recursion schemes

[Raoul Schorer]

Hi,

I recently became interested in recursion schemes, and I noticed that almost all implementations are in typed languages. I understand the advantage of having an implementation using recursion at the type level, but why is it that there are so few material in untyped languages?

For instance, would a recursion schemes racket lib be useful or is there something I am missing? I noticed that there is no such lib, currently.

Thanks,

Raoul

[江泽民]

Actully racket pattern matching syntax has already supported recursion scheme(catamorphism):

(define (eval-expr e)
  (match e
    [`(+ ,(app eval-expr e0) ,(app eval-expr e1))
     (+ e0 e1)]
    [`(- ,(app eval-expr e0) ,(app eval-expr e1))
     (- e0 e1)]
    [(? number?) e]
    ))

在 2019年7月15日星期一 UTC+8上午11:21:14，Raoul Schorer写道：