parser: Introduce statement keywords

This commit introduces a few changes in pipalang syntax. Now, both
functions and variables requires keywords to be defined.

before:

  main(): i32 {
    a: i32 = 2;
    return a;
  }

now:

  fn main(): i32 {
    let a: i32 = 2;
    return a;
  }

Signed-off-by: Carlos Maniero <carlos@maniero.me>
Reviewed-by: Johnny Richard <johnny@johnnyrichard.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/lexer.c b/src/lexer.c
index 3f6948a..56e24af 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -97,10 +97,18 @@ lexer_tokenize_name(lexer_t *lexer, token_t *token)
 static void
 lexer_token_process_keyword(token_t *token)
 {
+  if (string_view_eq(string_view_from_str("let"), token->value)) {
+    token->kind = TOKEN_KEYWORD_LET;
+    return;
+  }
   if (string_view_eq(string_view_from_str("return"), token->value)) {
     token->kind = TOKEN_KEYWORD_RETURN;
     return;
   }
+  if (string_view_eq(string_view_from_str("fn"), token->value)) {
+    token->kind = TOKEN_KEYWORD_FN;
+    return;
+  }
 }
 
 void
@@ -318,6 +326,10 @@ token_kind_to_str(token_kind_t kind)
       return "=";
     case TOKEN_KEYWORD_RETURN:
       return "return";
+    case TOKEN_KEYWORD_FN:
+      return "fn";
+    case TOKEN_KEYWORD_LET:
+      return "let";
     case TOKEN_EOF:
       return "TOKEN_EOF";
     case TOKEN_UNKNOWN: