Stack overflow today led me to something … very strange. I feel like I must be 
missing something crushingly obvious.

To reproduce: start racket at the command line or hit “run” on a definitions 
window containing only “#lang racket”.

Then, paste:

(define map (lambda (l f)
        ((null? l) '())
        (else (cons (f (car l)) (map (cdr l) f)))

(Note that this version of map takes the function last.) Then, paste:

(map '(3 4 5) add1)

See this error:

map: contract violation
  expected: procedure?
  given: '(4 5)
  argument position: 1st
  other arguments…:

Note that the error occurs on the recursive call. This means that despite being 
inside of a binding of the name map, the function is using the built-in 

When I try doing the same thing with a value defined in the empty program (with 
the name’f’), I see the error 

define-values: assignment disallowed;
 cannot re-define a constant
  constant: f

Which leads me to the suspicion that maybe possibly this message is supposed to 
be shown for the re-definition of ‘map’, as well?

Very confused,


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