Re: [racket-users] How do I provide a name as both a match expander and contracted function?

[Sorawee Porncharoenwase]

IIUC, this is what Alex Knauth did in
https://github.com/mbutterick/txexpr/pull/8.

On Mon, Dec 30, 2019 at 7:07 PM Jack Firth  wrote:

> If I'm making my own data types, one common thing I want to do is make
> smart constructors that double as match expanders. I could use
> `define-match-expander` with two transformers, but then I can't add a
> contract to the smart constructor with `contract-out`. If I try to write
> this:
>
> (provide
>  (contract-out
>   [foo (->* (widget?) (#:name symbol?) foo?)]))
>
> (define (make-foo widget #:name [name #f])
>   ...)
>
> (define-match-expander foo
>   (syntax-parser [(_ widget) #'(? foo? (app foo-widget widget))])
>   (syntax-parser [(_ arg ...) #'(make-foo arg ...)]))
>
> ...then the use of `contract-out` hides the fact that `foo` is a match
> expander. What should I do?
>
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> 
> .
>

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[racket-users] How do I provide a name as both a match expander and contracted function?

[Jack Firth]

If I'm making my own data types, one common thing I want to do is make 
smart constructors that double as match expanders. I could use 
`define-match-expander` with two transformers, but then I can't add a 
contract to the smart constructor with `contract-out`. If I try to write 
this:

(provide
 (contract-out
  [foo (->* (widget?) (#:name symbol?) foo?)]))

(define (make-foo widget #:name [name #f])
  ...)

(define-match-expander foo
  (syntax-parser [(_ widget) #'(? foo? (app foo-widget widget))])
  (syntax-parser [(_ arg ...) #'(make-foo arg ...)]))

...then the use of `contract-out` hides the fact that `foo` is a match 
expander. What should I do?

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