Put expect into early return macro

src/parser.rs

@@ -17,20 +17,26 @@ pub enum ParseResult {
     Err(String)
 }
 
+macro_rules! expect {
+    ($tok:expr, $tokens:expr) => ( if !expect_token($tok, $tokens) {
+        println!("yo hitting");
+        return ParseResult::Err(format!("Expected {:?}", $tok));
+    })
+}
+
 pub fn parse(input: Vec<Token>) -> ParseResult {
 
     let mut tokens = input.iter();
 
     if let ParseResult::Ok(ast) = let_expression(&mut tokens) {
-        if expect(EOF, &mut tokens) {
+        expect!(EOF, &mut tokens);
         return ParseResult::Ok(ast);
     }
-    }
 
     return ParseResult::Err("Bad parse".to_string());
 }
 
-fn expect(tok: Token, tokens: &mut Iter<Token>) -> bool {
+fn expect_token(tok: Token, tokens: &mut Iter<Token>) -> bool {
     if let Some(n) = tokens.next() {
         let next = (*n).clone();
         return match (tok, next) {
@@ -50,7 +56,7 @@ fn expect(tok: Token, tokens: &mut Iter<Token>) -> bool {
 }
 
 fn let_expression<'a>(input: &mut Iter<Token>) -> ParseResult {
-    if expect(Identifier("let".to_string()), input) {
+    expect!(Identifier("let".to_string()), input);
     if let Some(&Identifier(ref name)) = input.next() {
         if let Some(&Identifier(ref s)) = input.next() {
             if s == "=" {
@@ -72,7 +78,6 @@ fn let_expression<'a>(input: &mut Iter<Token>) -> ParseResult {
             }
         }
     }
-    }
 
     return ParseResult::Err("Bad parse".to_string());
 }