define-syntax with two-dimensional ellipsis

[ceving]

I have the following macro

(define-syntax define-facts

  (syntax-rules ()

    ((_ (name a0 a1 ...) (v00 v01 ...) (v10 v11 ...) ...)

     '(define (name a0 a1 ...)

        (conde

          ((== a0 v00) (== a1 v01) ...)

          ((== a0 v10) (== a1 v11) ...)

          ...)))))

When I use it with the following data

(define-facts (fathero f c)

  ("Abraham" "Ismael")

  ("Abraham" "Isaac")

  ("Isaac"   "Jacob")

  ("Jacob"   "Benjamin"))

Guile 2.0.9 fulfills my expectation and returns

(define (fathero f c) (conde ((== f "Abraham") (== c "Ismael")) ((== f "Abraham") (== c "Isaac")) ((== f "Isaac") (== c "Jacob")) ((== f "Jacob") (== c "Benjamin"))))

But Chibi 0.7.3 does not carry out the last ellipsis:

(define (fathero f c) (conde ((== f "Abraham") (== c "Ismael")) ((== f "Abraham") (== c "Isaac"))))

Is it a bug?

[ceving]

The macro seems to be a bit controversial.

Gauche fails like Chibi.

Petite Chez succeeds.

Chicken fails with an error.

Gambit fails with an error.

MIT-Scheme succeeds.

Ikarus succeeds.

Scheme48 fails with an error.

[Alex Shinn]

This is illegal according to R7RS 4.3.2:

  Pattern variables that occur in subpatterns followed by one or more

  instances of the identifier ⟨ellipsis⟩ are allowed only in subtemplates

  that are followed by as many instances of ⟨ellipsis⟩.

SRFI 149 proposes to relax this restriction, but Al* Petrofksy
points out that the resulting semantics are not well defined in
http://srfi-email.schemers.org/srfi-149/msg/5375889.  We could
choose and specify the semantics, but I'm not sure there is
a definition that will work intuitively in all cases.

-- 

Alex

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[ceving]

Am Samstag, 11. März 2017 01:46:39 UTC+1 schrieb Alex Shinn:

SRFI 149 proposes to relax this restriction, but Al* Petrofksy
points out that the resulting semantics are not well defined in
http://srfi-email.schemers.org/srfi-149/msg/5375889.  We could
choose and specify the semantics, but I'm not sure there is
a definition that will work intuitively in all cases.

Maybe it is necessary to label the ellipsis to specify which belong together.

(define-syntax foo2
  (syntax-rules ()
    ((foo2 (axis ...) (coordinate ...) :::)
     '(((axis coordinate) ...) :::))))

(foo2 (x y) (1 2) (3 4))
=> (((x 1) (y 2))
    ((x 3) (y 4)))

(define-syntax foo2
  (syntax-rules ()
    ((foo2 (axis :::) (coordinate ...) :::)
     '(((axis coordinate) ...) :::))))

(foo2 (x y) (1 2) (3 4))
=> (((x 1) (x 2))
    ((y 3) (y 4)))