Inline next token advance

1 files changed, 16 insertions, 15 deletions

diff --git a/rust/src/parser.rs b/rust/src/parser.rs
index 11948c1..c85a425 100644
--- a/rust/src/parser.rs
+++ b/rust/src/parser.rs
@@ -14,7 +14,7 @@ struct Parser {
 }
 
 impl Parser {
-    fn expect(&self, token: Token) -> Result<(), String> {
+    fn expect(&mut self, token: Token) -> Result<(), String> {
         if self.tokens.get(self.index) == Some(&token) {
             Ok(())
         } else {
@@ -24,14 +24,9 @@ impl Parser {
                 self.tokens.get(self.index)
             ))
         }
-    }
-
-    fn next(&mut self) {
-        self.index += 1;
-    }
-
-    fn backtrack(&mut self) {
-        self.index -= 1;
+        .map(|_| {
+            self.next();
+        })
     }
 
     fn expect_symbol(&mut self) -> Result<String, String> {
@@ -40,6 +35,18 @@ impl Parser {
         } else {
             Err("Expected a symbol".to_string())
         }
+        .map(|s| {
+            self.next();
+            s
+        })
+    }
+
+    fn next(&mut self) {
+        self.index += 1;
+    }
+
+    fn backtrack(&mut self) {
+        self.index -= 1;
     }
 }
 
@@ -59,32 +66,26 @@ fn parse_expression(parser: &mut Parser) -> Result<Value, String> {
 
 fn parse_abstraction(parser: &mut Parser) -> Result<Value, String> {
     parser.expect(Token::LParen)?;
-    parser.next();
     parser.expect(Token::Lambda).map_err(|e| {
         parser.backtrack();
         e.to_string()
     })?;
-    parser.next();
     let var = parse_variable(parser)?;
     let body = parse_expression(parser)?;
     parser.expect(Token::RParen)?;
-    parser.next();
     Ok(Value::Lam(var, Box::new(body)))
 }
 
 fn parse_variable(parser: &mut Parser) -> Result<String, String> {
     let var = parser.expect_symbol()?;
-    parser.next();
     Ok(var)
 }
 
 fn parse_application(parser: &mut Parser) -> Result<Value, String> {
     parser.expect(Token::LParen)?;
-    parser.next();
     let left = parse_expression(parser)?;
     let right = parse_expression(parser)?;
     parser.expect(Token::RParen)?;
-    parser.next();
     Ok(Value::App(Box::new(left), Box::new(right)))
 }