infer var type when initializer is a number constant

examples/brainfuck.zr

@@ -2,11 +2,11 @@ func main[] : i64
     // https://brainfuck.org/sierpinski.b
     let src: str = "++++++++[>+>++++<<-]>++>>+<[-[>>+<<-]+>>]>+[-<<<[->[+[-]+>++>>>-<<]<[<]>>++++++[<<+++++>>-]+<<++.[-]<<]>.>+[>>]>+]"
     let src_len: i64 = str.len(src)
-    let i: i64 = 0
+    let i = 0
 
     let memory: ptr = mem.alloc(30000)
     mem.zero(memory, 30000)
-    let p: i64 = 0
+    let p = 0
 
     while i < src_len
         let op: u8 = src[i]
@@ -26,7 +26,7 @@ func main[] : i64
         else if op == '['
             if !memory[p]
                 i = i + 1
-                let opened: i64 = 0
+                let opened = 0
                 while i < src_len & !(src[i] == ']' & !opened)
                     if src[i] == '['
                         opened = opened + 1
@@ -36,7 +36,7 @@ func main[] : i64
         else if op == ']'
             if memory[p]
                 i = i - 1
-                let closed: i64 = 0
+                let closed = 0
                 while i >= 0 & !(src[i] == '[' & !closed)
                     if src[i] == ']'
                         closed = closed + 1