx );
+	FoobarMathExpression* result = parser_process_single( ctx, FALSE );
+	if ( !result ) { return NULL; }
+
+	if ( token->type == FOOBAR_MATH_TOKEN_MINUS )
+	{
+		return foobar_math_expression_new_function( FOOBAR_MATH_FUNCTION_NEGATE, result );
+	}
+	else
+	{
+		return result;
+	}
+}
+
+// ---------------------------------------------------------------------------------------------------------------------
+// State Helpers
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Peek at the current token without consuming it.
+//
+// If this is the end of the token list, return NULL.
+//
+FoobarMathToken const* parser_peek( Parser const* ctx )
+{
+	if ( ctx->position >= ctx->tokens_count ) { return NULL; }
+
+	return &ctx->tokens[ctx->position];
+}
+
+//
+// Consume the current token.
+//
+// If this is the end of the token list, return NULL.
+//
+FoobarMathToken const* parser_pop( Parser* ctx )
+{
+	if ( ctx->position >= ctx->tokens_count ) { return NULL; }
+
+	return &ctx->tokens[ctx->position++];
+}
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Match a token's string against the given identifier string.
+//
+// This is necessary because the token's content is not a null-terminated string.
+//
+gboolean parser_match_identifier(
+	FoobarMathToken const* token,
+	gchar const*           identifier )
+{
+	if ( strlen( identifier ) != token->length ) { return FALSE; }
+
+	return !strncmp( token->data, identifier, token->length );
+}
+
+//
+// Get the precedence of an infix operator token or INVALID.
+//
+InfixPrecedence parser_operator_precedence( FoobarMathToken const* token )
+{
+	if ( token )
+	{
+		switch ( token->type )
+		{
+			case FOOBAR_MATH_TOKEN_PLUS:
+			case FOOBAR_MATH_TOKEN_MINUS:
+				return INFIX_PRECEDENCE_ADDITIVE;
+			case FOOBAR_MATH_TOKEN_MUL:
+			case FOOBAR_MATH_TOKEN_DIV:
+				return INFIX_PRECEDENCE_MULTIPLICATIVE;
+			case FOOBAR_MATH_TOKEN_POW:
+				return INFIX_PRECEDENCE_EXPONENTS;
+			case FOOBAR_MATH_TOKEN_IDENTIFIER:
+			case FOOBAR_MATH_TOKEN_NUMBER:
+			case FOOBAR_MATH_TOKEN_PAREN_OPEN:
+			case FOOBAR_MATH_TOKEN_PAREN_CLOSE:
+			default:
+				break;
+		}
+	}
+
+	return INFIX_PRECEDENCE_INVALID;
+}
+
+//
+// Get the operation for an infix operator token. This requires the token to be valid.
+//
+FoobarMathOperation parser_operator( FoobarMathToken const* token )
+{
+	switch ( token->type )
+	{
+		case FOOBAR_MATH_TOKEN_PLUS:
+			return FOOBAR_MATH_OPERATION_ADD;
+		case FOOBAR_MATH_TOKEN_MINUS:
+			return FOOBAR_MATH_OPERATION_SUB;
+		case FOOBAR_MATH_TOKEN_MUL:
+			return FOOBAR_MATH_OPERATION_MUL;
+		case FOOBAR_MATH_TOKEN_DIV:
+			return FOOBAR_MATH_OPERATION_DIV;
+		case FOOBAR_MATH_TOKEN_POW:
+			return FOOBAR_MATH_OPERATION_POW;
+		case FOOBAR_MATH_TOKEN_IDENTIFIER:
+		case FOOBAR_MATH_TOKEN_NUMBER:
+		case FOOBAR_MATH_TOKEN_PAREN_OPEN:
+		case FOOBAR_MATH_TOKEN_PAREN_CLOSE:
+		default:
+			g_warn_if_reached( );
+			return 0;
+	}
+}
diff --git a/src/services/quick-answers/math.c b/src/services/quick-answers/math.c
new file mode 100644
index 0000000..69219e2
--- /dev/null
+++ b/src/services/quick-answers/math.c
@@ -0,0 +1,851 @@
+#define _GNU_SOURCE
+
+#include "services/quick-answers/math.h"
+#include <math.h>
+
+//
+// FoobarMathExpression:
+//
+// A fully parsed mathematical expression which can be evaluated, for example "sin(pi) - 3" would be represented as:
+//  - Operation: SUB
+//    - Function: SIN
+//      - Constant: PI
+//    - Value: 3
+//
+
+struct _FoobarMathExpression
+{
+	FoobarMathExpressionType type;
+
+	union
+	{
+		struct
+		{
+			FoobarMathValue v;
+		} value;
+
+		struct
+		{
+			FoobarMathFunction f;
+			FoobarMathExpression* input;
+		} function;
+
+		struct
+		{
+			FoobarMathConstant c;
+		} constant;
+
+		struct
+		{
+			FoobarMathOperation o;
+			FoobarMathExpression* lhs;
+			FoobarMathExpression* rhs;
+		} operation;
+	};
+};
+
+//
+// FoobarMathValue:
+//
+// Representation of a value. The goal of this memory structure is to store the value as an integer for as long as
+// possible. Because of this, there is a "decimal_places" field, so the actual value of an integer is
+// $v * 10^(-decimal_places)$.
+//
+// If absolutely necessary (for example, because we use a function like sin), the value is converted to a floating-point
+// value.
+//
+// Note that we use GMP to store the integer value to allow for arbitrarily large values. Because of this, the structure
+// should always be freed using foobar_math_value_free.
+//
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Expressions
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Helper to allocate a new FoobarMathExpression representing a value.
+//
+// Ownership of "value" is transferred to the new expression.
