syntax-parse can already perform pattern matching. No need to use match
(define-syntax (multi-compose stx)
(syntax-parse stx
[(_ f:expr g:expr)
#'(compose f g)]
[(_ f:expr funcs:expr ...)
#'(compose f (multi-compose funcs ...))]))
On Wed, Dec 16, 2020 at 1:37 PM unlimitedscolobb <[email protected]>
wrote:
> On Thursday, December 10, 2020 at 6:01:52 PM UTC+1 unlimitedscolobb wrote:
>
>> On Thursday, December 10, 2020 at 5:49:43 PM UTC+1 [email protected]
>> wrote:
>>
>> A macro might be able to generate either of the above from
>>> (comp f g h k)
>>> .
>>>
>> Indeed. I'm re-reading the docs on macros and I think I see a clean and
>> clear way to achieve what I need.
>>
>> I'll post my attempt as soon as I get the time to write it.
>>
>>
> Okay, so this is my shot:
>
> #lang typed/racket
>
> (require (for-syntax syntax/parse racket/match))
>
> (define-syntax (multi-compose stx)
> (syntax-parse stx
> [(_ funcs:expr ...)
> (match-define (list fn fn-1 fs ...)
> (reverse (syntax->list #'(funcs ...))))
> (datum->syntax stx (for/fold ([sexp `(compose ,fn-1 ,fn)])
> ([f (in-list fs)])
> `(compose ,f ,sexp)))]))
>
> (multi-compose f1 f2 ... fn-1 fn) expands to (compose f1 (compose f2 ( ...
> (compose fn-1 fn) ... )))
>
> My syntax-transformation-fu is essentially non-existent, even after
> reading through Greg's Fear of Macros multiple times, so please do tell me
> if you see some flagrant opportunities for improvement in the code above.
>
> I'm planning to throw together a small package with compose-n , compose-3
> to compose-10, and multi-compose, and publish it. It would normally be my
> Christmas package for myself, but it make take some more time :-)
>
> -
> Sergiu
>
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