Re: Adding wc to Bournish

[Efraim Flashner]

On Wed, Jun 15, 2016 at 03:56:43PM +0200, Ludovic Courtès wrote:
> 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
> clearer:
> 
>   https://lists.gnu.org/archive/html/guix-devel/2016-06/msg00525.html
> 
> Also, note that @@ would not be needed here; @@ serves to access private
> bindings within a specific module:
> 
>   https://www.gnu.org/software/guile/manual/html_node/Using-Guile-Modules.html
> 
> Last, do not miss the bit about docstrings at:
> 
>   https://www.gnu.org/software/guix/manual/html_node/Formatting-Code.html
> 
> :-)
> 
> With these changes, we’re all set.  Thanks!

I've attached another patch

> 
> 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
> code.

This part took much longer than I thought it would. Going forward I'll
try to be more pro-active on IRC about asking for help.

> 
> 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?
> 

I get lalr as look-ahead left->right parser and found this¹, but what's SILex?
I also found peg in the master branch of the guile manual².

> 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
>      (success-sequence
>        (subshell
>          (sequence (command "cd" "/foo")
>                    (command "ls" (variable-ref "HOME"))))
>        (command "echo" (glob "*.a")))
>      (command "echo" "done"))
> 
> Thoughts?
> 
> Ludo’.

¹ 
https://www.gnu.org/software/guile/manual/html_node/LALR_00281_0029-Parsing.html#LALR_00281_0029-Parsing
² 
https://www.gnu.org/software/guile/docs/master/guile.html/PEG-Parsing.html#PEG-Parsing

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0001-bournish-Add-wc-command.patch
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