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Validating a Scheme list

From: Urs Liska
Subject: Validating a Scheme list
Date: Thu, 15 May 2014 10:09:10 +0200
User-agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.0

Hi all,
I am working on a Scheme function and would like to check if I have found the best solution for a specific subpart. Somehow it looks more complicated than necessary.
The function needs to test if each element of a given list is a (sub)list with exactly two elements. So
'((1 2)(3 4))
would return #t while
'((5 6)(7 8 9))
would return #f.
My solution is
\version "2.19.6"
validate =
#(define-scheme-function (parser location lst) (list?)
   (if (memv #f (map (lambda sig
                       (and (list? (car sig))
                            (= 2 (length (car sig))))) lst))
       (display "invalid")
       (display "valid"))

  \validate #'((1 2)(3 4))
  \validate #'((5 6)(7 8 9))
The "framework" doesn't matter, it's just a compilable example. My question is only about the "if" _expression_.

What it does is:
- go through the elements of lst
- produce a list of boolean values,
  - #t if we have a two element list, 
  - #f if not
- check if this intermediate list contains at least one #f

Somehow this looks clumsy to me, and I'd like to know (and learn) if there's a better solution for this.


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