def return_statement(self):
keyword = self._previous
value = None
if not self._check(TokenType.SEMICOLON):
value = self.expression()
self._consume(TokenType.SEMICOLON, "Expect ';' after return value.")
return Stmt.Return(keyword, value)
def if_statement(self):
self._consume(TokenType.LEFT_PAREN, "Expect '(' after 'if'.")
condition = self.expression()
self._consume(TokenType.RIGHT_PAREN, "Expect ')' after if condition.")
then_branch = self.statement()
else_branch = None
if self._match([TokenType.ELSE]):
else_branch = self.statement()
return Stmt.If(condition, then_branch, else_branch)
def for_statement(self):
self._consume(TokenType.LEFT_PAREN, "Expect '(' after 'for'.")
if self._match([TokenType.SEMICOLON]):
initializer = None
elif self._match([TokenType.VAR]):
initializer = self.var_declaration()
else:
initializer = self.expression()
condition = Expr.Literal(True)
if not self._check(TokenType.SEMICOLON):
condition = self.expression()
self._consume(TokenType.SEMICOLON, "Expect ';' after loop condition.")
incrementor = None
if not self._check(TokenType.RIGHT_PAREN):
incrementor = self.expression()
self._consume(TokenType.RIGHT_PAREN, "Expect ') after for clauses.")
body = self.statement()
# Lox Code - `for (var a = 0; a < 3; a = a + 1) print a;`
# is ~transalated~ desugared into:
# { // This additional Block limits the scope
# var a = 0;
# while (a < 3){
# print a;
# a = a + 1;
# }
# }
if incrementor != None:
body = Stmt.Block([body, incrementor])
body = Stmt.While(condition, body)
if initializer != None:
body = Stmt.Block([initializer, body])
return body
def statement(self):
if self._match([TokenType.FOR]):
return self.for_statement()
if self._match([TokenType.IF]):
return self.if_statement()
if self._match([TokenType.PRINT]):
return self.print_statement()
if self._match([TokenType.RETURN]):
return self.return_statement()
if self._match([TokenType.WHILE]):
return self.while_statement()
if self._match([TokenType.LEFT_BRACE]):
return Stmt.Block(self.block())
return self.expression_statement()
def function_declaration(self, kind):
'''We reuse this method for both function and method declaration.
`kind` is used to distinguish between the two.
'''
name = self._consume(TokenType.IDENTIFIER, f"Expect {kind} name.")
self._consume(TokenType.LEFT_PAREN, f"Expect '(' after {kind} name.")
parameters = []
if not self._check(TokenType.RIGHT_PAREN):
parameters.append(
self._consume(TokenType.IDENTIFIER, "Expect parameter name."))
while self._match([TokenType.COMMA]):
parameters.append(
self._consume(TokenType.IDENTIFIER,
"Expect parameter name."))
if len(parameters) > 255:
self._error(self._peek(), "Cannot have more than 255 parameters.")
self._consume(TokenType.RIGHT_PAREN, "Expect ')'after parameters.")
self._consume(TokenType.LEFT_BRACE,
"Expect '{' before" + kind + "body.")
body = self.block()
return Stmt.Function(name, parameters, body)
def var_declaration(self):
name = self._consume(TokenType.IDENTIFIER, "Expect variable name.")
value = self.expression() if self._match([TokenType.EQUAL]) else None
self._consume(TokenType.SEMICOLON,
"Expect ';' after variable declaration.")
return Stmt.Var(name, value)
def expression_statement(self):
expression = self.expression()
self._consume(TokenType.SEMICOLON, "Expected ';' after expression.")
return Stmt.Expression(expression)
def print_statement(self):
value = self.expression()
self._consume(TokenType.SEMICOLON, "Expected ';' after expression.")
return Stmt.Print(value)
def while_statement(self):
self._consume(TokenType.LEFT_PAREN, "Expect ')' after while.")
condition = self.expression()
self._consume(TokenType.RIGHT_PAREN, "Expect ')' after condition.")
body = self.statement()
return Stmt.While(condition, body)