Question

As an exercise I am trying to define a rule match-rewriter that behaves the same as match-lambda but returns its argument if no match is found. So far I have this:

(define-syntax match-rewriter
  (syntax-rules ()
    ((_ (patt body) ...)
      (λ (x) (match x (patt body) ...)))))

which seems to work perfectly if a match is found.

But, I can’t figure out how to return the argument x if no match is found.

I know that match will throw an exception if no match is found. But I can’t figure out how to catch it and I would like a simpler solution if one exists.

Answer 1

If this question is about the Racket‘s match, then just add a clause that matches anything:

(match x [patt body] ... [_ x])