On Monday, December 12th, 2022 at 19:57, Marc Nieper-Wißkirchen <xxxxxx@gmail.com> wrote:

> Amirouche, thank you very much for reading the spec.
>
> I followed your suggestions; please find the hopefully improved draft
> here: https://htmlpreview.github.io/?https://github.com/mnieper/srfi-241/blob/master/srfi-241.html

I think it is better.

I sent a PR against your fork with typofixes.

> Thanks,
>
> Marc
>
> Am Mo., 12. Dez. 2022 um 12:17 Uhr schrieb Amirouche xxxxxx@hyper.dev:
>
> > In SRFI-241, I can read:
> >
> > > Sometimes it is useful to explicitly name the operator in a catamorphism subpattern. Whereas ,[⟨variable⟩ …] recurs to the top of the current match, ,[⟨cata operator⟩ -> ⟨variable⟩ …] recurs to (the result of evaluating) ⟨cata operator⟩. ⟨Cata operator⟩ must evaluate to a procedure that accepts one argument, the matched value, and returns as many values as there are identifiers following the ->.
> >
> > Further down the document describe ⟨cata pattern⟩ as follow:
> >
> > > ,[⟨cata operator⟩ -> ⟨cata variable⟩ …]
> > >
> > > ,[⟨cata variable⟩ …]
> >
> > In the sample implementation, test-match.sps, here is an example use:
> >
> > (define Expr
> > (lambda (env)
> > (lambda (x)
> > (match x
> > ...
> > [(let ([,v ,[e]]) ,[(Expr (cons v env)) -> body])
> > (guard (not (memq 'let env)) (symbol? v))
> > `(let ([,v ,e]) ,body)]
> > ...
> >
> > ref: https://github.com/mnieper/srfi-241/blob/edb8c72d179230435fe87fb15eae2a302f241e41/test-match.sps
> >
> > Compared to ,[⟨cata variable⟩ …] the explicit catamorphism ,[⟨cata operator⟩ -> ⟨cata variable⟩ …] is more general, because it allows to specify the procedure that will be used in the recurrence.
> >
> > Now that I have gone through it carefully, I understand the explicit catamorphism.
> >
> > Maybe my struggle is calling for an example following the paragraph "Sometimes it is useful to explicitly name the operator...".
> >
> > What do you think about introducing the general explicit catamorphism ,(proc -> production) before the shorthand syntax ,(x) ?
> >
> > Maybe it is typo: ⟨cata operators⟩ with an s to operator does not appear in match pattern language.
> >
> > The paragraph starting with "Semantics: A match expression ..." is dense. I wonder whether a bullet point approach will not make reading, and understanding the specification easier.