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, 2 insertions, 0 deletions

diff --git a/src/lexer.h b/src/lexer.h
index 9aa8efe..6449a0a 100644
--- a/src/lexer.h
+++ b/src/lexer.h
@@ -38,6 +38,8 @@ typedef enum
   TOKEN_SLASH,
   TOKEN_EQUAL,
   TOKEN_KEYWORD_RETURN,
+  TOKEN_KEYWORD_FN,
+  TOKEN_KEYWORD_LET,
   TOKEN_EOF,
   TOKEN_UNKNOWN
 } token_kind_t;