Make match_token_kind! macro preserve the token in case of error

src/parse.rs

@@ -43,15 +43,20 @@ pub fn parse_program<I: Iterator<Item = Token>, F: FnMut(ScriptError)>(
 
 macro_rules! match_token_kind {
     ($tokens_peekable: expr, $($p:pat),+) => {{
-        match $tokens_peekable.peek().map(|token| token.kind()) {
+        let peeked = $tokens_peekable.peek();
+        match peeked.map(|token| token.kind()) {
             $(
                 Some($p) => {
                     // consume the peeked token
                     let token = $tokens_peekable.next().unwrap();
-                    Some(token)
+                    Ok(token)
                 }
             )+
-            _ => None
+            Some(_kind) => {
+                // this must be valid, because peeked.map will only give None if this is None.
+                Err(Some(peeked.unwrap()))
+            },
+            _ => Err(None)
         }
     }};
 }
@@ -66,7 +71,7 @@ fn synchronize_to_next_statement<I: Iterator<Item = Token>>(iter: &mut I) {
 }
 
 fn parse_statement<I: Iterator<Item = Token>>(iter: &mut Peekable<I>) -> Result<Stmt, ParseError> {
-    if match_token_kind!(iter, TokenKind::Print).is_some() {
+    if match_token_kind!(iter, TokenKind::Print).is_ok() {
         parse_statement_containing_expression(iter, |expression| Stmt::Print { expression })
     } else {
         parse_statement_containing_expression(iter, |expression| Stmt::Expression { expression })
@@ -77,19 +82,13 @@ fn parse_statement_containing_expression<I: Iterator<Item = Token>, F: Fn(Expr)
     iter: &mut Peekable<I>,
     make_statement: F,
 ) -> Result<Stmt, ParseError> {
-    // Snatch the next token before we parse it, so we have line information
-    let next_token_line = iter.peek().map(Token::line);
     let expression = parse_expression(iter)?;
-    if match_token_kind!(iter, TokenKind::SemiColon).is_some() {
-        Ok(make_statement(expression))
-    } else {
-        Err(ParseError {
+    match_token_kind!(iter, TokenKind::SemiColon)
+        .map(|_semicolon| make_statement(expression))
+        .map_err(|maybe_token| ParseError {
             message: "Expected a ';' after expression".to_string(),
-            // this should always be valid, as the token must have existed if we successfully
-            // parsed some expression (there are no zero-token expressions)
-            line: Some(next_token_line.unwrap()),
+            line: maybe_token.map(Token::line),
         })
-    }
 }
 
 fn parse_expression<I: Iterator<Item = Token>>(iter: &mut Peekable<I>) -> Result<Expr, ParseError> {
@@ -146,7 +145,7 @@ fn parse_binary<I: Iterator<Item = Token>, F: Fn(&mut Peekable<I>) -> Result<Exp
 }
 
 fn parse_unary<I: Iterator<Item = Token>>(iter: &mut Peekable<I>) -> Result<Expr, ParseError> {
-    if let Some(token) = match_token_kind!(iter, TokenKind::Bang, TokenKind::Minus) {
+    if let Ok(token) = match_token_kind!(iter, TokenKind::Bang, TokenKind::Minus) {
         let operator = token;
         let right = parse_unary(iter)?;
         Ok(Expr::Unary {
@@ -193,7 +192,7 @@ fn parse_primary<I: Iterator<Item = Token>>(iter: &mut Peekable<I>) -> Result<Ex
             // consume the left paren
             iter.next();
             let expr = parse_expression(iter)?;
-            if match_token_kind!(iter, TokenKind::RightParen).is_some() {
+            if match_token_kind!(iter, TokenKind::RightParen).is_ok() {
                 Ok(Expr::Grouping {
                     expr: Box::new(expr),
                 })