[racket] redefining primitives?

About a minute ago, Todd O'Bryan wrote:
> Is it possible to redefine primitives, like +, and then provide them
> to another module?

Here's a quick example that provides your two-argument only `+':

  #lang racket
  (require (rename-in racket [+ r+]))
  (provide (except-out (all-from-out racket) r+)
           +)
  (define (+ x y) (r+ x y))

or

  #lang racket
  (provide (except-out (all-from-out racket) +)
           (rename-out [my+ +]))
  (define (my+ x y) (+ x y))

or

  #lang racket
  (provide (except-out (all-from-out racket) +)
           (rename-out [my+ +]))
  (define my+ ; make it have `+' as its printed name
    (let* ([r+ +]
           [+ (lambda (+ x y) (+ x y))])
      +))


> If so, can you also undefine primitives? Like if I wanted to make a
> student language where + only accepted two arguments and the list
> function was unavailable, how could I do that?

Same as above, but add `list' to the `except-out'.

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!