GNU bug report logs - #37086
Guile Ice-9 Readline with-readline-completion-function

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From: Matthew Henry <mcthenry <at> gmail.com>
To: Mark H Weaver <mhw <at> netris.org>
Cc: 37086 <at> debbugs.gnu.org
Subject: bug#37086: Guile Ice-9 Readline with-readline-completion-function
Date: Tue, 20 Aug 2019 07:35:21 -0400

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Ah gotcha.  Thanks!

On Mon, Aug 19, 2019 at 11:01 PM Mark H Weaver <mhw <at> netris.org> wrote:

> tags 37086 + notabug
> close 37086
> thanks
>
> Hi Matthew,
>
> Matthew Henry <mcthenry <at> gmail.com> writes:
>
> > Seen in: guile (GNU Guile) 2.2.4
> >
> > When using the with-readline-completion-function, the passed readline
> > uses the default (apropos) completion function instead of the one
> > provided to with-readline-completion-function.
> >
> > I believe that this is because root/guile-readline/ice-9/readline.scm
> > has defined with-readline-completion-function as a function instead of
> > as a macro.  The readline provided in thunk is executed before the
> > body of with-readline-completion-function executes and overrides
> > *readline-completion-function*.
> >
> > As an aside, I think the API would be better if the completion
> > function could be provided to readline directly.
> >
> > Attached is a sample program.
> >
> > Below is sample output of a run of the attached program.  You can see
> > that it's autocompleting Guile functions and variables (the default
> > apropos completion) rather than the provided one which should have had
> > only 3 options with just one starting in "th".
> >
> > ;;;;;;;;;;;;;;;;;;;;;;;;;;;
> > Prompt:
> > Display all 1859 possibilities? (y or n)
> > Prompt: th
> > the-eof-object   the-scm-module   thread-exited?   thunk?
> > the-root-module  thread?          throw
> > Prompt: th
> >
> > (use-modules (ice-9 readline))
> >
> > (with-readline-completion-function
> >  (make-completion-function '("one" "two" "three"))
> >  (readline "Prompt: "))
>
> The problem is that 'with-readline-completion-function' expects a
> "thunk" as the second argument.  A "thunk" is a procedure that takes no
> arguments.  Typically this means that you wrap the relevant code within
> (lambda () ...), like this:
>
>   (use-modules (ice-9 readline))
>
>   (with-readline-completion-function
>    (make-completion-function '("one" "two" "three"))
>    (lambda () (readline "Prompt: ")))
>
> > I'm early in my Scheme journey, but here's a suggested fix:
> >
> > (define-syntax-rule (with-readline-completion-function completer expr
> ...)
> >   "With @var{completer} as readline completion function, call @var{expr
> ...}."
> >   (let ((old-completer *readline-completion-function*))
> >     (dynamic-wind
> >       (lambda ()
> >     (set! *readline-completion-function* completer))
> >       (lambda () expr ...)
> >       (lambda ()
> >     (set! *readline-completion-function* old-completer)))))
> >
> > (export with-readline-completion-function)
>
> This is fine, but it's a different API.  It's true that you need to use
> a macro if you want to avoid wrapping the body within (lambda () ...),
> but just like 'dynamic-wind' itself, 'with-readline-completion-function'
> was designed to be an ordinary procedure that accepts the body
> expression(s) as a THUNK.
>
>    Happy hacking!
>         Mark
>

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