问题
We can define a new function like this:
(define (car x y) (+ x y))
And use car as an add function. Meanwhile, we lost the built-in function car. Why does Racket allow this? How could we recover the lost built-in function, here is car.
回答1:
Definitions affect the current module only (and, if you export your definition, then any other modules that import your module). You can always import Racket's built-in functions under a different name, if you want to use car in your module for something else. For example:
(require (only-in racket/base (car racket-car)))
Now, you can use racket-car to refer to the built-in car function.
来源：https://stackoverflow.com/questions/23144047/why-we-can-define-a-function-with-the-same-name-of-a-built-in-function-racket