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Re: Adding wc to Bournish

From: Ludovic Courtès
Subject: Re: Adding wc to Bournish
Date: Wed, 15 Jun 2016 15:56:43 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Efraim Flashner <address@hidden> skribis:

> From 09eef9cd841a7d212e024be0609168611923696b Mon Sep 17 00:00:00 2001
> From: Efraim Flashner <address@hidden>
> Date: Sun, 22 May 2016 14:56:06 +0300
> Subject: [PATCH] bournish: Add `wc' command.
> * guix/build/bournish.scm (lines+chars, only-files, wc-commands,
> wc-command-implementation, wc-l-command-implementation,
> wc-c-command-implementation): New variables.

s/variables/procedures/ :-)

> (%commands): Add wc command.


> +(define (only-files files)
> +  (filter (lambda (file)
> +            (catch 'system-error
> +              (lambda ()
> +                (stat file))
> +              (lambda args
> +                (let ((errno (system-error-errno args)))
> +                  (format (current-error-port) "~a: ~a~%"
> +                          file (strerror errno))
> +                  #f))))
> +          files))
> +
> +(define (wc-command-implementation . files)
> +  (for-each
> +    (lambda (file)
> +      (let-values (((lines chars)
> +                    (call-with-input-file file lines+chars)))
> +                  (format #t "~a ~a ~a~%" lines chars file)))
> +    ((@@ (guix build bournish) only-files) files)))

I prefer the approach Ricardo suggested, I think it’s more concise and

Also, note that @@ would not be needed here; @@ serves to access private
bindings within a specific module:

Last, do not miss the bit about docstrings at:


With these changes, we’re all set.  Thanks!

>From a GSoC viewpoint, I think we must move to the compilation part
now.  Specifically, I think the next step is to start parsing Bash

For that we could use SILex + parse-lalr, but these are not the nicest
tools for the job.  Better tools would be “parsing expression grammars”
(the (ice-9 peg) module in Guile 2.1) or parser combinators, though I
don’t think there’s a directly usable Guile library for that.  Maybe
Eric or David can comment?

The goal is to have a parser that returns an abstract syntax tree (AST)
as an sexp:

  (parse "(cd /foo; ls $HOME) && echo *.a ; echo done")
         (sequence (command "cd" "/foo")
                   (command "ls" (variable-ref "HOME"))))
       (command "echo" (glob "*.a")))
     (command "echo" "done"))



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