Re: [Scheme-reports] Ballot item #113 "directory contents"

[Aubrey Jaffer <agj@x>]

 | Date: Tue, 11 Jan 2011 23:36:05 +0900
 | From: Alex Shinn <alexshinn@x>
 | 
 | On Tue, Jan 11, 2011 at 9:30 PM, pod <pod@x> wrote:
 | ...
 | > Please forgive my interjections but I couldn't help noticing that
 | > the current ballot item #113 "directory contents" seems rather
 | > lacking in detail and does not got far enough in providing
 | > functionality necessary for "a large class of scripts".  The info
 | > paragraph for this items reads:
 | >
 | >    We've decided to add file-exists? and delete-file, essential
 | >    for a large class of scripts, but still have no way to get a
 | >    list of files in a directory. Do we want to provide an
 | >    interface to this?

SLIB has had "file-exists?" and "delete-file" for all supported
implementations since 1993.

Integrated circuit designs can have thousands of files in a directory.
Fetching the complete list of files can take significant time.

Although SCM provides the Posix functions "opendir", "readdir",
"rewinddir", and "closedir", AFAICR I have never used them directly;
"directory-for-each" provides all the directory functionality I have
needed:

 -- Function: directory-for-each proc directory
     PROC must be a procedure taking one argument.
     `Directory-For-Each' applies PROC to the (string) name of each
     file in DIRECTORY.  The dynamic order in which PROC is applied to
     the filenames is unspecified.  The value returned by
     `directory-for-each' is unspecified.

 -- Function: directory-for-each proc directory pred
     Applies PROC only to those filenames for which the procedure PRED
     returns a non-false value.

 -- Function: directory-for-each proc directory match
     Applies PROC only to those filenames for which
     `(filename:match?? MATCH)' would return a non-false value
     (*note Filenames: (slib)Filenames.).

          (require 'directory)
          (directory-for-each print "." "[A-Z]*.scm")
          -|
          "Init.scm"
          "Iedline.scm"
          "Link.scm"
          "Macro.scm"
          "Transcen.scm"
          "Init5e7.scm"                                                       |

Because the name predicate (pred) and match string are applied only to
filenames in the directory, they are insensitive to path separators.

 | One of the rationales in the first ballot pointed out that
 | just adding file-exists? and delete-file was silly.

I have written many SCM scripts.  File paths are typically passed as
command-line arguments.  Nearly all use "file-exists?".  Some use
"delete-file" (mosthly on temporary files).  Only a few use
"directory-for-each".

So no, just adding file-exists? and delete-file is not silly.


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