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.