+//
+FoobarMathExpression* foobar_math_expression_new_value( FoobarMathValue value )
+{
+	FoobarMathExpression* res = g_new0( FoobarMathExpression, 1 );
+	res->type = FOOBAR_MATH_EXPRESSION_VALUE;
+	res->value.v = value;
+	return res;
+}
+
+//
+// Helper to allocate a new FoobarMathExpression representing a function to be evaluated with another expression as its
+// parameter.
+//
+// Ownership of "input" is transferred to the new expression.
+//
+FoobarMathExpression* foobar_math_expression_new_function(
+	FoobarMathFunction    function,
+    FoobarMathExpression* input )
+{
+	FoobarMathExpression* res = g_new0( FoobarMathExpression, 1 );
+	res->type = FOOBAR_MATH_EXPRESSION_FUNCTION;
+	res->function.f = function;
+	res->function.input = input;
+	return res;
+}
+
+//
+// Helper to allocate a new FoobarMathExpression representing a known constant.
+//
+FoobarMathExpression* foobar_math_expression_new_constant( FoobarMathConstant constant )
+{
+	FoobarMathExpression* res = g_new0( FoobarMathExpression, 1 );
+	res->type = FOOBAR_MATH_EXPRESSION_CONSTANT;
+	res->constant.c = constant;
+	return res;
+}
+
+//
+// Helper to allocate a new FoobarMathExpression representing an operation to be evaluated with two expressions as its
+// parameters.
+//
+// Ownership of "lhs" and "rhs" is transferred to the new expression.
+//
+FoobarMathExpression* foobar_math_expression_new_operation(
+	FoobarMathOperation   operation,
+	FoobarMathExpression* lhs,
+	FoobarMathExpression* rhs )
+{
+	FoobarMathExpression* res = g_new0( FoobarMathExpression, 1 );
+	res->type = FOOBAR_MATH_EXPRESSION_OPERATION;
+	res->operation.o = operation;
+	res->operation.lhs = lhs;
+	res->operation.rhs = rhs;
+	return res;
+}
+
+//
+// Release the memory associated with a mathematical expression, along with the expressions it owns.
+//
+void foobar_math_expression_free( FoobarMathExpression* expression )
+{
+	if ( expression )
+	{
+		switch ( expression->type )
+		{
+			case FOOBAR_MATH_EXPRESSION_VALUE:
+				foobar_math_value_free( expression->value.v );
+				break;
+			case FOOBAR_MATH_EXPRESSION_FUNCTION:
+				foobar_math_expression_free( expression->function.input );
+				break;
+			case FOOBAR_MATH_EXPRESSION_CONSTANT:
+				break;
+			case FOOBAR_MATH_EXPRESSION_OPERATION:
+				foobar_math_expression_free( expression->operation.lhs );
+				foobar_math_expression_free( expression->operation.rhs );
+				break;
+			default:
+				g_warn_if_reached( );
+				break;
+		}
+
+		g_free( expression );
+	}
+}
+
+//
+// Print a tree representation of a mathematical expression.
+//
+// This is mainly useful for debugging. "indentation" describes the current indentation level for the recursive call
+// (should be 0 initially).
+//
+void foobar_math_expression_print(
+	FoobarMathExpression const* expr,
+	gint                        indentation )
+{
+	for (gint i = 0; i < indentation; ++i) { g_print("| "); }
+	switch ( expr->type )
+	{
+        case FOOBAR_MATH_EXPRESSION_VALUE:
+		{
+			g_autofree gchar* val = foobar_math_value_to_string( expr->value.v );
+			g_print( "%s\n", val );
+			break;
+		}
+        case FOOBAR_MATH_EXPRESSION_FUNCTION:
+			switch ( expr->function.f )
+			{
+				case FOOBAR_MATH_FUNCTION_NEGATE:
+					g_print( "-\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_SIN:
+					g_print( "sin\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_COS:
+					g_print( "cos\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_SEC:
+					g_print( "sec\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_CSC:
+					g_print( "csc\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_TAN:
+					g_print( "tan\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_COT:
+					g_print( "cot\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCSIN:
+					g_print( "arcsin\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCCOS:
+					g_print( "arccos\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCSEC:
+					g_print( "arcsec\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCCSC:
+					g_print( "arccsc\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCTAN:
+					g_print( "arctan\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCCOT:
+					g_print( "arccot\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_EXP:
+					g_print( "exp\n" );
+					break;
+				case FOOBAR_MATH_FUNCTION_SQRT:
+					g_print( "sqrt\n" );
+					break;
+				default:
+					g_warn_if_reached( );
+					break;
+			}
+			foobar_math_expression_print( expr->function.input, indentation + 1 );
+			break;
+        case FOOBAR_MATH_EXPRESSION_CONSTANT:
+			switch ( expr->constant.c )
+			{
+				case FOOBAR_MATH_CONSTANT_PI:
+					g_print( "pi\n" );
+					break;
+				case FOOBAR_MATH_CONSTANT_E:
+					g_print( "e\n" );
+					break;
+				default:
+					g_warn_if_reached( );
+					break;
+			}
+			break;
+        case FOOBAR_MATH_EXPRESSION_OPERATION:
+			switch ( expr->operation.o )
+			{
+				case FOOBAR_MATH_OPERATION_ADD:
+					g_print( "+\n" );
+					break;
+				case FOOBAR_MATH_OPERATION_SUB:
+					g_print( "-\n" );
+					break;
+				case FOOBAR_MATH_OPERATION_MUL:
+					g_print( "*\n" );
+					break;
+				case FOOBAR_MATH_OPERATION_DIV:
+					g_print( "/\n" );
+					break;
+				case FOOBAR_MATH_OPERATION_POW:
+					g_print( "^\n" );
+					break;
+				default:
+					g_warn_if_reached( );
+					break;
+			}
+			foobar_math_expression_print( expr->operation.lhs, indentation + 1 );
+			foobar_math_expression_print( expr->operation.rhs, indentation + 1 );
+			break;
+		default:
+			g_warn_if_reached( );
+			break;
+	}
+}
+
+//
+// Evaluate an expression, producing a value.
