def visit_class_stmt(self, stmt: Class) -> object:
environment = self.env
superclass = None
if stmt.superclass:
superclass = self.evaluate(stmt.superclass)
if not isinstance(superclass, LoxClass):
msg = "Superclass must be a class."
raise PloxRuntimeError(stmt.superclass.name, msg)
environment.define(stmt.name.lexeme, None)
if stmt.superclass:
environment = Environment(environment)
environment.define('super', superclass)
methods = {}
for method in stmt.methods:
is_initializer = method.name.lexeme == 'init'
is_getter = method.getter
function = LoxFunction(method, environment, is_initializer,
is_getter)
methods[method.name.lexeme] = function
klass = LoxClass(stmt.name.lexeme, superclass, methods)
if superclass:
environment = environment.enclosing
environment.assign(stmt.name, klass)
return None
def call(self, interpreter, arguments):
environment = Environment(self.closure)
for (param, val) in zip(self.declaration.params, arguments):
environment.define(param.lexeme, val)
try:
interpreter.execute_block(self.declaration.body.statements,
environment)
except ReturnException as ret:
if not self.initializer:
return ret.value
if self.initializer:
return self.closure.get_at(0, 'this')
def call(self, interpreter, arguments):
environment = Environment(self.closure)
for param, arg in zip(self.declaration.params, arguments):
environment.define(param.lexeme, None)
environment.assign(param, arg)
try:
interpreter._execute_block(self.declaration.body, environment)
except PloxReturnException as return_value:
if self.is_initializer:
return self.closure.get_at(0, 'this')
return return_value.value
if self.is_initializer:
return self.closure.get_at(0, "this")
return None
class Interpreter(Expr.ExprVisitor, Stmt.StmtVisitor):
def __init__(self, error):
self.error = error
self.env = Environment()
self.globals = self.env
self.globals.define('clock', _Clock())
self._locals = {}
def evaluate(self, expr: Expr.Expr):
return expr.accept(self)
def visit_block_stmt(self, stmt: Stmt.Block) -> object:
self._execute_block(stmt.statements, Environment(self.env))
return None
def visit_break_stmt(self, stmt: Stmt.Break) -> object:
raise _PloxBreakException()
def visit_class_stmt(self, stmt: Class) -> object:
environment = self.env
superclass = None
if stmt.superclass:
superclass = self.evaluate(stmt.superclass)
if not isinstance(superclass, LoxClass):
msg = "Superclass must be a class."
raise PloxRuntimeError(stmt.superclass.name, msg)
environment.define(stmt.name.lexeme, None)
if stmt.superclass:
environment = Environment(environment)
environment.define('super', superclass)
methods = {}
for method in stmt.methods:
is_initializer = method.name.lexeme == 'init'
is_getter = method.getter
function = LoxFunction(method, environment, is_initializer,
is_getter)
methods[method.name.lexeme] = function
klass = LoxClass(stmt.name.lexeme, superclass, methods)
if superclass:
environment = environment.enclosing
environment.assign(stmt.name, klass)
return None
def visit_expression_stmt(self, stmt: Stmt.Expression) -> object:
self.evaluate(stmt.expression)
return None
def visit_function_stmt(self, stmt: Stmt.Function) -> object:
if not stmt.anonymous:
function = LoxFunction(stmt, self.env, False)
self.env.define(stmt.name.lexeme, function)
return None
# anonymous function from expression
return LoxFunction(stmt, self.env, False)
def visit_if_stmt(self, stmt: Stmt.If) -> object:
if is_plox_truthy(self.evaluate(stmt.condition)):
self._execute(stmt.then_branch)
elif stmt.else_branch is not None:
self._execute(stmt.else_branch)
return None
def visit_print_stmt(self, stmt: Stmt.Print) -> object:
value = self.evaluate(stmt.expression)
print(stringify(value))
return None
def visit_return_stmt(self, stmt: Stmt.Return) -> object:
value = None
if stmt.value is not None:
value = self.evaluate(stmt.value)
raise PloxReturnException(value)
def visit_var_stmt(self, stmt: Stmt.Var) -> object:
value = None
if stmt.initializer is not None:
value = self.evaluate(stmt.initializer)
self.env.define(stmt.name.lexeme, value)
return None
def visit_while_stmt(self, stmt: Stmt.While) -> object:
while is_plox_truthy(self.evaluate(stmt.condition)):
try:
self._execute(stmt.body)
except _PloxBreakException:
break
return None
def visit_assign_expr(self, expr: Expr.Assign) -> object:
value = self.evaluate(expr.value)
if expr in self._locals:
distance = self._locals[expr]
self.env.assign_at(distance, expr.name, value)
else:
self.globals.assign(expr.name, value)
return value
def visit_ternary_expr(self, expr: Expr.Ternary) -> object:
condition = self.evaluate(expr.condition)
if is_plox_truthy(condition):
return self.evaluate(expr.then_branch)
else:
return self.evaluate(expr.else_branch)
def visit_logical_expr(self, expr: Expr.Logical) -> object:
left = self.evaluate(expr.left)
if expr.operator.type == TokenType.OR:
if is_plox_truthy(left):
return left
else:
if not is_plox_truthy(left):
return left
return self.evaluate(expr.right)
def visit_variable_expr(self, expr: Expr.Variable) -> object:
return self._look_up_variable(expr.name, expr)
def visit_literal_expr(self, expr: Expr.Literal) -> object:
return expr.value
def visit_get_expr(self, expr: Expr.Get) -> object:
obj = self.evaluate(expr.objct)
if isinstance(obj, LoxInstance):
result = obj.get(expr.name)
if isinstance(result, LoxFunction) and result.is_getter:
result = result.call(self, [])
return result
raise PloxRuntimeError(expr.name, "Only instances have properties.")
