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From: Tamas K Papp on 18 May 2010 06:04
Is there a standard way to test if two types are equal?

For example, in ECL,

> (upgraded-array-element-type '(signed-byte 64))
SI:INTEGER64

but it turns out that the two are just synonyms. Currently, I am
testing for that using

(defun type= (type1 type2)
"Test if two types are equal (ie subtypes of each other)."
(and (subtypep type1 type2)
(subtypep type2 type1)))

> (type= 'SI:INTEGER64 '(signed-byte 64))
T
T

but I am wondering if there is something in the HS I missed.

Thanks,

Tamas
From: Frode V. Fjeld on 18 May 2010 06:08
Tamas K Papp <tkpapp(a)gmail.com> writes:

> (defun type= (type1 type2)
> "Test if two types are equal (ie subtypes of each other)."
> (and (subtypep type1 type2)
> (subtypep type2 type1)))

> but I am wondering if there is something in the HS I missed.

No, I believe your TYPE= is the standard trick for this.

--
Frode V. Fjeld

From: Thomas F. Burdick on 19 May 2010 04:02
On May 18, 12:04 pm, Tamas K Papp <tkp...(a)gmail.com> wrote:
> Is there a standard way to test if two types are equal?
>
> For example, in ECL,
>
> > (upgraded-array-element-type '(signed-byte 64))
>
> SI:INTEGER64
>
> but it turns out that the two are just synonyms.  Currently, I am
> testing for that using
>
> (defun type= (type1 type2)
>   "Test if two types are equal (ie subtypes of each other)."
>   (and (subtypep type1 type2)
>        (subtypep type2 type1)))

(defun type= (type1 type2)
(multiple-value-bind (sub1? oops1) (subtypep type1 type2)
(multiple-value-bind (sub2? oops2) (subtypep type2 type1)
(cond
((or oops1 oops2)
(error "No idea if (TYPE= ~S ~S), it certainly sucks that
this is allowed."
type1 type2))
((and sub1? sub2?) t)
(t nil)))))
From: Norbert_Paul on 19 May 2010 05:17
Thomas F. Burdick wrote:
> (defun type= (type1 type2)
> (multiple-value-bind (sub1? oops1) (subtypep type1 type2)
> (multiple-value-bind (sub2? oops2) (subtypep type2 type1)
> (cond
> ((or oops1 oops2)
> (error "No idea if (TYPE= ~S ~S), it certainly sucks that
> this is allowed."
> type1 type2))
> ((and sub1? sub2?) t)
> (t nil)))))

If that sucks you could mimic it:

(defun type= (type1 type2)
(multiple-value-bind (sub1? oops1) (subtypep type1 type2)
(multiple-value-bind (sub2? oops2) (subtypep type2 type1)
(cond ((and sub1? sub2?) (values T T)) ; definitely yes
((and oops1 oops2) (values nil T)) ; definitely no
( T (values nil nil)))))) ; maybe - maybe not

AFAIK there are good reasons for the secondary value.

Norbert
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