On Feb 14, 2012, at 12:18 AM, Erik Silkensen wrote: > Another option is you could turn change your fib function to be 'mk-fib' that > returns a new instance of the fib function each time it's called: > > (define (mk-fib) > (let ([n0 -1] [n1 1]) > (lambda () > (let ([next (+ n0 n1)]) > (set! n0 n1) > (set! n1 next)) > n1)))
I frequently assign this sort of thing near the end of a first programming course. First, I have students write a function "next" which returns how many times it's been called. Then "next-color", which on successive calls returns "red", "orange", "yellow", "green", "blue", "violet", #f, #f, ... Then "make-lister", which on input (list "red" "orange" "yellow" "green" "blue" "violet") returns a function acting like "next-color". One suggestion: I would have mk-fib take in two parameters specifying the initial values of fib, rather than always making them -1 and 1. Stephen Bloch sbl...@adelphi.edu
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