[rlox] Implement Assignment (for global variables)

rlox/src/bc.rs

@@ -26,6 +26,7 @@ pub enum Op {
 
     DefineGlobal { offset: u8 },
     GetGlobal { offset: u8 },
+    SetGlobal { offset: u8 },
 }
 
 #[derive(Clone, Debug, PartialEq)]

rlox/src/lc.rs

@@ -468,7 +468,14 @@ impl<'src> Parser<'src> {
                 }
                 TokenType::Identifier => {
                     let offset = self.add_string(chunk, token.span);
-                    chunk.add_op(Op::GetGlobal {offset}, token.line);
+
+                    if self.scanner.peek().is_some_and(|t| t.ttype == TokenType::Equal) {
+                        self.scanner.next();
+                        self._expression(chunk, Precedence::Assignment)?;
+                        chunk.add_op(Op::SetGlobal {offset}, token.line);
+                    } else {
+                        chunk.add_op(Op::GetGlobal {offset}, token.line);
+                    };
                 }
                 _ => {
                     return Err(self.error_at(token, ParseErrorKind::IncompleteExpression));
@@ -566,6 +573,7 @@ impl<'src> Parser<'src> {
 
         match self.scanner.peek() {
             Some(token) if token.ttype == TokenType::Equal => {
+                self.scanner.next();
                 self.expression(chunk)?;
             },
             _ => {
@@ -757,6 +765,7 @@ mod tests {
         let mut parser = Parser::new(scanner);
         let mut chunk = Chunk::new();
         parser.compile(&mut chunk);
+
         assert_eq!(parser.errors, vec![]);
         assert!(chunk.instr_eq(expected));
     }
@@ -897,17 +906,35 @@ mod tests {
         test_parse_program(source, &expected);
     }
 
+    #[test]
     fn basic_var_decl_with_initializer() {
         let source = "var x = 1 + 1;";
         use crate::bc::Op::*;
         let x = GC::new_string("x");
         let expected = Chunk::new_with(
             vec![Constant {offset: 1}, Constant {offset: 2}, Add, DefineGlobal { offset: 0 }],
-            vec![],
+            vec![1, 1, 1, 1],
             vec![x.get_object().into(), Value::from(1.0), Value::from(1.0)],
             LinkedList::new(),
         );
 
         test_parse_program(source, &expected);
     }
+
+    #[test]
+    fn assign() {
+        let source = "var x = y = z;";
+        use crate::bc::Op::*;
+        let x = GC::new_string("x");
+        let y = GC::new_string("y");
+        let z = GC::new_string("z");
+        let expected = Chunk::new_with(
+            vec![GetGlobal { offset: 2 }, SetGlobal { offset: 1 }, DefineGlobal { offset: 0 }],
+            vec![1, 1, 1],
+            vec![x.get_object().into(), y.get_object().into(), z.get_object().into()],
+            LinkedList::new(),
+        );
+
+        test_parse_program(source, &expected);
+    }
 }

rlox/src/vm.rs

@@ -1,6 +1,6 @@
 use crate::bc::{Chunk, Op, TraceInfo, Value};
 use crate::gc::{GcHandle, ObjString, ObjectType, GC};
-use std::collections::{HashMap, LinkedList};
+use std::collections::{hash_map, HashMap, LinkedList};
 use std::io;
 use std::rc::Rc;
 
@@ -203,12 +203,35 @@ impl VM {
                         Ok(())
                     } else {
                         Err(
-                        VMError::Runtime(
-                            format!("Undefined variable '{}'.", ident).into(),
-                            self.pc,
-                        ))
+                            VMError::Runtime(
+                                format!("Undefined variable '{}'.", ident).into(),
+                                self.pc,
+                            )
+                        )
                     }?
-                }
+                },
+                Op::SetGlobal { offset } => {
+                    let ident = match chunk.constants[offset as usize] {
+                        Value::Obj(object) => object.downcast::<ObjString>().unwrap(),
+                        _ => todo!(),
+                    };
+
+                    match globals.entry(ident) {
+                        hash_map::Entry::Occupied(mut entry) => {
+                            let v = self.stack.last().unwrap();
+                            entry.insert(v.clone());
+                            Ok(())
+                        },
+                        hash_map::Entry::Vacant(_) => {
+                            Err(
+                                VMError::Runtime(
+                                    format!("Undefined variable '{}'.", ident).into(),
+                                    self.pc,
+                                )
+                            )
+                        },
+                    }?
+                },
             }
         }
 
@@ -303,7 +326,7 @@ mod tests {
     }
 
     #[test]
-    fn read_write_globals() -> Result<(), VMError> {
+    fn define_read_globals() -> Result<(), VMError> {
         let var = GC::new_string("global");
         use Op::*;
         let chunk = Chunk::new_with(
@@ -326,4 +349,32 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn define_write_read_globals() -> Result<(), VMError> {
+        let var = GC::new_string("global");
+        use Op::*;
+        let chunk = Chunk::new_with(
+            vec![
+                Constant { offset: 0 },
+                DefineGlobal { offset: 1 },
+                GetGlobal { offset: 1 },
+                Constant { offset: 2 },
+                Add,
+                SetGlobal { offset: 1 },
+                Pop,
+                GetGlobal { offset: 1 },
+            ],
+            vec![1; 7],
+            vec![Value::from(5.0), Value::from(var.get_object()), Value::from(6.0)],
+            LinkedList::new()
+        );
+
+        let mut vm = VM::new();
+        vm.stdrun(&chunk)?;
+
+        assert_eq!(vm.stack, vec![Value::Number(11.0)]);
+
+        Ok(())
+    }
 }