Ensure posn also works as pattern in BSL+

[Blaisorblade]

Commit 78ecfc5 didn't alter BSL+ (Beginning Student with List Abbreviations). I tested this change locally on Racket 6.2.1, and the affected code is identical, but please retest before merging.

Failing example in BSL+:

(require 2htdp/abstraction)
(define (f x)
    (match x
      [7 8]
      ["hey" "joe"]
      [(list 1 y 3) y]
      [(cons a (list 5 6)) (add1 a)]
      [(posn 5 5) 42]
      [(posn y y) y]
      [(posn y z) (+ y z)]
      [(cons (posn 1 z) y) z]))

This leads to: match: syntax error in pattern in: (posn 5 5).

[Blaisorblade]

To clarify: this is about valid BSL code failing in BSL+.

[samth]

I think this is ok to merge, but I'm not the expert here. @rfindler @mfelleisen ?

[rfindler]

This looks reasonable to me, but perhaps a test case is in order?

[Blaisorblade]

perhaps a test case is in order?

Good idea. The original commit adds a test for ISL in abstraction-use.rkt; it seems we'd want a section of that file for both BSL and BSL+.
(To avoid misunderstandings: I expect you might be quicker to do this yourself, than to wait for me to figure out Racket's testsuite).

78ecfc5#diff-f29ae2fe358f9044277d9fd49eafdde5

BTW, I'd have wanted to reuse the import from BSL, as for the rest, through all-from beginner:, but wasn't sure how to do that.

[stamourv]

Merged, with test. Thanks!