[cdr-discuss] Issues with DEFTYPE

[Marco Antoniotti]

On Aug 12, 2008, at 03:48 , Nikodemus Siivola wrote:

...

> DEFSTRUCT also gives you the ability to define what amount to
> mutually
> recursive types:
>
> (defstruct one (two nil :type (or null two)))
> (defstruct two (one nil :type (or null one)))

This mostly works.   However, LW warns you that TWO is not a valid  
type specifier (while compiling a file containing the two  
definitions.  AFAIU, this behavior is "conforming".

>
> All in all, I would be perhaps more interested in a SIMPLE-LIST type,
> (where CAR is always of the same type), then recursive DEFTYPE in
> general:
>
> (deftype int-list ()
>   '(simple-list integer))
>
> In terms of what implmenentations do, what does Allegro do for
>
> (compile nil '(lambda (x) (typep x 'int-list)))

CL-USER> (deftype int-list ()
   '(or null
        (cons integer int-list)))

INT-LIST
CL-USER> (compile nil (lambda (x) (typep x 'int-list)))
#<Function (:ANONYMOUS-LAMBDA 3) @ #x105e6862>
NIL
NIL
CL-USER> (funcall * '(a s d))
NIL
CL-USER> (funcall * '(1 2))
T

>
>
> and
>
> (deftype fixnum-list () '(or null (cons fixnum fixnum-list)))
>
> (compile nil '(lambda (x) (declare (fixnum-list x) (optimize speed))
> (let ((a (first x)) (b (second x))) (when (and a b) (+ a b))))
>
> ? (That is, does it implement recursive types for the compiler as
> well, or do they just work in full calls to TYPEP?)

CL-USER> (deftype fixnum-list () '(or null (cons fixnum fixnum-list)))
FIXNUM-LIST
CL-USER> (compile nil
		  '(lambda (x)
		    (declare (fixnum-list x) (optimize speed))
		    (let ((a (first x)) (b (second x)))
		      (when (and a b) (+ a b)))))
#<Function (:ANONYMOUS-LAMBDA 5) @ #x106d2e7a>
NIL
NIL
CL-USER> (funcall * '( 1 2 ))
3
CL-USER> (funcall * '( 1 a ))

;;; This is the SLIME backtrace

`A' is not of the expected type `NUMBER'
    [Condition of type TYPE-ERROR]

Restarts:
   0: [ABORT-REQUEST] Abort handling SLIME request.
   1: [ABORT] Abort entirely from this (lisp) process.

Backtrace:
   0: (SWANK::DEBUG-IN-EMACS #<TYPE-ERROR @ #x1070970a>)
   1: (SWANK:SWANK-DEBUGGER-HOOK #<TYPE-ERROR @ #x1070970a> #<Function  
SWANK-DEBUGGER-HOOK>)
   2: (ERROR TYPE-ERROR :DATUM A :EXPECTED-TYPE NUMBER :FORMAT-CONTROL  
"~@<`~s' is not of the expected type `~s'~:@>" :FORMAT-ARGUMENTS (A  
NUMBER))
   3: ((:ANONYMOUS-LAMBDA 7) (1 A))
   4: (FUNCALL #<Function (:ANONYMOUS-LAMBDA 7) @ #x1070769a> (1 A))


So it looks like you get a TYPE-ERROR as expected, but I think this is  
coming from the call to +.

Cheers
--
Marco Antoniotti