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>

3 files changed, 8 insertions, 8 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;
 }
diff --git a/examples/main.pipa b/examples/main.pipa
index 6524bec..2da2231 100644
--- a/examples/main.pipa
+++ b/examples/main.pipa
@@ -1,3 +1,3 @@
-main(): i32 {
+fn main(): i32 {
   return 69;
 }
diff --git a/examples/variables.pipa b/examples/variables.pipa
index 0723782..3eabc73 100644
--- a/examples/variables.pipa
+++ b/examples/variables.pipa
@@ -1,10 +1,10 @@
-main(): i32 {
-  a: i32 = 13;
+fn main(): i32 {
+  let a: i32 = 13;
   a = a - 1;
-  b: i32 = 33;
+  let b: i32 = 33;
   b = 32;
-  c: i32 = 2 * (b + a);
-  d: i32 = (c - 33) + 1;
-  e: i32 = d;
+  let c: i32 = 2 * (b + a);
+  let d: i32 = (c - 33) + 1;
+  let e: i32 = d;
   return e / 2;
 }