Implement loop keyword

- Loop is a combination of `while` and `for`
- `loop cond { }` acts exactly like `while`
- `loop cond; advance { }` acts like `for` without init

src/interpreter.rs

@@ -40,6 +40,21 @@ impl Interpreter {
                     let result = self.resolve_expr(expr);
                     println!("Result = {:?}", result);
                 }
+
+                Statement::Loop(lop) => {
+                    // loop runs as long condition != 0
+                    loop {
+                        if matches!(self.resolve_expr(lop.condition.clone()), Value::I64(0)) {
+                            break;
+                        }
+
+                        self.run(lop.body.clone());
+
+                        if let Some(adv) = &lop.advancement {
+                            self.resolve_expr(adv.clone());
+                        }
+                    }
+                }
             }
 
         }

src/lexer.rs

@@ -10,12 +10,20 @@ pub enum Token {
     /// Identifier (name for variables, functions, ...)
     Ident(String),
 
+    Loop,
+
     /// Left Parenthesis ('(')
     LParen,
 
     /// Right Parenthesis (')')
     RParen,
 
+    /// Left curly braces ({)
+    LBraces,
+
+    /// Right curly braces (})
+    RBraces,
+
     /// Plus (+)
     Add,
 
@@ -147,6 +155,8 @@ impl<'a> Lexer<'a> {
                 '<' => tokens.push(Token::LAngle),
                 '>' => tokens.push(Token::RAngle),
                 '=' => tokens.push(Token::Equ),
+                '{' => tokens.push(Token::LBraces),
+                '}' => tokens.push(Token::RBraces),
 
                 // Lex numbers
                 ch @ '0'..='9' => {
@@ -187,7 +197,12 @@ impl<'a> Lexer<'a> {
                         }
                     }
 
-                    tokens.push(Token::Ident(ident));
+                    let token = match ident.as_str() {
+                        "loop" => Token::Loop,
+                        _ => Token::Ident(ident),
+                    };
+
+                    tokens.push(token);
                 }
 
                 //TODO: Don't panic, keep calm

src/parser.rs

@@ -81,9 +81,20 @@ pub enum Expression {
     UnOp(UnOpType, Box<Expression>),
 }
 
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct Loop {
+    /// The condition that determines if the loop should continue
+    pub condition: Expression,
+    /// This is executed after each loop to advance the condition variables
+    pub advancement: Option<Expression>,
+    /// The loop body that is executed each loop
+    pub body: Ast,
+}
+
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum Statement {
     Expr(Expression),
+    Loop(Loop),
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]
@@ -111,6 +122,10 @@ impl<T: Iterator<Item = Token>> Parser<T> {
                     self.next();
                 }
                 Token::EoF => break,
+                Token::RBraces => {
+                    self.next();
+                    break;
+                }
 
                 // By default try to lex a statement
                 _ => {
@@ -124,14 +139,59 @@ impl<T: Iterator<Item = Token>> Parser<T> {
     }
 
     fn parse_stmt(&mut self) -> Statement {
-        let expr = self.parse_expr();
+        match self.peek() {
+            Token::Loop => Statement::Loop(self.parse_loop()),
 
-        // After a statement, there must be a semicolon
-        if !matches!(self.next(), Token::Semicolon) {
-            panic!("Expected semicolon after statement");
+            // If it is not a loop, try to lex as an expression
+            _ => {
+                let stmt = Statement::Expr(self.parse_expr());
+
+                // After a statement, there must be a semicolon
+                if !matches!(self.next(), Token::Semicolon) {
+                    panic!("Expected semicolon after statement");
+                }
+
+                stmt
+            }
+        }
+    }
+
+    // loop i < 1_000; i = i +1 {
+    //     if i % 3 == 0 | i % 5 == 0 {
+    //         sum = sum + i;
+    //     }
+    // }
+
+    fn parse_loop(&mut self) -> Loop {
+        if !matches!(self.next(), Token::Loop) {
+            panic!("Error lexing loop: Expected loop token");
         }
 
-        Statement::Expr(expr)
+        let condition = self.parse_expr();
+        let mut advancement = None;
+
+        let body;
+
+        match self.next() {
+            Token::LBraces => {
+                body = self.parse();
+            }
+
+            Token::Semicolon => {
+                advancement = Some(self.parse_expr());
+
+                if !matches!(self.next(), Token::LBraces) {
+                    panic!("Error lexing loop: Expected '{{'")
+                }
+
+                body = self.parse();
+            },
+
+            _ => panic!("Error lexing loop: Expected ';' or '{{'")
+        }
+
+        Loop { condition, advancement, body }
+
     }
 
     fn parse_expr(&mut self) -> Expression {
@@ -228,16 +288,16 @@ impl BinOpType {
 
     fn precedence(&self) -> u8 {
         match self {
-            BinOpType::BOr => 0,
-            BinOpType::BXor => 1,
-            BinOpType::BAnd => 2,
-            BinOpType::EquEqu | BinOpType::NotEqu => 3,
-            BinOpType::Less | BinOpType::LessEqu | BinOpType::Greater | BinOpType::GreaterEqu => 4,
-            BinOpType::Shl | BinOpType::Shr => 5,
-            BinOpType::Add | BinOpType::Sub => 6,
-            BinOpType::Mul | BinOpType::Div | BinOpType::Mod => 7,
-            BinOpType::Assign => 8,
-            BinOpType::Declare => 9,
+            BinOpType::Declare => 0,
+            BinOpType::Assign => 1,
+            BinOpType::BOr => 2,
+            BinOpType::BXor => 3,
+            BinOpType::BAnd => 4,
+            BinOpType::EquEqu | BinOpType::NotEqu => 5,
+            BinOpType::Less | BinOpType::LessEqu | BinOpType::Greater | BinOpType::GreaterEqu => 6,
+            BinOpType::Shl | BinOpType::Shr => 7,
+            BinOpType::Add | BinOpType::Sub => 8,
+            BinOpType::Mul | BinOpType::Div | BinOpType::Mod => 9,
         }
     }
 }