+//
+// On success (indicated by the return value TRUE), the value should be freed using foobar_math_value_free.
+//
+gboolean foobar_math_evaluate(
+	FoobarMathExpression const* expr,
+	FoobarMathValue*            out_value )
+{
+	switch ( expr->type )
+	{
+        case FOOBAR_MATH_EXPRESSION_VALUE:
+			foobar_math_value_copy( expr->value.v, out_value );
+			return TRUE;
+        case FOOBAR_MATH_EXPRESSION_CONSTANT:
+			switch ( expr->constant.c )
+			{
+				case FOOBAR_MATH_CONSTANT_PI:
+					foobar_math_value_from_float( M_PIl, out_value );
+					return TRUE;
+				case FOOBAR_MATH_CONSTANT_E:
+					foobar_math_value_from_float( M_El, out_value );
+					return TRUE;
+				default:
+					g_warn_if_reached( );
+					return FALSE;
+			}
+        case FOOBAR_MATH_EXPRESSION_FUNCTION:
+		{
+			FoobarMathValue input = { 0 };
+			if ( !foobar_math_evaluate( expr->function.input, &input ) ) { return FALSE; }
+
+			if ( expr->function.f == FOOBAR_MATH_FUNCTION_NEGATE )
+			{
+				*out_value = input;
+				foobar_math_value_negate( out_value );
+				return TRUE;
+			}
+
+			long double input_float = foobar_math_value_to_float( input );
+			foobar_math_value_free( input );
+
+			long double result = NAN;
+			switch ( expr->function.f )
+			{
+				case FOOBAR_MATH_FUNCTION_SIN:
+					result = sinl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_COS:
+					result = cosl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_SEC:
+					result = 1.L / cosl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_CSC:
+					result = 1.L / sinl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_TAN:
+					result = tanl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_COT:
+					result = 1.L / tanl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCSIN:
+					result = asinl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCCOS:
+					result = acosl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCSEC:
+					result = acosl( 1.L / input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCCSC:
+					result = asinl( 1.L / input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCTAN:
+					result = atanl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_ARCCOT:
+					result = atanl( 1.L / input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_EXP:
+					result = expl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_SQRT:
+					result = sqrtl( input_float );
+					break;
+				case FOOBAR_MATH_FUNCTION_NEGATE:
+				default:
+					g_warn_if_reached( );
+					return FALSE;
+			}
+
+			if ( isnanl( result ) || isinfl( result ) ) { return FALSE; }
+
+			foobar_math_value_from_float( result, out_value );
+			return TRUE;
+		}
+        case FOOBAR_MATH_EXPRESSION_OPERATION:
+		{
+			FoobarMathValue lhs = { 0 };
+			if ( !foobar_math_evaluate( expr->operation.lhs, &lhs ) ) { return FALSE; }
+			FoobarMathValue rhs = { 0 };
+			if ( !foobar_math_evaluate( expr->operation.rhs, &rhs ) )
+			{
+				foobar_math_value_free( lhs );
+				return FALSE;
+			}
+
+			gboolean success = FALSE;
+			switch ( expr->operation.o )
+			{
+				case FOOBAR_MATH_OPERATION_ADD:
+					success = foobar_math_value_add( &lhs, &rhs, out_value );
+					break;
+				case FOOBAR_MATH_OPERATION_SUB:
+					success = foobar_math_value_sub( &lhs, &rhs, out_value );
+					break;
+				case FOOBAR_MATH_OPERATION_MUL:
+					success = foobar_math_value_mul( &lhs, &rhs, out_value );
+					break;
+				case FOOBAR_MATH_OPERATION_DIV:
+					success = foobar_math_value_div( &lhs, &rhs, out_value );
+					break;
+				case FOOBAR_MATH_OPERATION_POW:
+					success = foobar_math_value_pow( &lhs, &rhs, out_value );
+					break;
+				default:
+					g_warn_if_reached( );
+					break;
+			}
+
+			foobar_math_value_free( lhs );
+			foobar_math_value_free( rhs );
+
+			return success;
+		}
+		default:
+			g_warn_if_reached( );
+			return FALSE;
+	}
+}
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Values
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Initialize a new integer value to zero.
+//
+// After this, the structure should be freed using foobar_math_value_free.
+//
+void foobar_math_value_new_int( FoobarMathValue* out_value )
+{
+	out_value->type = FOOBAR_MATH_VALUE_INT;
+	mpz_init( out_value->int_value.v );
+	out_value->int_value.decimal_places = 0;
+}
+
+//
+// Initialize a new value from its floating point representation.
+//
+// Although technically not necessary, you should still call foobar_math_value_free on the returned value.
+//
+void foobar_math_value_from_float(
+	long double      value,
+	FoobarMathValue* out_value )
+{
+	out_value->type = FOOBAR_MATH_VALUE_FLOAT;
+	out_value->float_value.v = value;
+}
+
+//
+// Parse a value from its string representation. This will always return an integer representation.
+//
+// On success (return value TRUE), the structure should be freed using foobar_math_value_free.
+//
+gboolean foobar_math_value_from_string(
+	gchar const*     input,
+	gsize            input_length,
+	FoobarMathValue* out_value )
+{
+	g_autofree gchar* without_sep = g_new0( gchar, input_length + 1 );
+	gsize sep_pos = input_length - 1;
+	gsize j = 0;
+	for ( gsize i = 0; i < input_length; ++i )
+	{
+		if ( input[i] == '.' )
+		{
+			sep_pos = i;
+		}
+		else
+		{
+			without_sep[j++] = input[i];
+		}
+	}
+
+	foobar_math_value_new_int( out_value );
+	out_value->int_value.decimal_places = input_length - 1 - sep_pos;
+	if ( mpz_init_set_str( out_value->int_value.v, without_sep, 10 ) == -1 )
+	{
+		mpz_clear( out_value->int_value.v );
+		return FALSE;
+	}
+
+	return TRUE;
+}
+
+//
+// Create a copy of a value, allocating necessary memory.
