add: start basic work on the lexer

1 files changed, 136 insertions, 0 deletions

diff --git a/src/lexer/lexer.c b/src/lexer/lexer.c
new file mode 100644
index 0000000..7c5ca8f
--- /dev/null
+++ b/src/lexer/lexer.c
@@ -0,0 +1,136 @@
+#include <stdbool.h>
+
+#include "lexer/lexer.h"
+
+static bool is_alpha(char character)
+{
+	return (character >= 'a' && character <= 'z') || 
+		   (character >= 'A' && character <= 'Z') || 
+		    character == '_';
+}
+
+static bool is_digit(char character)
+{
+	return character >= '0' && character <= '9';
+}
+
+static char peek(struct Lexer* lexer)
+{
+	return *lexer->current;
+}
+
+static char advance(struct Lexer* lexer)
+{
+	char c = *lexer->current;
+	lexer->current += 1;
+	return c;
+}
+
+static void skip_whitespace(struct Lexer* lexer)
+{
+	for (;;)
+	{
+		char c = peek(lexer);
+		if (c == ' ' || c == '\t' || c == '\r')
+			advance(lexer);
+		else if (c == '\n')
+		{
+			lexer->line += 1;
+			advance(lexer);
+		}
+		else
+			return;
+	}
+}
+
+static struct Token make_token(struct Lexer* lexer, enum TokenType type, const char* start)
+{
+	struct Token token;
+	token.type = type;
+	token.start = start;
+	token.length = (size_t)(lexer->current - start);
+	token.line = lexer->line;
+	return token;
+}
+
+struct Lexer create_lexer(const char* source)
+{
+	struct Lexer lexer;
+	lexer.source = source;
+	lexer.current = source;
+	lexer.line = 1;
+	return lexer;
+}
+
+struct Token scan_token(struct Lexer* lexer)
+{
+	skip_whitespace(lexer);
+
+	const char* start = lexer->current;
+	if (peek(lexer) == '\0')
+		return make_token(lexer, TOKEN_EOF, start);
+	char character = advance(lexer);
+
+	if (is_alpha(character))
+	{
+		while (is_alpha(peek(lexer)) || is_digit(peek(lexer)))
+			advance(lexer);
+		return make_token(lexer, TOKEN_IDENTIFIER, start);
+	}
+
+	if (is_digit(character))
+	{
+		while (is_digit(peek(lexer)))
+			advance(lexer);
+		return make_token(lexer, TOKEN_INTEGER, start);
+	}
+
+	switch (character)
+	{
+		case '=': return make_token(lexer, TOKEN_EQUAL,         start);
+		case '+': return make_token(lexer, TOKEN_PLUS,          start);
+		case '-': return make_token(lexer, TOKEN_MINUS,         start);
+		case '*': return make_token(lexer, TOKEN_STAR,          start);
+		case '/': return make_token(lexer, TOKEN_SLASH,         start);
+		case '^': return make_token(lexer, TOKEN_CARET,         start);
+		case '.': return make_token(lexer, TOKEN_DOT,           start);
+		case ',': return make_token(lexer, TOKEN_COMMA,         start);
+		case ':': return make_token(lexer, TOKEN_COLON,         start);
+		case '(': return make_token(lexer, TOKEN_LEFT_PAREN,    start);
+		case ')': return make_token(lexer, TOKEN_RIGHT_PAREN,   start);
+		case '[': return make_token(lexer, TOKEN_LEFT_BRACKET,  start);
+		case ']': return make_token(lexer, TOKEN_RIGHT_BRACKET, start);
+		case '{': return make_token(lexer, TOKEN_LEFT_BRACE,    start);
+		case '}': return make_token(lexer, TOKEN_RIGHT_BRACE,   start);
+	}
+
+	return make_token(lexer, TOKEN_UNKNOWN, start);
+}
+
+const char* token_type_name(enum TokenType type)
+{
+	switch (type)
+	{
+		case TOKEN_EOF:           return "eof";
+		case TOKEN_IDENTIFIER:    return "identifier";
+		case TOKEN_INTEGER:       return "integer";
+		case TOKEN_EQUAL:         return "equal";
+		case TOKEN_PLUS:          return "plus";
+		case TOKEN_MINUS:         return "minus";
+		case TOKEN_STAR:          return "star";
+		case TOKEN_SLASH:         return "slash";
+		case TOKEN_CARET:         return "caret";
+		case TOKEN_DOT:           return "dot";
+		case TOKEN_COMMA:         return "comma";
+		case TOKEN_COLON:         return "colon";
+		case TOKEN_LEFT_PAREN:    return "left_paren";
+		case TOKEN_RIGHT_PAREN:   return "right_paren";
+		case TOKEN_LEFT_BRACKET:  return "left_bracket";
+		case TOKEN_RIGHT_BRACKET: return "right_bracket";
+		case TOKEN_LEFT_BRACE:    return "left_brace";
+		case TOKEN_RIGHT_BRACE:   return "right_brace";
+		case TOKEN_UNKNOWN:       return "unknown";
+	}
+
+	return "unknown";
+}