[racket] [plt-scheme] [redex] matching question

On Fri, Jun 4, 2010 at 1:48 PM, Casey Klein
<clklein at eecs.northwestern.edu> wrote:
> On Fri, Jun 4, 2010 at 1:14 PM, Eric Tanter <etanter at dcc.uchile.cl> wrote:
>> Hi,
>>
>> I have a subtype? metafunction where one clause is as follows:
>>
>> ((subtype? C_0 C_1 CT)
>>   #t
>>   (side-condition (not (equal? (term C_0) (term Object))))
>>   (where (C_0 C_2 any_1 any_2) (class-lookup C_0 CT))
>>   (side-condition (not (equal? (term C_0) (term C_1))))
>>   (side-condition (equal? (term C_2) (term C_1))))
>>
>> ie. C_0 is subtype of C_1 if C_0 directly inherits from C_1
>>
>> I find it redundant that I have to write the above, ie. introducing C_2 in the where clause to then check that C_2 and C_1 are equal.
>>
>> At first I wrote:
>>
>> ((subtype? C_0 C_1 CT)
>>   #t
>>   (side-condition (not (equal? (term C_0) (term Object))))
>>   (where (C_0 C_1 any_1 any_2) (class-lookup C_0 CT))
>>   (side-condition (not (equal? (term C_0) (term C_1)))))
>>
>> putting C_1 directly in the pattern of the where clause, but it did not work (that is to say, it always matched, even if the superclass was different from C_1).
>>
>> Can someone explain me why this is so?
>>
>
> John requested the same behavior a few months ago, and I agree it
> would be very handy.  I'll try to implement it in the next few weeks.
>

This change is in git now. Here's an example.

(define-metafunction STLC
  [(⊢ (e_1 e_2) Γ)
   τ_2
   (where (τ_1 → τ_2) (⊢ e_1 Γ))
   (where τ_1 (⊢ e_2 Γ))]
  [(⊢ x_i ((x_0 τ_0) ... (x_i τ_i) (x_i+1 τ_i+1) ...))
   τ_i]
  [(⊢ (λ (x : τ) e) ((x_0 τ_0) ...))
   (τ → τ_*)
   (where τ_* (⊢ e ((x τ) (x_0 τ_0) ...)))]
  [(⊢ number Γ) Number]
  [(⊢ e Γ) no-type])

(define-language STLC
  (e (λ (x : τ) e)
     (e e)
     x
     number)
  (τ Number
     (τ → τ))
  (x variable-not-otherwise-mentioned)
  (Γ ((x τ) ...)))