+//
+// After this, the structure should be freed using foobar_math_value_free.
+//
+void foobar_math_value_copy(
+	FoobarMathValue  value,
+	FoobarMathValue* out_value )
+{
+	*out_value = value;
+
+	switch ( value.type )
+	{
+		case FOOBAR_MATH_VALUE_INT:
+			mpz_init_set( out_value->int_value.v, value.int_value.v );
+			break;
+		case FOOBAR_MATH_VALUE_FLOAT:
+			break;
+		default:
+			g_warn_if_reached( );
+			break;
+	}
+}
+
+//
+// Release memory associated with a value.
+//
+// This is necessary because the integer representation is stored using GMP, which can store arbitrarily large values.
+//
+void foobar_math_value_free( FoobarMathValue value )
+{
+	switch ( value.type )
+	{
+		case FOOBAR_MATH_VALUE_INT:
+			mpz_clear( value.int_value.v );
+			break;
+		case FOOBAR_MATH_VALUE_FLOAT:
+			break;
+		default:
+			g_warn_if_reached( );
+			break;
+	}
+}
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Operations
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Operation equivalent to "value *= -1".
+//
+void foobar_math_value_negate( FoobarMathValue* value )
+{
+	switch ( value->type )
+	{
+		case FOOBAR_MATH_VALUE_INT:
+			mpz_neg( value->int_value.v, value->int_value.v );
+			break;
+		case FOOBAR_MATH_VALUE_FLOAT:
+			value->float_value.v = -value->float_value.v;
+			break;
+		default:
+			g_warn_if_reached( );
+			break;
+	}
+}
+
+//
+// Operation setting "out_value = lhs + rhs".
+//
+// After this, the result value should be freed using foobar_math_value_free.
+//
+gboolean foobar_math_value_add(
+	FoobarMathValue* lhs,
+	FoobarMathValue* rhs,
+	FoobarMathValue* out_value )
+{
+	if ( foobar_math_value_unify_integers( lhs, rhs ) )
+	{
+		foobar_math_value_new_int( out_value );
+		out_value->int_value.decimal_places = lhs->int_value.decimal_places;
+		mpz_add( out_value->int_value.v, lhs->int_value.v, rhs->int_value.v );
+		return TRUE;
+	}
+
+	long double lhs_float = foobar_math_value_to_float( *lhs );
+	long double rhs_float = foobar_math_value_to_float( *rhs );
+	foobar_math_value_from_float( lhs_float + rhs_float, out_value );
+	return TRUE;
+}
+
+//
+// Operation setting "out_value = lhs - rhs".
+//
+// After this, the result value should be freed using foobar_math_value_free.
+//
+gboolean foobar_math_value_sub(
+	FoobarMathValue* lhs,
+	FoobarMathValue* rhs,
+	FoobarMathValue* out_value )
+{
+	if ( foobar_math_value_unify_integers( lhs, rhs ) )
+	{
+		foobar_math_value_new_int( out_value );
+		out_value->int_value.decimal_places = lhs->int_value.decimal_places;
+		mpz_sub( out_value->int_value.v, lhs->int_value.v, rhs->int_value.v );
+		return TRUE;
+	}
+
+	long double lhs_float = foobar_math_value_to_float( *lhs );
+	long double rhs_float = foobar_math_value_to_float( *rhs );
+	foobar_math_value_from_float( lhs_float - rhs_float, out_value );
+	return TRUE;
+}
+
+//
+// Operation setting "out_value = lhs * rhs".
+//
+// After this, the result value should be freed using foobar_math_value_free.
+//
+gboolean foobar_math_value_mul(
+	FoobarMathValue* lhs,
+	FoobarMathValue* rhs,
+	FoobarMathValue* out_value )
+{
+	if ( lhs->type == FOOBAR_MATH_VALUE_INT && rhs->type == FOOBAR_MATH_VALUE_INT )
+	{
+		foobar_math_value_new_int( out_value );
+		out_value->int_value.decimal_places = lhs->int_value.decimal_places + rhs->int_value.decimal_places;
+		mpz_mul( out_value->int_value.v, lhs->int_value.v, rhs->int_value.v );
+		return TRUE;
+	}
+
+	long double lhs_float = foobar_math_value_to_float( *lhs );
+	long double rhs_float = foobar_math_value_to_float( *rhs );
+	foobar_math_value_from_float( lhs_float * rhs_float, out_value );
+	return TRUE;
+}
+
+//
+// Operation setting "out_value = lhs / rhs".
+//
+// After this, the result value should be freed using foobar_math_value_free.
