Implement if

src/interpreter.rs

@@ -1,6 +1,6 @@
 use std::{collections::HashMap, fmt::Display};
 
-use crate::{parser::{Expression, BinOpType, UnOpType, Ast, Statement, parse}, lexer::lex};
+use crate::{parser::{Expression, BinOpType, UnOpType, Ast, Statement, parse, If}, lexer::lex};
 
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum Value {
@@ -40,16 +40,16 @@ impl Interpreter {
                     self.resolve_expr(expr);
                 }
 
-                Statement::Loop(lop) => {
+                Statement::Loop(looop) => {
                     // loop runs as long condition != 0
                     loop {
-                        if matches!(self.resolve_expr(lop.condition.clone()), Value::I64(0)) {
+                        if matches!(self.resolve_expr(looop.condition.clone()), Value::I64(0)) {
                             break;
                         }
 
-                        self.run(lop.body.clone());
+                        self.run(looop.body.clone());
 
-                        if let Some(adv) = &lop.advancement {
+                        if let Some(adv) = &looop.advancement {
                             self.resolve_expr(adv.clone());
                         }
                     }
@@ -59,6 +59,14 @@ impl Interpreter {
                     let result = self.resolve_expr(expr);
                     println!("{}", result);
                 }
+
+                Statement::If(If {condition, body_true, body_false}) => {
+                    if matches!(self.resolve_expr(condition.clone()), Value::I64(0)) {
+                        self.run(body_false.clone());
+                    } else {
+                        self.run(body_true.clone());
+                    }
+                }
             }
 
         }

src/lexer.rs

@@ -16,6 +16,12 @@ pub enum Token {
     /// Print keyword (print)
     Print,
 
+    /// If keyword (if)
+    If,
+
+    /// Else keyword (else)
+    Else,
+
     /// Left Parenthesis ('(')
     LParen,
 
@@ -204,6 +210,8 @@ impl<'a> Lexer<'a> {
                     let token = match ident.as_str() {
                         "loop" => Token::Loop,
                         "print" => Token::Print,
+                        "if" => Token::If,
+                        "else" => Token::Else,
                         _ => Token::Ident(ident),
                     };
 

src/parser.rs

@@ -92,13 +92,24 @@ pub struct Loop {
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]
-pub enum Statement {
-    Expr(Expression),
-    Loop(Loop),
-    Print(Expression),
+pub struct If {
+    /// The condition
+    pub condition: Expression,
+    /// The body that is executed when condition is true
+    pub body_true: Ast,
+    /// The if body that is executed when the condition is false
+    pub body_false: Ast,
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]
+pub enum Statement {
+    Expr(Expression),
+    Loop(Loop),
+    If(If),
+    Print(Expression),
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Default)]
 pub struct Ast {
     pub prog: Vec<Statement>
 }
@@ -124,7 +135,6 @@ impl<T: Iterator<Item = Token>> Parser<T> {
                 }
                 Token::EoF => break,
                 Token::RBraces => {
-                    self.next();
                     break;
                 }
 
@@ -156,6 +166,8 @@ impl<T: Iterator<Item = Token>> Parser<T> {
                 Statement::Print(expr)
             }
 
+            Token::If => Statement::If(self.parse_if()),
+
             // If it is not a loop, try to lex as an expression
             _ => {
                 let stmt = Statement::Expr(self.parse_expr());
@@ -170,11 +182,41 @@ impl<T: Iterator<Item = Token>> Parser<T> {
         }
     }
 
-    // loop i < 1_000; i = i +1 {
-    //     if i % 3 == 0 | i % 5 == 0 {
-    //         sum = sum + i;
-    //     }
-    // }
+    fn parse_if(&mut self) -> If {
+        if !matches!(self.next(), Token::If) {
+            panic!("Error lexing if: Expected if token");
+        }
+
+        let condition = self.parse_expr();
+
+        if !matches!(self.next(), Token::LBraces) {
+            panic!("Error lexing if: Expected '{{'")
+        }
+
+        let body_true = self.parse();
+
+        if !matches!(self.next(), Token::RBraces) {
+            panic!("Error lexing if: Expected '}}'")
+        }
+
+        let mut body_false = Ast::default();
+
+        if matches!(self.peek(), Token::Else) {
+            self.next();
+
+            if !matches!(self.next(), Token::LBraces) {
+                panic!("Error lexing if: Expected '{{'")
+            }
+
+            body_false = self.parse();
+            
+            if !matches!(self.next(), Token::RBraces) {
+                panic!("Error lexing if: Expected '}}'")
+            }
+        }
+
+        If { condition, body_true, body_false }
+    }
 
     fn parse_loop(&mut self) -> Loop {
         if !matches!(self.next(), Token::Loop) {
@@ -204,6 +246,10 @@ impl<T: Iterator<Item = Token>> Parser<T> {
             _ => panic!("Error lexing loop: Expected ';' or '{{'")
         }
 
+        if !matches!(self.next(), Token::RBraces) {
+            panic!("Error lexing loop: Expected '}}'")
+        }
+
         Loop { condition, advancement, body }
 
     }