From 2a014fd2107e7566f9b5d7b5abc96b53e3ea960e Mon Sep 17 00:00:00 2001
From: Daniel M <daniel.q.mueller@stud.h-da.de>
Date: Fri, 28 Jan 2022 19:34:31 +0100
Subject: [PATCH] Implement while loop

---
 src/interpreter.rs | 14 +++++++++++++-
 src/lexer.rs       | 12 ++++++++++++
 src/parser.rs      | 39 ++++++++++++++++++++++++++++++++++-----
 3 files changed, 59 insertions(+), 6 deletions(-)

diff --git a/src/interpreter.rs b/src/interpreter.rs
index 4ca6132..d426f7a 100644
--- a/src/interpreter.rs
+++ b/src/interpreter.rs
@@ -29,6 +29,18 @@ impl Interpreter {
                     let result = self.resolve_expr(rhs);
                     self.vartable.insert(name, result);
                 },
+                Stmt::While(condition, body) => {
+                    loop {
+                        // Check condition
+                        match self.resolve_expr(condition.clone()) {
+                            Value::I64(val) if val == 0 => break,
+                            Value::I64(_) => (),
+                        }
+
+                        // Execute loop body
+                        self.run(body.clone());
+                    }
+                }
             }
         }
     }
@@ -59,7 +71,7 @@ impl Interpreter {
                 _ => panic!("Runtime error: Left hand side of assignment must be an identifier"),
             }
         }
-        
+
 
         let lhs = self.resolve_expr(lhs);
         let rhs = self.resolve_expr(rhs);
diff --git a/src/lexer.rs b/src/lexer.rs
index e281f9a..90d7a10 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -13,12 +13,21 @@ pub enum Token {
     /// Right parentheses (')')
     RParen,
 
+    /// Left brace ({)
+    LBrace,
+
+    /// Right brace (})
+    RBrace,
+
     /// Identifier (variable / function / ... name)
     Ident(String),
 
     /// Let identifier (let)
     Let,
 
+    /// While (while)
+    While,
+
     /// Assignment (single equal) (=)
     Assign,
 
@@ -158,6 +167,8 @@ impl<'a> Lexer<'a> {
                 '>' => tokens.push(Token::Gt),
                 '=' => tokens.push(Token::Assign),
                 ';' => tokens.push(Token::Semicolon),
+                '{' => tokens.push(Token::LBrace),
+                '}' => tokens.push(Token::RBrace),
 
                 'a'..='z' | 'A'..='Z' | '_' => {
                     let mut ident = String::from(ch);
@@ -172,6 +183,7 @@ impl<'a> Lexer<'a> {
                         "true" => tokens.push(Token::I64(1)),
                         "false" => tokens.push(Token::I64(0)),
                         "let" => tokens.push(Token::Let),
+                        "while" => tokens.push(Token::While),
                         _ => tokens.push(Token::Ident(ident)),
                     }
                 }
diff --git a/src/parser.rs b/src/parser.rs
index 87a03fe..020f60d 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -73,6 +73,7 @@ pub struct Ast {
 pub enum Stmt {
     Expr(Expr),
     Let(String, Expr),
+    While(Expr, Ast),
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]
@@ -104,7 +105,8 @@ expr = expr_bor
 ## Statements
 stmt_expr = expr
 stmt_let = "let" IDENT "=" expr
-stmt = stmt_expr | stmt_let (";")*
+stmt_while = "while" expr "{" (stmt)* "}"
+stmt = stmt_expr | stmt_let | stmt_while
 */
 
 struct Parser<T: Iterator<Item = Token>> {
@@ -128,17 +130,39 @@ impl<T: Iterator<Item = Token>> Parser<T> {
                     continue;
                 }
                 Token::EoF => break,
+                Token::RBrace => break,
                 Token::Let => self.parse_let_stmt(),
+                Token::While => self.parse_while(),
                 // By default try to parse an expression
                 _ => Stmt::Expr(self.parse_expr()),
             };
 
             prog.push(stmt);
         }
-        
+
         Ast { prog }
     }
 
+    fn parse_while(&mut self) -> Stmt {
+        if !matches!(self.next(), Token::While) {
+            panic!("Error parsing while: Expected while token");
+        }
+
+        let condition = self.parse_expr();
+
+        if !matches!(self.next(), Token::LBrace) {
+            panic!("Error parsing while: Expected '{{' token");
+        }
+
+        let body = self.parse();
+
+        if !matches!(self.next(), Token::RBrace) {
+            panic!("Error parsing while: Expected '}}' token");
+        }
+
+        Stmt::While(condition, body)
+    }
+
     fn parse_let_stmt(&mut self) -> Stmt {
         if !matches!(self.next(), Token::Let) {
             panic!("Error parsing let: Expected let token");
@@ -257,8 +281,11 @@ impl BinOpType {
 
 #[cfg(test)]
 mod tests {
-    use super::{parse, Expr, BinOpType};
-    use crate::{lexer::Token, parser::{Stmt, Ast}};
+    use super::{parse, BinOpType, Expr};
+    use crate::{
+        lexer::Token,
+        parser::{Ast, Stmt},
+    };
 
     #[test]
     fn test_parser() {
@@ -285,7 +312,9 @@ mod tests {
             Expr::I64(4).into(),
         );
 
-        let expected = Ast { prog: vec![Stmt::Expr(expected)] };
+        let expected = Ast {
+            prog: vec![Stmt::Expr(expected)],
+        };
 
         let actual = parse(tokens);
         assert_eq!(expected, actual);