+//
+gboolean foobar_math_value_div(
+	FoobarMathValue* lhs,
+	FoobarMathValue* rhs,
+	FoobarMathValue* out_value )
+{
+	if ( lhs->type == FOOBAR_MATH_VALUE_INT && rhs->type == FOOBAR_MATH_VALUE_INT )
+	{
+		if ( mpz_sgn( rhs->int_value.v ) == 0 ) { return FALSE; }
+
+		if ( rhs->int_value.decimal_places > lhs->int_value.decimal_places )
+		{
+			foobar_math_value_unify_integers( lhs, rhs );
+		}
+
+		foobar_math_value_new_int( out_value );
+		out_value->int_value.decimal_places = lhs->int_value.decimal_places - rhs->int_value.decimal_places;
+		mpz_t rem;
+		mpz_init( rem );
+		mpz_divmod( out_value->int_value.v, rem, lhs->int_value.v, rhs->int_value.v );
+		gboolean result_is_int = mpz_sgn( rem ) == 0;
+		mpz_clear( rem );
+
+		if ( result_is_int ) { return TRUE; }
+		foobar_math_value_free( *out_value );
+	}
+
+	long double lhs_float = foobar_math_value_to_float( *lhs );
+	long double rhs_float = foobar_math_value_to_float( *rhs );
+	long double result = lhs_float / rhs_float;
+	if ( isnanl( result ) || isinfl( result ) ) { return FALSE; }
+	foobar_math_value_from_float( result, out_value );
+	return TRUE;
+}
+
+//
+// Operation setting "out_value = lhs ^ rhs".
+//
+// After this, the result value should be freed using foobar_math_value_free.
+//
+gboolean foobar_math_value_pow(
+	FoobarMathValue* lhs,
+	FoobarMathValue* rhs,
+	FoobarMathValue* out_value )
+{
+	if ( lhs->type == FOOBAR_MATH_VALUE_INT &&
+			rhs->type == FOOBAR_MATH_VALUE_INT &&
+			rhs->int_value.decimal_places == 0 &&
+			mpz_fits_ulong_p( rhs->int_value.v ) )
+	{
+		unsigned long exp = mpz_get_ui( rhs->int_value.v );
+		foobar_math_value_new_int( out_value );
+		out_value->int_value.decimal_places = lhs->int_value.decimal_places * exp;
+		mpz_pow_ui( out_value->int_value.v, lhs->int_value.v, exp );
+		return TRUE;
+	}
+
+	long double lhs_float = foobar_math_value_to_float( *lhs );
+	long double rhs_float = foobar_math_value_to_float( *rhs );
+	long double result = powl( lhs_float, rhs_float );
+	if ( isnanl( result ) || isinfl( result ) ) { return FALSE; }
+	foobar_math_value_from_float( result, out_value );
+	return TRUE;
+}
+
+//
+// Ensure that two integer values have the same number of decimal places.
+//
+// This may change the in-memory-representation of a value, but not its actual value. It only increases the precision of
+// one value
+//
+// If either a or b is not stored as an integer, this will return FALSE.
+//
+gboolean foobar_math_value_unify_integers(
+	FoobarMathValue* a,
+	FoobarMathValue* b )
+{
+	if ( a->type != FOOBAR_MATH_VALUE_INT || b->type != FOOBAR_MATH_VALUE_INT ) { return FALSE; }
+
+	// Extend the less precise representation so both numbers have the same number of decimal places.
+
+	gsize decimal_places = MAX( a->int_value.decimal_places, b->int_value.decimal_places );
+
+	mpz_t exp;
+	mpz_init( exp );
+
+	if ( decimal_places > a->int_value.decimal_places )
+	{
+		mpz_ui_pow_ui( exp, 10, decimal_places - a->int_value.decimal_places );
+		mpz_mul( a->int_value.v, a->int_value.v, exp );
+	}
+
+	if ( decimal_places > b->int_value.decimal_places )
+	{
+		mpz_ui_pow_ui( exp, 10, decimal_places - b->int_value.decimal_places );
+		mpz_mul( b->int_value.v, b->int_value.v, exp );
+	}
+
+	mpz_clear( exp );
+
+	a->int_value.decimal_places = b->int_value.decimal_places = decimal_places;
+
+	return TRUE;
+}
+
+// ---------------------------------------------------------------------------------------------------------------------
+// Conversions
+// ---------------------------------------------------------------------------------------------------------------------
+
+//
+// Format a value as a string.
+//
+// The result is a null-terminated string which should be freed using g_free.
+//
+gchar* foobar_math_value_to_string( FoobarMathValue value )
+{
+	switch ( value.type )
+	{
+		case FOOBAR_MATH_VALUE_INT:
+		{
+			gsize cap = mpz_sizeinbase( value.int_value.v, 10 );
+			cap = MAX( cap, value.int_value.decimal_places + 1 ); // pad with zeroes if necessary
+			gchar* result = g_new0( gchar, cap + 3 ); // length + null terminator + sign + separator
+			mpz_get_str( result, 10, value.int_value.v );
+			gsize len = strlen( result ); // actual size may be 1 char less (+ len now also includes sign)
+			gboolean has_sign = result[0] == '-';
+			if ( has_sign )
+			{
+				// add the sign back later, makes everything else easier
+				result += 1;
+				len -= 1;
+			}
+			// pad with leading zeroes if necessary
+			gsize padded_len = MAX( len, value.int_value.decimal_places + 1 );
+			memmove( &result[padded_len - len], result, len + 1 );
+			memset( result, '0', padded_len - len );
+			len = padded_len;
+			gboolean trailing_zeros = TRUE;
+			gsize decimal_places = value.int_value.decimal_places;
+			gsize actual_decimal_places = decimal_places;
+			for ( gsize i = 0; i < decimal_places; ++i )
+			{
+				if ( trailing_zeros && result[len - 1 - i] == '0' )
+				{
+					result[len - 1 - i] = '\0';
+					actual_decimal_places -= 1;
+				}
+				else
+				{
+					trailing_zeros = FALSE;
+				}
+			}
+			if ( actual_decimal_places > 0 )
+			{
+				memmove( &result[len + 1 - decimal_places], &result[len - decimal_places], decimal_places + 1 );
+				result[len - decimal_places] = '.';
+			}
+			if ( has_sign )
+			{
+				result -= 1;
+				len += 1;
+			}
+			return result;
+		}
+		case FOOBAR_MATH_VALUE_FLOAT:
+		{
+			gchar* result = g_strdup_printf( "%.30Lf", value.float_value.v );
+
+			// trim trailing zeros
+			size_t len = strlen( result );
+			for ( gsize i = 0; i < len; ++i )
+			{
+				if ( result[len - 1 - i] == '.' )
+				{
+					result[len - 1 - i] = '\0';
+					break;
+				}
+				else if ( result[len - 1 - i] == '0' )
+				{
+					result[len - 1 - i] = '\0';
+				}
+				else
+				{
+					break;
+				}
+			}
+
+			return result;
+		}
+		default:
+			g_warn_if_reached( );
+			return NULL;
+	}
+}
+
+//
+// Convert a value to its floating-point representation.
