add: parse conditional expressions

4 files changed, 114 insertions, 28 deletions

diff --git a/src/main.c b/src/main.c
index b40f90e..63f87fd 100644
--- a/src/main.c
+++ b/src/main.c
@@ -25,6 +25,41 @@ static void print_expr(struct Expr* expr)
 	}
 }
 
+static void print_statement(struct Statement* statement, const char* indent)
+{
+	switch (statement->kind)
+	{
+		case STATEMENT_ASSIGN:
+		{
+			struct AssignStatement assign = statement->assign;
+			printf("%s%s%.*s %.*s ", indent,
+				assign.target_deref ? "^" : "",
+				(int)assign.target.length, assign.target.start,
+				(int)assign.op.length, assign.op.start);
+			print_expr(assign.value);
+			printf("\n");
+			break;
+		}
+		case STATEMENT_LABEL:
+			printf("%s%.*s:\n", indent, (int)statement->label.name.length, statement->label.name.start);
+			break;
+		case STATEMENT_GOTO:
+			printf("%sgoto %.*s\n", indent, (int)statement->jump.label.length, statement->jump.label.start);
+			break;
+		case STATEMENT_SYSCALL:
+			printf("%ssyscall\n", indent);
+			break;
+		case STATEMENT_IF:
+			printf("%sif ", indent);
+			print_expr(statement->branch.left);
+			printf(" %.*s ", (int)statement->branch.comparison.length, statement->branch.comparison.start);
+			print_expr(statement->branch.right);
+			printf("\n");
+			print_statement(statement->branch.body, "    ");
+			break;
+	}
+}
+
 int main(int argc, char** argv)
 {
 	struct Args args;
@@ -79,32 +114,7 @@ int main(int argc, char** argv)
 		printf(")\n");
 
 		for (size_t s = 0; s < proc.body_count; s += 1)
-		{
-			struct Statement statement = proc.body[s];
-			switch (statement.kind)
-			{
-				case STATEMENT_ASSIGN:
-				{
-					struct AssignStatement assign = statement.assign;
-					printf("  %s%.*s %.*s ",
-						assign.target_deref ? "^" : "",
-						(int)assign.target.length, assign.target.start,
-						(int)assign.op.length, assign.op.start);
-					print_expr(assign.value);
-					printf("\n");
-					break;
-				}
-				case STATEMENT_LABEL:
-					printf("  %.*s:\n", (int)statement.label.name.length, statement.label.name.start);
-					break;
-				case STATEMENT_GOTO:
-					printf("  goto %.*s\n", (int)statement.jump.label.length, statement.jump.label.start);
-					break;
-				case STATEMENT_SYSCALL:
-					printf("  syscall\n");
-					break;
-			}
-		}
+			print_statement(&proc.body[s], "  ");
 	}
 
 	free_program(&program);
diff --git a/src/parser/ast.c b/src/parser/ast.c
index 97cdb6d..9bdf4d1 100644
--- a/src/parser/ast.c
+++ b/src/parser/ast.c
@@ -25,8 +25,20 @@ void free_expr(struct Expr* expr)
 
 static void free_statement(struct Statement* statement)
 {
-	if (statement->kind == STATEMENT_ASSIGN)
-		free_expr(statement->assign.value);
+	switch (statement->kind)
+	{
+		case STATEMENT_ASSIGN:
+			free_expr(statement->assign.value);
+			break;
+		case STATEMENT_IF:
+			free_expr(statement->branch.left);
+			free_expr(statement->branch.right);
+			free_statement(statement->branch.body);
+			free(statement->branch.body);
+			break;
+		default:
+			break;
+	}
 }
 
 void free_proc(struct ProcDecl* proc)
diff --git a/src/parser/ast.h b/src/parser/ast.h
index 199d802..e85e72f 100644
--- a/src/parser/ast.h
+++ b/src/parser/ast.h
@@ -65,6 +65,7 @@ enum StatementKind
 	STATEMENT_LABEL,
 	STATEMENT_GOTO,
 	STATEMENT_SYSCALL,
+	STATEMENT_IF,
 };
 
 struct AssignStatement
@@ -85,6 +86,14 @@ struct GotoStatement
 	struct Token label;
 };
 
+struct IfStatement
+{
+	struct Expr* left;
+	struct Token comparison;
+	struct Expr* right;
+	struct Statement* body;
+};
+
 struct Statement
 {
 	enum StatementKind kind;
@@ -93,6 +102,7 @@ struct Statement
 		struct AssignStatement assign;
 		struct LabelStatement label;
 		struct GotoStatement jump;
+		struct IfStatement branch;
 	};
 };
 
diff --git a/src/parser/parser.c b/src/parser/parser.c
index 5431bfd..2ae52f2 100644
--- a/src/parser/parser.c
+++ b/src/parser/parser.c
@@ -206,8 +206,62 @@ static struct Expr* parse_expression(struct Parser* parser)
 	return parse_binary(parser, parse_multiplicative, TOKEN_PLUS, TOKEN_MINUS);
 }
 
+static bool is_compare_op(enum TokenType type)
+{
+	return type == TOKEN_EQUAL_EQUAL
+		|| type == TOKEN_BANG_EQUAL
+		|| type == TOKEN_LESS
+		|| type == TOKEN_LESS_EQUAL
+		|| type == TOKEN_GREATER
+		|| type == TOKEN_GREATER_EQUAL;
+}
+
+static bool parse_statement(struct Parser* parser, struct Statement* out);
+
+static bool parse_if(struct Parser* parser, struct Statement* out)
+{
+	struct Expr* left = parse_expression(parser);
+	if (left == NULL)
+		return false;
+
+	if (!is_compare_op(parser->current.type))
+	{
+		error_at(parser, parser->current, "expected a comparison operator");
+		free_expr(left);
+		return false;
+	}
+	advance_parser(parser);
+	struct Token comparison = parser->previous;
+
+	struct Expr* right = parse_expression(parser);
+	if (right == NULL)
+	{
+		free_expr(left);
+		return false;
+	}
+
+	struct Statement* body = malloc(sizeof(struct Statement));
+	if (!parse_statement(parser, body))
+	{
+		free(body);
+		free_expr(left);
+		free_expr(right);
+		return false;
+	}
+
+	out->kind = STATEMENT_IF;
+	out->branch.left = left;
+	out->branch.comparison = comparison;
+	out->branch.right = right;
+	out->branch.body = body;
+	return true;
+}
+
 static bool parse_statement(struct Parser* parser, struct Statement* out)
 {
+	if (match_token(parser, TOKEN_IF))
+		return parse_if(parser, out);
+
 	if (match_token(parser, TOKEN_SYSCALL))
 	{
 		out->kind = STATEMENT_SYSCALL;