parser: Refactor return statement to return an ast_node

During the refactoring process, I identified a memory leak where the
return argument was allocated but not freed in case of an error.

It also introduces the concept of keyword tokens. Where return is now a
keyword simplifying the parser.

Signed-off-by: Carlos Maniero <carlos@maniero.me>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/lexer.h b/src/lexer.h
index abee53a..70d4b0d 100644
--- a/src/lexer.h
+++ b/src/lexer.h
@@ -37,6 +37,7 @@ typedef enum
   TOKEN_STAR,
   TOKEN_SLASH,
   TOKEN_EQUAL,
+  TOKEN_KEYWORD_RETURN,
   TOKEN_EOF,
   TOKEN_UNKNOWN
 } token_kind_t;