add: top level parser

1 files changed, 86 insertions, 0 deletions

diff --git a/src/parser/parser.c b/src/parser/parser.c
new file mode 100644
index 0000000..5845ad4
--- /dev/null
+++ b/src/parser/parser.c
@@ -0,0 +1,86 @@
+#include <stdio.h>
+
+#include "parser/parser.h"
+
+struct Parser
+{
+	struct Lexer* lexer;
+	struct Token current;
+	struct Token previous;
+	bool had_error;
+};
+
+static void advance_parser(struct Parser* parser)
+{
+	parser->previous = parser->current;
+	parser->current = scan_token(parser->lexer);
+}
+
+static bool check(struct Parser* parser, enum TokenType type)
+{
+	return parser->current.type == type;
+}
+
+static void error_at(struct Parser* parser, struct Token token, const char* message)
+{
+	fprintf(stderr, "error: line %u: %s\n", token.line, message);
+	parser->had_error = true;
+}
+
+static bool consume(struct Parser* parser, enum TokenType type, const char* message)
+{
+	if (check(parser, type))
+	{
+		advance_parser(parser);
+		return true;
+	}
+
+	error_at(parser, parser->current, message);
+	return false;
+}
+
+static bool parse_const(struct Parser* parser, struct Program* program)
+{
+	struct ConstDecl decl;
+
+	if (!consume(parser, TOKEN_IDENTIFIER, "expected constant name after 'const'"))
+		return false;
+	decl.name = parser->previous;
+
+	if (!consume(parser, TOKEN_EQUAL, "expected '=' after constant name"))
+		return false;
+
+	if (!consume(parser, TOKEN_INTEGER, "expected integer value after '='"))
+		return false;
+	decl.value = parser->previous;
+
+	add_const(program, decl);
+	return true;
+}
+
+bool parse_program(struct Lexer* lexer, struct Program* out)
+{
+	struct Parser parser;
+	parser.lexer = lexer;
+	parser.had_error = false;
+	advance_parser(&parser);
+
+	*out = create_program();
+
+	while (!check(&parser, TOKEN_EOF))
+	{
+		if (check(&parser, TOKEN_CONST))
+		{
+			advance_parser(&parser);
+			if (!parse_const(&parser, out))
+				return false;
+		}
+		else
+		{
+			error_at(&parser, parser.current, "expected a top-level declaration");
+			return false;
+		}
+	}
+
+	return !parser.had_error;
+}