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, 1 insertions, 1 deletions

diff --git a/examples/arithmetics.pipa b/examples/arithmetics.pipa
index e2b7645..f2449b8 100644
--- a/examples/arithmetics.pipa
+++ b/examples/arithmetics.pipa
@@ -1,3 +1,3 @@
-main(): i32 {
+fn main(): i32 {
   return ((2 + 1) * (5 - 3) + 7) * 2 / 2;
 }