[racket ursers] Keyword question

[Kevin Forchione]

Hi guys,
Suppose I have something like the following:

(define (f g . args)
(apply g args))

How would I be able to pass keyword arguments to g?

Kevin

[Kevin Forchione]

After racking my brains for the common lisp &allow-other-keys and googling for the scheme/Racket equivalent, stumbling through mzlib/kw and finally a bit of digging through racket procedure documentation I cobbled together an approach that seems to do what I’m after. So I thought I’d share. Here’s an example:

#lang racket


(define (foo #:a (a 0) #:b (b 1) c (d 3) . rst) (list a b c d rst))

(define show
(make-keyword-procedure (λ (kws kw-args f . args) (keyword-apply f kws kw-args args))))

(show foo #:a 10 2 3 4 5 6 7)
=> '(10 1 2 3 (4 5 6 7))

Now apparently any keywords defined for show itself are captured in the kWh and kw-args lists and would need to be filtered out of those lists before tasing them on to f, but that shouldn’t be too difficult.

Kevin

[Tim Meehan]

If it was just passing keyword arguments to your function, you might be able to do it like this:

; https://docs.racket-lang.org/guide/lambda.html

; https://docs.racket-lang.org/reference/procedures.html

(define greet

  (lambda (given #:last surname)

    (string-append "Hello, " given " " surname)))

; 'apply' allows you to specify a keyword argument ...

(define (test f . args)

  (apply f args #:last "Doe"))

(test greet "John") ; => "Hello, John Doe"

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[David Storrs]

There's also keyword-apply:  https://docs.racket-lang.org/reference/procedures.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._keyword-apply%29%29

(define (f x #:y y #:z [z 10])   (list x y z))

> (keyword-apply f '(#:y) '(2) '(1))

'(1 2 10)

> (keyword-apply f '(#:y #:z) '(2 3) '(1))

'(1 2 3)

> (keyword-apply f #:z 7 '(#:y) '(2) '(1))

'(1 2 7)

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[Philip McGrath]

If they do what you want, `curry` and `curryr` support keyword arguments (as of Racket 7.1) and handle lots of cases.

If you do need to use `make-keyword-procedure`, you may want to combine it with `procedure-reduce-keyword-arity-mask`.

-Philip

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