The easiest way I know is to use `curry`, since Alexis fixed its keyword
argument support
<https://github.com/racket/racket/commit/d1b8ecb3e0edab3ac455486802646b930e88677f>
last year:
#lang racket
(define (fish #:name [name #f]
#:color [color #f]
#:studio [studio #f]
#:eyes [eyes 2])
(~a "The fish " name " is " color ", appears in a movie from " studio "
and has " eyes " eyes."))
(define disney-fish
(curry fish #:studio "Disney"))
(disney-fish #:name "Nemo" #:color "orange")
… but it might be useful to have some other library functions for this sort
of thing: maybe a "curry once" or something like the `adjust-keyword-default
<https://github.com/racket/slideshow/blob/master/slideshow-lib/slideshow/widescreen/base.rkt>`
used in the `#lang slideshow` implementation.
-Philip
On Wed, Jul 10, 2019 at 1:25 PM Jens Axel Søgaard <jensa...@soegaard.net>
wrote:
> Consider the following fishy example wherein we try to
> reuse a function with keyword arguments.
>
>
> (define (fish #:name [name #f]
> #:color [color #f]
> #:studio [studio #f]
> #:eyes [eyes 2])
> (~a "The fish " name " is " color ", appears in a movie from " studio "
> and has " eyes " eyes."))
>
> Let's check see an example:
>
> > (fish #:name "Nemo" #:color "orange" #:studio "Disney")
> "The fish Nemo is orange, appears in a movie from Disney and has 2 eyes."
>
> A few examples later one quickly realizes that Disney has
> a lot of fish in their movies:
>
>
> (fish #:name "Nemo" #:color "orange" #:studio "Disney")
> (fish #:name "Dory" #:color "blue" #:studio "Disney")
> (fish #:name "Marlin" #:color "orange" #:studio "Disney")
> (fish #:name "Wanda" #:color "gold" #:studio "MGM")
> (fish #:name "Blinky" #:color "orange" #:studio "Fox" #:eyes 3)
>
>
> No worries, we can quickly define a disney-fish that simply
> calls fish using the #:studio keyword and passes other keywords
> along. The new disney-fish must accept the same keywords as fish
> (except for the studio one), so procedure-reduce-keyword-arity
> is needed to restrict the accepted keywords.
>
>
> (define disney-fish
> (let ()
> (define (make-disney-fish kws kw-args . rest)
> (keyword-apply/sort fish kws kw-args rest #:studio "Disney"))
>
> (define-values (fish-required fish-allowed) (procedure-keywords fish))
> (define fish-arity (procedure-arity fish)) ; number of by-position
> arguments
>
> (procedure-reduce-keyword-arity
> (make-keyword-procedure make-disney-fish)
> fish-arity
> (remove '#:studio fish-required)
> (remove '#:studio fish-allowed))))
>
> Now we can write:
>
> (disney-fish #:name "Nemo" #:color "orange")
>
> The new disney-fish accepts only keywords accepted by fish,
> so any error reporting works as expected.
>
> But ... the above solution wasn't quick - it took more work than I
> initially expected.
> Am I missing something that makes reusing functions accepting
> keyword arguments easier?
>
> /Jens Axel
>
>
> -- full example --
>
>
> #lang racket
>
> (require kw-utils/keyword-apply-sort)
>
> (define (fish #:name [name #f]
> #:color [color #f]
> #:studio [studio #f]
> #:eyes [eyes 2])
> (~a "The fish " name " is " color ", appears in a movie from " studio "
> and has " eyes " eyes."))
>
> (fish #:name "Nemo" #:color "orange" #:studio "Disney")
> (fish #:name "Dory" #:color "blue" #:studio "Disney")
> (fish #:name "Marlin" #:color "orange" #:studio "Disney")
> (fish #:name "Blinky" #:color "orange" #:studio "Fox" #:eyes 3)
>
> (define disney-fish
> (let ()
> (define (make-disney-fish kws kw-args . rest)
> (keyword-apply/sort fish kws kw-args rest #:studio "Disney"))
> (define-values (fish-required fish-allowed) (procedure-keywords fish))
> (define fish-arity (procedure-arity fish)) ; number of by-position
> arguments
> (procedure-reduce-keyword-arity
> (make-keyword-procedure make-disney-fish)
> fish-arity
> (remove '#:studio fish-required)
> (remove '#:studio fish-allowed))))
>
>
> (disney-fish #:name "Nemo" #:color "orange"
> #:studio "foo")
>
> ; Notes:
> ; > (disney-fish #:name "Nemo" #:color "orange" #:studio "Disney")
> ; correctly shows error (#:studio not expected)
>
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