From 1af3d14f3f995645a0de08a54b244c19840709e9 Mon Sep 17 00:00:00 2001 From: Hannes Schulze Date: Thu, 19 Jun 2025 23:17:58 +0200 Subject: init hs project --- csrc/services/quick-answers/math-lexer.c | 248 +++++++++++++++++++++++++++++++ 1 file changed, 248 insertions(+) create mode 100644 csrc/services/quick-answers/math-lexer.c (limited to 'csrc/services/quick-answers/math-lexer.c') diff --git a/csrc/services/quick-answers/math-lexer.c b/csrc/services/quick-answers/math-lexer.c new file mode 100644 index 0000000..7fbe877 --- /dev/null +++ b/csrc/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 ); +} -- cgit v1.3.1