[plt-scheme] How to execute code in an environment other than it , isdefined?

I forgot to say that your pick-from does not work for:
(pick-from (let ( ) even?) 1 100)
It would if you omit the fenders, but then the first two cases of the macro are 
superfluous.
Jos

----- Original Message ----- 
From: "Kyle Smith" <airfoil at bellsouth.net>
To: <plt-scheme at list.cs.brown.edu>; <grettke at acm.org>; <jos.koot at telefonica.net>
Sent: Sunday, July 15, 2007 10:48 PM
Subject: Re: [plt-scheme] How to execute code in an environment other than it 
,isdefined?


>I just noticed an error in the third clause of pick-form,
> and I went ahead and added the lambda glyph; maybe
> it will show up on the web version correctly:
>
> (module pick-from mzscheme
> (require (lib "42.ss" "srfi"))
> (provide pick-from)
> (define (iter f from to)
> (list-ec (:range x from (add1 to))
> (if (f x))
> x))
> (define-syntax pick-from
> (lambda (stx)
> (syntax-case stx (λ lambda)
> [(_ (λ (var) expr) from to)
> (identifier? #'var)
> (syntax/loc stx
> (iter (lambda (y) ((lambda (var) expr) y)) from to))]
> [(_ (λ (var) expr) to)
> (identifier? #'var)
> (syntax/loc stx
> (iter (lambda (y) ((lambda (var) expr) y)) 1 to))]
> [(_ (lambda (var) expr) from to)
> (identifier? #'var)
> (syntax/loc stx
> (iter (lambda (y) ((lambda (var) expr) y)) from to))]
> [(_ (lambda (var) expr) to)
> (identifier? #'var)
> (syntax/loc stx
> (iter (lambda (y) ((lambda (var) expr) y)) 1 to))]
> [(_ proc from to)
> (identifier? #'proc)
> (syntax/loc stx
> (iter proc from to))]
> [(_ proc to)
> (identifier? #'proc)
> (syntax/loc stx
> (iter proc 1 to))]))))
>
> (require pick-from)
> (pick-from (lambda (a) (zero? (modulo a 3))) 66 99)
> (pick-from (λ (a) (zero? (modulo a 5))) 75 100)
> (pick-from even? 2 20)
> (pick-from odd? 1 17)
> (define triple? (lambda (a) (zero? (modulo a 10))))
> (pick-from triple? 100)
> =========================================
> Welcome to DrScheme, version 370.3-svn9jun2007 [3m].
> Language: SchemeKeys.
> (66 69 72 75 78 81 84 87 90 93 96 99)
> (75 80 85 90 95 100)
> (2 4 6 8 10 12 14 16 18 20)
> (1 3 5 7 9 11 13 15 17)
> (10 20 30 40 50 60 70 80 90 100)
>
> Thats better,
>
> --kyle
>