From: mmc@maruska.dyndns.org (Michal Maruška)
Newsgroups: comp.lang.scheme.scsh
Subject: Re: scsh script --- comment on path handling
Message-ID: <m2u1pdhaz1.fsf@linux11.maruska.tin.it>
Date: 12 May 2002 13:17:06 +0200
-*-scheme-*-
Andrew Tarr <arc@stuff.gen.nz> writes:
> You can find this script at http://arc.stuff.gen.nz/arcfilter.scsh I
> would appreciate any comments or feedback that anyone can give. None
my comment:
this approach is ugly imho:
(define (relativize-to-dir filename dirname)
(let* ((ndirname (file-name-as-directory dirname))
(index (string-length ndirname)))
(if (string= filename ndirname 0 index 0 index)
(string-drop filename index)
(filename))))
Better is to operate on the algebra of paths.
I use this: (find it in http://maruska.dyndns.org/comp/scsh/scheme/fs/tree.scm
and http://maruska.dyndns.org/comp/scsh/scheme/packages.scm)
;; inverse of path-list->file-name:
(define (file-name->path-list filename)
(split-file-name filename))
;; let's have 2 sets, 1 w/ an operation, and 2 mappings
;;
;; get the (inverse) image of op. on:
;; args result
;;trans| ^
;; V proc | inverse
;; ARGS-------> RES
;;
(define (call-in-image proc trans inverse args)
(let ((images (map trans args)))
(inverse
(apply proc images))))
;; fixme: standard ?
(define (nthcdr list n)
(cond ((= n 0) list)
(#t (nthcdr (cdr list) (- n 1)))))
;;; given 2 paths, the difference (not relation !!)
(define (minus path root) ; get the subpath from root -> path
;; only if the start is equal !!
(let ((l (length root))
(lp (length path)))
(if (and (>= lp l)
(list= string= root (take path l)))
(nthcdr path (length root))
(begin
(error "cannot minus" path root)))))
(define (minus* path-string root-string) ; get the subpath from root -> path
(call-in-image
minus
file-name->path-list
path-list->file-name
(list path-string root-string)))
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