+//
+// This may be a lossy conversion and should only be done if absolutely necessary.
+//
+long double foobar_math_value_to_float( FoobarMathValue value )
+{
+	switch ( value.type )
+	{
+		case FOOBAR_MATH_VALUE_INT:
+		{
+			mpz_t exp, integer, frac;
+			mpz_inits( exp, integer, frac, NULL );
+			mpz_ui_pow_ui( exp, 10, value.int_value.decimal_places );
+			mpz_mod( frac, value.int_value.v, exp );
+			mpz_div( integer, value.int_value.v, exp );
+			mpf_t f_exp, f_frac;
+			mpf_inits( f_exp, f_frac, NULL );
+			mpf_set_z( f_exp, exp );
+			mpf_set_z( f_frac, frac );
+			mpf_div( f_frac, f_frac, f_exp );
+			long double result = mpz_get_d( integer ) + mpf_get_d( f_frac );
+			mpf_clears( f_exp, f_frac, NULL );
+			mpz_clears( exp, integer, frac, NULL );
+			return result;
+		}
+		case FOOBAR_MATH_VALUE_FLOAT:
+			return value.float_value.v;
+		default:
+			g_warn_if_reached( );
+			return 0;
+	}
+}
diff --git a/src/services/quick-answers/math.h b/src/services/quick-answers/math.h
new file mode 100644
index 0000000..fafa73d
--- /dev/null
+++ b/src/services/quick-answers/math.h
@@ -0,0 +1,148 @@
+#pragma once
+
+#include <gio/gio.h>
+#include <gmp.h>
+
+G_BEGIN_DECLS
+
+typedef enum
+{
+	FOOBAR_MATH_VALUE_INT,
+	FOOBAR_MATH_VALUE_FLOAT,
+} FoobarMathValueType;
+
+typedef struct _FoobarMathValue FoobarMathValue;
+
+struct _FoobarMathValue
+{
+	FoobarMathValueType type;
+
+	union
+	{
+		struct
+		{
+			mpz_t v;
+			gsize decimal_places;
+		} int_value;
+
+		struct
+		{
+			long double v;
+		} float_value;
+	};
+};
+
+typedef enum
+{
+	FOOBAR_MATH_TOKEN_IDENTIFIER,
+	FOOBAR_MATH_TOKEN_NUMBER,
+	FOOBAR_MATH_TOKEN_PAREN_OPEN,
+	FOOBAR_MATH_TOKEN_PAREN_CLOSE,
+	FOOBAR_MATH_TOKEN_PLUS,
+	FOOBAR_MATH_TOKEN_MINUS,
+	FOOBAR_MATH_TOKEN_MUL,
+	FOOBAR_MATH_TOKEN_DIV,
+	FOOBAR_MATH_TOKEN_POW,
+} FoobarMathTokenType;
+
+typedef struct _FoobarMathToken FoobarMathToken;
+
+struct _FoobarMathToken
+{
+	FoobarMathTokenType type;
+	gchar const*        data;
+	gsize               length;
+};
+
+typedef enum
+{
+	FOOBAR_MATH_EXPRESSION_VALUE,
+	FOOBAR_MATH_EXPRESSION_FUNCTION,
+	FOOBAR_MATH_EXPRESSION_CONSTANT,
+	FOOBAR_MATH_EXPRESSION_OPERATION,
+} FoobarMathExpressionType;
+
+typedef enum
+{
+	FOOBAR_MATH_FUNCTION_NEGATE,
+	FOOBAR_MATH_FUNCTION_SIN,
+	FOOBAR_MATH_FUNCTION_COS,
+	FOOBAR_MATH_FUNCTION_SEC,
+	FOOBAR_MATH_FUNCTION_CSC,
+	FOOBAR_MATH_FUNCTION_TAN,
+	FOOBAR_MATH_FUNCTION_COT,
+	FOOBAR_MATH_FUNCTION_ARCSIN,
+	FOOBAR_MATH_FUNCTION_ARCCOS,
+	FOOBAR_MATH_FUNCTION_ARCSEC,
+	FOOBAR_MATH_FUNCTION_ARCCSC,
+	FOOBAR_MATH_FUNCTION_ARCTAN,
+	FOOBAR_MATH_FUNCTION_ARCCOT,
+	FOOBAR_MATH_FUNCTION_EXP,
+	FOOBAR_MATH_FUNCTION_SQRT,
+} FoobarMathFunction;
+
+typedef enum
+{
+	FOOBAR_MATH_CONSTANT_PI,
+	FOOBAR_MATH_CONSTANT_E,
+} FoobarMathConstant;
+
+typedef enum
+{
+	FOOBAR_MATH_OPERATION_ADD,
+	FOOBAR_MATH_OPERATION_SUB,
+	FOOBAR_MATH_OPERATION_MUL,
+	FOOBAR_MATH_OPERATION_DIV,
+	FOOBAR_MATH_OPERATION_POW,
+} FoobarMathOperation;
+
+typedef struct _FoobarMathExpression FoobarMathExpression;
+
+FoobarMathToken*      foobar_math_lex                     ( gchar const*                input,
+                                                            gsize                       input_length,
+                                                            gsize*                      out_count );
+FoobarMathExpression* foobar_math_parse                   ( FoobarMathToken const*      tokens,
+                                                            gsize                       tokens_count );
+FoobarMathExpression* foobar_math_expression_new_value    ( FoobarMathValue             value );
+FoobarMathExpression* foobar_math_expression_new_function ( FoobarMathFunction          function,
+                                                            FoobarMathExpression*       input );
+FoobarMathExpression* foobar_math_expression_new_constant ( FoobarMathConstant          constant );
+FoobarMathExpression* foobar_math_expression_new_operation( FoobarMathOperation         operation,
+                                                            FoobarMathExpression*       lhs,
+                                                            FoobarMathExpression*       rhs );
+void                  foobar_math_expression_print        ( FoobarMathExpression const* expr,
+                                                            gint                        indentation );
+gboolean              foobar_math_evaluate                ( FoobarMathExpression const* expr,
+                                                            FoobarMathValue*            out_value );
+void                  foobar_math_expression_free         ( FoobarMathExpression*       expression );
+void                  foobar_math_value_new_int           ( FoobarMathValue*            out_value );
+void                  foobar_math_value_from_float        ( long double                 value,
+                                                            FoobarMathValue*            out_value );
+gboolean              foobar_math_value_from_string       ( gchar const*                input,
+                                                            gsize                       input_length,
+                                                            FoobarMathValue*            out_value );
+void                  foobar_math_value_copy              ( FoobarMathValue             value,
+                                                            FoobarMathValue*            out_value );
+void                  foobar_math_value_free              ( FoobarMathValue             value );
