def assignment(self) -> Expr.Expr:
'''
Suck up what might be an assignment target, or might be an expression.
'''
possible_lhs = self.logic_or()
'''
If the next token is not "=", we are done, with an expression.
'''
if not self.match(EQUAL):
return possible_lhs
'''
We have "something =" so note the location of the "=" for a possible
later error message; then collect the r-value.
Note the recursion; We take a = b = c as a = (b = c).
'''
error_pos = self.previous()
rhs = self.assignment()
'''
Now ask, We have something =, but is it variable = or property?
'''
if isinstance(possible_lhs, Expr.Variable):
return Expr.Assign(possible_lhs.name, rhs)
if isinstance(possible_lhs, Expr.Get):
return Expr.Set(possible_lhs.object, possible_lhs.name, rhs)
'''
Neither, flag an error at the "=" token noted earlier.
'''
self.error(error_pos, "Invalid target for assignment")
def assignment(self) -> Expr.Expr:
""" Parses an assignment expression """
expr = self.logic_or()
if self.match(TokenType.EQUAL):
equals = self.previous()
value = self.assignment()
if isinstance(expr, Expr.Variable):
return Expr.Assign(expr.name, value)
else:
self.error(equals, "Invalid assignment target")
else:
return expr
def assignment(self) -> Expr.Expr:
expression = self._or()
if self.match(Token.TokenType.EQUAL):
equals = self.previous()
value = self.assignment()
if type(expression) == Expr.Variable:
name = expression.name
return Expr.Assign(name, value)
elif type(expression) == Expr.Get:
get = expression
return Expr.Set(get._object, get.name, value)
else:
self.error(equals, "Invalid assignment target")
return expression
def assignment(self):
'''
slight difference from other recursions because we don't want to have a chain
of "=" operator/operands in the left-hand side. E.g. Can't have expressions
like "a = b + c = d"
The "Control Flow" chapter also includes the starting point for Logical Operators
with "or_op()"
The "Classes" chapter introduces setters which only activate when the Left-Hand
side is a getter that we want to update
'''
expr = self.or_op()
if self.match(TokenType.EQUAL):
equals = self.previous()
value = self.assignment()
if isinstance(expr, Expr.Variable): # aka non-reserved IDENTIFIERS
name = expr.name
return Expr.Assign(name, value)
elif isinstance(expr, Expr.Get):
get = expr
return Expr.Set(get.object, get.name, value)
Lox.Lox.error(equals, "Invalid assignment target.")
return expr
