comparing inputs(not int inputs) returns AttributeError: 'tuple' object has no attribute 'as_string'

[Gfdcvn]

When I run in my lang
variable cart = []

variable item = usrinput()

while item != 1 then
variable cart = cart + item
variable item = intinput()
show(cart)
finish

It outputs

AttributeError: 'tuple' object has no attribute 'as_string'

What do I do?