+void                  foobar_math_value_negate            ( FoobarMathValue*            value );
+gboolean              foobar_math_value_add               ( FoobarMathValue*            lhs,
+                                                            FoobarMathValue*            rhs,
+                                                            FoobarMathValue*            out_value );
+gboolean              foobar_math_value_sub               ( FoobarMathValue*            lhs,
+                                                            FoobarMathValue*            rhs,
+                                                            FoobarMathValue*            out_value );
+gboolean              foobar_math_value_mul               ( FoobarMathValue*            lhs,
+                                                            FoobarMathValue*            rhs,
+                                                            FoobarMathValue*            out_value );
+gboolean              foobar_math_value_div               ( FoobarMathValue*            lhs,
+                                                            FoobarMathValue*            rhs,
+                                                            FoobarMathValue*            out_value );
+gboolean              foobar_math_value_pow               ( FoobarMathValue*            lhs,
+                                                            FoobarMathValue*            rhs,
+                                                            FoobarMathValue*            out_value );
+gboolean              foobar_math_value_unify_integers    ( FoobarMathValue*            a,
+                                                            FoobarMathValue*            b );
+gchar*                foobar_math_value_to_string         ( FoobarMathValue             value );
+long double           foobar_math_value_to_float          ( FoobarMathValue             value );
+
+G_END_DECLS
diff --git a/src/services/quick-answers/math.test.c b/src/services/quick-answers/math.test.c
new file mode 100644
index 0000000..416b576
--- /dev/null
+++ b/src/services/quick-answers/math.test.c
@@ -0,0 +1,153 @@
+#include "services/quick-answers/math.h"
+#include <mutest.h>
+
+#define SERIALIZATION_TEST( value, identifier )                                                  \
+	static void serialization_value_##identifier##_spec( void )                                  \
+	{                                                                                            \
+		FoobarMathValue val;                                                                     \
+                                                                                                 \
+		gchar const input[] = #value;                                                            \
+		mutest_expect(                                                                           \
+			"parse result",                                                                      \
+			mutest_bool_value( foobar_math_value_from_string( input, sizeof(input) - 1, &val) ), \
+			mutest_to_be_true,                                                                   \
+			NULL );                                                                              \
+		g_autofree gchar* output = foobar_math_value_to_string( val );                           \
+		mutest_expect(                                                                           \
+			"string representation",                                                             \
+			mutest_string_value( output ),                                                       \
+			mutest_to_be,                                                                        \
+			input,                                                                               \
+			NULL );                                                                              \
+                                                                                                 \
+		foobar_math_value_free( val );                                                           \
+	}
+
+SERIALIZATION_TEST( 0, 0 )
+SERIALIZATION_TEST( 1, 1 )
+SERIALIZATION_TEST( -1, neg_1 )
+SERIALIZATION_TEST( 1.2, 1_2 )
+SERIALIZATION_TEST( -1.2, neg_1_2 )
+SERIALIZATION_TEST( 1.30002, 1_30002 )
+SERIALIZATION_TEST( -1.30002, neg_1_30002 )
+SERIALIZATION_TEST( 0.2, 0_2 )
+SERIALIZATION_TEST( -0.2, neg_0_2 )
+SERIALIZATION_TEST( 0.00002, 0_00002 )
+SERIALIZATION_TEST( -0.00002, neg_0_00002 )
+SERIALIZATION_TEST( 123, 123 )
+SERIALIZATION_TEST( 123.456, 123_456 )
+SERIALIZATION_TEST( -123, neg_123 )
+SERIALIZATION_TEST( -123.456, neg_123_456 )
+
+#undef SERIALIZATION_TEST
+
+static void serialization_suite( void )
+{
+	mutest_it( "value 0", serialization_value_0_spec );
+	mutest_it( "value 1", serialization_value_1_spec );
+	mutest_it( "value -1", serialization_value_neg_1_spec );
+	mutest_it( "value 1.2", serialization_value_1_2_spec );
+	mutest_it( "value -1.2", serialization_value_neg_1_2_spec );
+	mutest_it( "value 1.30002", serialization_value_1_30002_spec );
+	mutest_it( "value -1.30002", serialization_value_neg_1_30002_spec );
+	mutest_it( "value 0.2", serialization_value_0_2_spec );
+	mutest_it( "value -0.2", serialization_value_neg_0_2_spec );
+	mutest_it( "value 0.00002", serialization_value_0_00002_spec );
+	mutest_it( "value -0.00002", serialization_value_neg_0_00002_spec );
+	mutest_it( "value 123", serialization_value_123_spec );
+	mutest_it( "value 123.456", serialization_value_123_456_spec );
+	mutest_it( "value -123", serialization_value_neg_123_spec );
