Re: [PATCH] Make some local functions public (was: Re: lily-library.scm question)

[Mark Polesky]

Neil Puttock wrote:
> -(define (split-at-predicate predicate lst)
> +(define-public (split-at-predicate predicate lst)
>
> Can you amend the docstring for this, since the example given is
> a bit broken (the cons part shouldn't be there):
>
> (split-at-predicate (lambda (x y) (= (- y x) 2)) '(1 3 5 9 11)
> (cons '() '()))"


[PATCHES attached]

Neil, I ended up rewriting the procedure. Can you verify that I
didn't accidentally change some of its original functionality? I'm
pretty sure it's fine, but we like to be thorough, right? At the
moment, the only place I see this used in the source is in
chord-ignatzek-names.scm, line 250.


current version:

(define (split-at-predicate predicate lst)
 "Split LST = (a_1 a_2 ... a_k b_1 ... b_k)
  into L1 = (a_1 ... a_k ) and L2 =(b_1 .. b_k) 
  Such that (PREDICATE a_i a_{i+1}) and not (PREDICATE a_k b_1).
  L1 is copied, L2 not.

  (split-at-predicate (lambda (x y) (= (- y x) 2)) '(1 3 5 9 11) (cons '() 
'()))"
 
 ;; " Emacs is broken

 (define (inner-split predicate lst acc)
   (cond
    ((null? lst) acc)
    ((null? (cdr lst))
     (set-car! acc (cons (car lst) (car acc)))
     acc)
    ((predicate (car lst) (cadr lst))
     (set-car! acc (cons (car lst) (car acc)))
     (inner-split predicate (cdr lst) acc))
    (else
     (set-car! acc (cons (car lst) (car acc)))
     (set-cdr! acc (cdr lst))
     acc)))
 
 (let* ((c (cons '() '())))
   (inner-split predicate lst  c)
   (set-car! c (reverse! (car c)))
   c))

________________________________________________

my version:

(define-public (split-at-predicate predicate lst)
  "Split LST (into 2 lists) at the first element that returns #f for
   (PREDICATE previous_element element), and return the 2 new lists as a
   pair. Example: (split-at-predicate < '(1 2 3 2 1)) ==> ((1 2 3) 2 1)"
  (if (< (length lst) 2)
      (cons lst '())
      (let loop ((L0 (list (car lst))) (L1 (cdr lst)))
        (cond ((null? L1) (cons L0 L1))
              ((predicate (car (last-pair L0))
                          (car L1))
                 (loop (append L0 (list (car L1)))
                       (cdr L1)))
              (else (cons L0 L1))))))

________________________________________________


> - (define (inner-split predicate lst acc)
> + (define-public (inner-split predicate lst acc)
>
> This can't be public, since it's inside split-at-predicate.

Yes, of course... I blame it on poor indentation!


> -(define (number->octal-string x)
> +(define-public (number->octal-string x)
>
> Is this ever likely to be used?

Yes, I need it for my weekly octal game-night!
http://en.wikipedia.org/wiki/Octal_games
My abacus just isn't cutting it anymore.

- Mark

0001-lily-library.scm-Rewrite-split-at-predicate-procedur.patch
Description: Binary data

0002-lily-library.scm-Make-some-local-functions-public.patch
Description: Binary data