feat: add variable assignments

examples/01_variables.peb

@@ -4,3 +4,7 @@ let var3 = false
 let var4 = var3
 var4 = var2
 var3 = null
+print(var1)
+print(var2)
+print(var3)
+print(var4)

main.py

@@ -13,7 +13,7 @@ def main():
     123
     "This is
      another string" """
-    path: str = "examples/07_math.peb"
+    path: str = "examples/01_variables.peb"
     with open(path, "r") as f:
         source = f.read()
     lexer: Lexer = Lexer()

src/ast/expr.py

@@ -17,6 +17,10 @@ class Expr(ABC):
         ...
 
     class Visitor(ABC, Generic[T]):
+        @abstractmethod
+        def visit_assign_expr(self, expr: AssignExpr) -> T:
+            ...
+
         @abstractmethod
         def visit_binary_expr(self, expr: BinaryExpr) -> T:
             ...
@@ -38,6 +42,15 @@ class Expr(ABC):
             ...
 
 
+@dataclass(frozen=True)
+class AssignExpr(Expr):
+    name: Token
+    value: Expr
+
+    def accept(self, visitor: Expr.Visitor[T]) -> T:
+        return visitor.visit_assign_expr(self)
+
+
 @dataclass(frozen=True)
 class BinaryExpr(Expr):
     left: Expr

src/interpreter/interpreter.py

@@ -1,6 +1,6 @@
 from typing import Any
 
-from src.ast.expr import LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, Expr, VariableExpr
+from src.ast.expr import LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, Expr, VariableExpr, AssignExpr
 from src.ast.stmt import Stmt, PrintStmt, T, ExpressionStmt, LetStmt
 from src.interpreter.error import PebbleRuntimeError
 from src.pebble import Pebble
@@ -21,6 +21,11 @@ class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
             except IndexError:
                 raise PebbleRuntimeError(name, f"Undefined variable '{name.lexeme}'.")
 
+        def assign(self, name: Token, value: Any):
+            if name.lexeme not in self.values:
+                raise PebbleRuntimeError(name, f"Undefined variable '{name.lexeme}'.")
+            self.values[name.lexeme] = value
+
         def clear(self):
             self.values = {}
 
@@ -41,6 +46,11 @@ class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
     def execute(self, stmt: Stmt) -> None:
         stmt.accept(self)
 
+    def visit_assign_expr(self, expr: AssignExpr) -> Any:
+        value: Any = self.evaluate(expr.value)
+        self.env.assign(expr.name, value)
+        return value
+
     def visit_binary_expr(self, expr: BinaryExpr) -> Any:
         left: Any = self.evaluate(expr.left)
         right: Any = self.evaluate(expr.right)

src/parser/parser.py

@@ -1,6 +1,6 @@
 from typing import Optional
 
-from src.ast.expr import Expr, BinaryExpr, UnaryExpr, LiteralExpr, GroupingExpr, VariableExpr
+from src.ast.expr import Expr, BinaryExpr, UnaryExpr, LiteralExpr, GroupingExpr, VariableExpr, AssignExpr
 from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt
 from src.parser.error import ParsingError
 from src.pebble import Pebble
@@ -124,7 +124,18 @@ class Parser:
         return ExpressionStmt(value)
 
     def expression(self) -> Expr:
-        return self.equality()
+        return self.assignment()
+
+    def assignment(self) -> Expr:
+        expr: Expr = self.equality()
+        if self.match(TokenType.EQUAL):
+            equals: Token = self.previous()
+            value: Expr = self.assignment()
+            if isinstance(expr, VariableExpr):
+                name: Token = expr.name
+                return AssignExpr(name, value)
+            self.error(equals, "Invalid assignment target.")
+        return expr
 
     def equality(self) -> Expr:
         expr: Expr = self.comparison()