def visit_grouping_expr(self, expr: Expr.Grouping) -> object:
return self.evaluate(expr.expression)
def visit_set_expr(self, expr: Expr.Set) -> object:
objct = self.evaluate(expr.objct)
if not isinstance(objct, LoxInstance):
raise PloxRuntimeError(expr.name, "Only instances have fields.")
value = self.evaluate(expr.value)
objct.set(expr.name, value)
return value
def visit_subscript_expr(self, expr: Expr.Subscript) -> object:
obj = self.evaluate(expr.objct)
if isinstance(obj, str):
return obj[self.evaluate(expr.index)]
elif isinstance(obj, LoxInstance):
subscript = obj.find_method('__get__')
if subscript:
return subscript.call(self, [self.evaluate(expr.index)])
raise PloxRuntimeError(expr.bracket, "Subscript not supported.")
def visit_super_expr(self, expr: Expr.Super) -> object:
distance = self._locals.get(expr)
superclass = self.env.get_at(distance, "super")
# "this" is always one level nearer than "super"'s environment.
objct = self.env.get_at(distance - 1, "this")
method = superclass.find_method(expr.method.lexeme)
if not method:
msg = f"Undefined property '{expr.method.lexeme}'."
raise PloxRuntimeError(expr.method, msg)
return method.bind(objct)
def visit_this_expr(self, expr: Expr.This) -> object:
return self._look_up_variable(expr.keyword, expr)
def visit_unary_expr(self, expr: Expr.Unary) -> object:
right = self.evaluate(expr.right)
opt = expr.operator.type
if opt == TokenType.MINUS:
check_number_operand(expr.operator, right)
return -right
elif opt == TokenType.BANG:
return is_plox_truthy(right).notify()
return None
def visit_binary_expr(self, expr: Expr.Binary) -> object:
left = self.evaluate(expr.left)
right = self.evaluate(expr.right)
opt = expr.operator.type
if opt == TokenType.PLUS:
if is_plox_number(left) and is_plox_number(right):
return BINARY_OPS[opt](left, right)
if is_plox_string(left) and is_plox_string(right):
return BINARY_OPS[opt](left, right)
if is_plox_string(left) or is_plox_string(right):
return BINARY_OPS[opt](str(left), str(right))
raise PloxTypeError(expr.operator, left, right)
elif opt in EQUALITY_TOKENS:
return BINARY_OPS[opt](left, right)
elif opt in COMPARISON_TOKENS:
if is_plox_number(left) and is_plox_number(right):
return BINARY_OPS[opt](left, right)
if is_plox_string(left) and is_plox_string(right):
return BINARY_OPS[opt](left, right)
raise PloxTypeError(expr.operator, left, right)
elif opt in BINARY_OPS:
check_number_operands(expr.operator, left, right)
if opt == TokenType.SLASH and right == 0:
raise PloxRuntimeError(expr.operator, 'Division by zero.')
return BINARY_OPS[opt](left, right)
return None
def visit_call_expr(self, expr: Expr.Call) -> object:
func = self.evaluate(expr.callee)
arguments = []
for arg in expr.arguments:
arguments.append(self.evaluate(arg))
if not isinstance(func, LoxCallable):
msg = "Can only call functions and classes."
raise PloxRuntimeError(expr.paren, msg)
if len(arguments) != func.arity():
msg = f"Expected {func.arity()} arguments but got {len(arguments)}."
raise PloxRuntimeError(expr.paren, msg)
return func.call(self, arguments)
def _execute(self, stmt):
stmt.accept(self)
def resolve(self, expr: Expr.Expr, depth: int):
self._locals[expr] = depth
def _look_up_variable(self, name: Token, expr: Expr.Expr):
if expr in self._locals:
distance = self._locals[expr]
return self.env.get_at(distance, name.lexeme)
else:
return self.globals.get(name)
def _execute_block(self, statements, environment):
previous = self.env
try:
self.env = environment
for stmt in statements:
self._execute(stmt)
finally:
self.env = previous
def interpret(self, statements):
try:
for statement in statements:
self._execute(statement)
except PloxRuntimeError as e:
self.error(e)
def bind(self, instance):
environment = Environment(self.closure)
environment.define('this', instance)
return LoxFunction(self.declaration, environment, self.initializer)