tags 37086 + notabug
close 37086
thanks
Hi Matthew,
Matthew Henry <mcthe...@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
