candidate increment/decrement implementation

src/parser.rs

@@ -152,6 +152,8 @@ pub enum Token {
     Fn,
     Break,
     Return,
+    PlusEquals,
+    MinusEquals,
     LexErr(LexError),
 }
 
@@ -350,8 +352,24 @@ impl<'a> Iterator for TokenIterator<'a> {
                 ')' => return Some(Token::RParen),
                 '[' => return Some(Token::LSquare),
                 ']' => return Some(Token::RSquare),
-                '+' => return Some(Token::Plus),
-                '-' => return Some(Token::Minus),
+                '+' => {
+                    return match self.char_stream.peek() {
+                        Some(&'=') => {
+                            self.char_stream.next();
+                            Some(Token::PlusEquals)
+                        },
+                        _ => Some(Token::Plus)
+                    }
+                },
+                '-' => {
+                    return match self.char_stream.peek() {
+                        Some(&'=') => {
+                            self.char_stream.next();
+                            Some(Token::MinusEquals)
+                        },
+                        _ => Some(Token::Minus)
+                    }
+                },
                 '*' => return Some(Token::Multiply),
                 '/' => return Some(Token::Divide),
                 ';' => return Some(Token::Semicolon),
@@ -427,7 +445,9 @@ pub fn lex(input: &str) -> TokenIterator {
 
 fn get_precedence(token: &Token) -> i32 {
     match *token {
-        Token::Equals => 10,
+        Token::Equals
+        | Token::PlusEquals
+        | Token::MinusEquals => 10,
         Token::Or => 11,
         Token::And => 12,
         Token::LessThan
@@ -609,6 +629,20 @@ fn parse_binop<'a>(input: &mut Peekable<TokenIterator<'a>>,
                 Token::Multiply => Expr::FnCall("*".to_string(), vec![lhs_curr, rhs]),
                 Token::Divide => Expr::FnCall("/".to_string(), vec![lhs_curr, rhs]),
                 Token::Equals => Expr::Assignment(Box::new(lhs_curr), Box::new(rhs)),
+                Token::PlusEquals  => {
+                    let lhs_copy = lhs_curr.clone();
+                    Expr::Assignment(
+                        Box::new(lhs_curr),
+                        Box::new(Expr::FnCall("+".to_string(), vec![lhs_copy, rhs]))
+                    )
+                },
+                Token::MinusEquals  => {
+                    let lhs_copy = lhs_curr.clone();
+                    Expr::Assignment(
+                        Box::new(lhs_curr),
+                        Box::new(Expr::FnCall("-".to_string(), vec![lhs_copy, rhs]))
+                    )
+                },
                 Token::Period => Expr::Dot(Box::new(lhs_curr), Box::new(rhs)),
                 Token::EqualTo => Expr::FnCall("==".to_string(), vec![lhs_curr, rhs]),
                 Token::NotEqualTo => Expr::FnCall("!=".to_string(), vec![lhs_curr, rhs]),

src/tests.rs

@@ -401,3 +401,37 @@ fn test_array_with_structs() {
         assert!(false);
     }
 }
+
+#[test]
+fn test_increment() {
+    let mut engine = Engine::new();
+
+    if let Ok(result) = engine.eval::<i64>("let x = 1; x += 2; x") {
+        assert_eq!(result, 3);
+    } else {
+        assert!(false);
+    }
+
+    if let Ok(result) = engine.eval::<String>("let s = \"test\"; s += \"ing\"; s") {
+        assert_eq!(result, "testing".to_owned());
+    } else {
+        assert!(false);
+    }
+}
+
+#[test]
+fn test_decrement() {
+    let mut engine = Engine::new();
+
+    if let Ok(result) = engine.eval::<i64>("let x = 10; x -= 7; x") {
+        assert_eq!(result, 3);
+    } else {
+        assert!(false);
+    }
+
+    if let Ok(_) = engine.eval::<String>("let s = \"test\"; s -= \"ing\"; s") {
+        assert!(false);
+    } else {
+        assert!(true);
+    }
+}