destructuring binding at lambda formal

[nyuichi]

(define f (lambda ((a . b)) (+ a b)))

(f (cons 1 2)) ;=> 3

; because let expands to a lambda form, you will be able to do destructuring bind in let forms.
(let (((a . b) (cons 1 2)))
  (+ a b))

[KeenS]

FYI there is a pattern matching library https://github.com/SaitoAtsushi/pattern-match-lambda.
I tried to run test with picrin but an error prevented me.

[nyuichi]

@KeenS

What kind of error did you get?

[KeenS]

@wasabiz below.
macroexpand error while application: macroexpand error while definition: macroexpand error while application: pair required

The cause is this code.

  (define-syntax %if-match-vector
    (syntax-rules ()
      ((_ (literals ...) #() ind e seq alt) seq)
      ((_ (literals ...) #(p r ...) ind e seq alt)
       (%if-match (literals ...) p (vector-ref e ind)
                  (let ((i ind))
                    (%if-match-vector (literals ...) #(r ...) (+ i 1) e seq alt))
                  alt))))

Detailed (debug) log is too long to paste even onto gist.

[zeptometer]

@KeenS This error seems caused when expanding rules including vector. And I think this bug is fixed by #186. Can you test with this fix? (I made branch 'fix-syntax-rules' at this repository)

[KeenS]

@zeptometer It seems not to be fixed. I got this error
macroexpand error while application: pic_get_args: expected vector, but got (0).
The cause is

(define fact
  (pattern-match-lambda ()
                        ((0) 1)
                        ((n) (* n (fact (- n 1))))))

Too specialized to vector?

[nyuichi]

In (picrin experimental lambda) library, there exists what this issue proposed.