+	mutest_it( "value -123.456", serialization_value_neg_123_456_spec );
+}
+#define OPERATION_TEST( op, value_a, value_b, value_res, identifier )                              \
+	static void operation_##identifier##_spec( void )                                              \
+	{                                                                                              \
+		FoobarMathValue a, b, res;                                                                 \
+                                                                                                   \
+		gchar const input_a[] = #value_a;                                                          \
+		gchar const input_b[] = #value_b;                                                          \
+		mutest_expect(                                                                             \
+			"input a parsed",                                                                      \
+			mutest_bool_value( foobar_math_value_from_string( input_a, sizeof(input_a) - 1, &a) ), \
+			mutest_to_be_true,                                                                     \
+			NULL );                                                                                \
+		mutest_expect(                                                                             \
+			"input b parsed",                                                                      \
+			mutest_bool_value( foobar_math_value_from_string( input_b, sizeof(input_b) - 1, &b) ), \
+			mutest_to_be_true,                                                                     \
+			NULL );                                                                                \
+		foobar_math_value_##op( &a, &b, &res );                                                    \
+		g_autofree gchar* output = foobar_math_value_to_string( res );                             \
+		mutest_expect(                                                                             \
+			"result",                                                                              \
+			mutest_string_value( output ),                                                         \
+			mutest_to_be,                                                                          \
+			#value_res,                                                                            \
+			NULL );                                                                                \
+                                                                                                   \
+		foobar_math_value_free( a );                                                               \
+		foobar_math_value_free( b );                                                               \
+		foobar_math_value_free( res );                                                             \
+	}
+
+OPERATION_TEST( add, 123, 456, 579, 123_plus_456)
+OPERATION_TEST( add, 123.456, 11, 134.456, 123_456_plus_11)
+OPERATION_TEST( add, 11, 123.456, 134.456, 11_plus_123_456)
+OPERATION_TEST( sub, 123, 456, -333, 123_minus_456)
+OPERATION_TEST( sub, 123.456, 11, 112.456, 123_456_minus_11)
+OPERATION_TEST( sub, 11, 123.456, -112.456, 11_minus_123_456)
+OPERATION_TEST( mul, 123, 3, 369, 123_times_3 )
+OPERATION_TEST( mul, 12, 0.05, 0.6, 12_times_0_05 )
+OPERATION_TEST( mul, 0.05, 12, 0.6, 0_05_times_12 )
+OPERATION_TEST( div, 369, 3, 123, 369_div_3 )
+OPERATION_TEST( div, 369, 2, 184.5, 369_div_2 )
+OPERATION_TEST( div, 12, 0.05, 240, 12_div_0_05 )
+OPERATION_TEST( div, 0.08, 4, 0.02, 0_08_div_4 )
+OPERATION_TEST( pow, 2, 3, 8, 2_pow_3 )
+OPERATION_TEST( pow, 4, 0.5, 2, 4_pow_0_5 )
+
+#undef OPERATION_TEST
+
+static void addition_suite( void )
+{
+	mutest_it( "calculate 123 + 456", operation_123_plus_456_spec );
+	mutest_it( "calculate 123.456 + 11", operation_123_456_plus_11_spec );
+	mutest_it( "calculate 11 + 123.456", operation_11_plus_123_456_spec );
+}
+
+static void subtraction_suite( void )
+{
+	mutest_it( "calculate 123 - 456", operation_123_minus_456_spec );
+	mutest_it( "calculate 123.456 - 11", operation_123_456_minus_11_spec );
+	mutest_it( "calculate 11 - 123.456", operation_11_minus_123_456_spec );
+}
+
+static void multiplication_suite( void )
+{
+	mutest_it( "calculate 123 * 3", operation_123_times_3_spec );
+	mutest_it( "calculate 12 * 0.05", operation_12_times_0_05_spec );
+	mutest_it( "calculate 0.05 * 12", operation_0_05_times_12_spec );
+}
+
+static void division_suite( void )
+{
+	mutest_it( "calculate 369 / 3", operation_369_div_3_spec );
+	mutest_it( "calculate 369 / 2", operation_369_div_2_spec );
+	mutest_it( "calculate 12 / 0.05", operation_12_div_0_05_spec );
+	mutest_it( "calculate 0.08 / 4", operation_0_08_div_4_spec );
+}
+
+static void power_suite( void )
+{
+	mutest_it( "calculate 2 ^ 3", operation_2_pow_3_spec );
+	mutest_it( "calculate 4 ^ 0.5", operation_4_pow_0_5_spec );
+}
+
+MUTEST_MAIN(
+	mutest_describe( "Serialization", serialization_suite );
+	mutest_describe( "Addition", addition_suite );
+	mutest_describe( "Subtraction", subtraction_suite );
+	mutest_describe( "Multiplication", multiplication_suite );
+	mutest_describe( "Division", division_suite );
+	mutest_describe( "Power", power_suite );
+)
diff --git a/src/services/quick-answers/meson.build b/src/services/quick-answers/meson.build
new file mode 100644
index 0000000..ae468c2
--- /dev/null
+++ b/src/services/quick-answers/meson.build
@@ -0,0 +1,9 @@
+foobar_sources += files(
+  'math-lexer.c',
+  'math-parser.c',
+  'math.c',
+)
+
+foobar_tests += {
+  'math': files('math.test.c'),
+}