Allow uninitialized variables

TODO

@@ -1,5 +1,4 @@
 # Bugs
-- Uninitialized variables don't compile
 - stdlib moves line of file, which makes error reporting impossible
 
 # Features 

examples/playground.sb

@@ -1,4 +1,6 @@
 fn main() {
-    let x: string = "Hello World\n"
+    let x: string
+
+    x = "Hello World"
     _printf(x)
 }

src/parser/rules.rs

@@ -366,9 +366,17 @@ impl Parser {
             TokenKind::Colon => Some(self.parse_type()?),
             _ => None,
         };
+
+        match self.peek()?.kind {
+            TokenKind::Assign => {
                 self.match_token(TokenKind::Assign)?; 
                 let expr = self.parse_expression()?;
                 Ok(Statement::Declare(Variable { name, ty }, Some(expr)))
+            },
+            _ => {
+                Ok(Statement::Declare(Variable {name, ty}, None)) 
+            }
+        }
     }
 
     fn parse_assignent(&mut self, name: Option<Expression>) -> Result<Statement, String> {

src/parser/tests.rs

@@ -621,3 +621,23 @@ fn test_booleans_in_function_call() {
     let tree = parse(tokens, Some(raw.to_string()));
     assert!(tree.is_ok());
 }
+
+#[test]
+fn test_late_initializing_variable() {
+    let raw = "
+    fn main() {
+        let x: int
+        let y: string
+        x = 5
+        if x > 2 {
+            y = 'test'
+        }
+
+        _printf(x)
+        _printf(y)
+    }
+    ";
+    let tokens = tokenize(raw);
+    let tree = parse(tokens, Some(raw.to_string()));
+    assert!(tree.is_ok());
+}