[GSLL-devel] Fixing up make-grid-data for clisp (was making copy-to working in clisp+grid: fix to element-type)

[Mirko Vukovic]

This is a follow up on my posted fix to copy-to.  For some reason this has
triggered another
error.  I do not understand how that other error is triggered.  The error
and the fix are discussed
at the bottom of the email

On Fri, Jan 4, 2013 at 10:39 AM, Mirko Vukovic <mirko.vukovic at gmail.com>wrote:

> The following works in sbcl+grid:
>
> (copy-to (make-array 2 :element-type 'double-float :initial-contents
> '(1.0d0 2.0d0)) 'grid:foreign-array)
>
> But it does not work in clisp+grid.
>
> The root cause lies in the function grid/array.lisp/element-type.  It uses
> `(array-element-type grid)'.
>
> But this can present a problem.  Quoting hyperspec:
>
> (Because of *array* <http://26_glo_a.htm#array> *upgrading*, this *type
> specifier* <http://26_glo_t.htm#type_specifier> can in some cases denote
> a *supertype* <http://26_glo_s.htm#supertype> of the *expressed array
> element type* <http://26_glo_e.htm#expressed_array_element_type> of the *
> array*.)
>
> In CLISP, array-element-type returns `T' when passed #(1d0 2d0)
>
> It returns T even when passed a simple array:
>
> (array-element-type (make-array 2 :element-type 'double-float
> :initial-contents
>                       '(1.0d0 2.0d0)
>                       :adjustable nil
>                       :fill-pointer nil
>                       :displaced-to nil) )
>
> The proposed fix is
>
> (defmethod element-type ((grid array))
>   (type-of (row-major-aref grid 0))
>   #+skip(array-element-type grid))
>
> Now copy-to works in clisp as well.
>
> Mirko
>
>
> After finishing this, I recompiled afresh, and got another error that I
traced to make-grid-data and make-array

In clisp, make-array will return an array of NIL's even if the element-type
is specified as double float.  In SBCL make-array
will return an array filled with 1d0.

I had to add some clisp specific code to make-grid-data in order for it to
initialize properly.

First, a helper function:
(defun default-element (element-type)
   "Return a default element depending on element-type
"
   (let ((a-list '((double-float . 1d0)
           (symbol . T))))
     (let ((match (cdr (assoc element-type a-list))))
       (assert match ()
           "Default element type undefined for element-type ~a"
           element-type)
       match)))

And second, a bit of set-up code in make-grid-data.  I broke apart the
(let* statement
to provide an explicit initial element if it has not been specified already:

(defmethod make-grid-data
  ((type (eql 'array)) dimensions rest-spec
   &key (initial-element nil initial-element-p)
   (initial-contents nil initial-contents-p))
  (let ((element-type (top-spec-type rest-spec)))
    #+clisp
    (unless (or initial-element-p
        initial-contents-p)
      (setf initial-element (default-element element-type)
        initial-element-p t))
    (let ((array ... UNCHANGED


Summary:  To fix to copy-to, I modified (defmethod element-type ((grid
array))
For some unknown reason, that triggered an error in the array
initialization routine.
To fix that, I had to add code to make-grid-data, so that it fills
double-float arrays with 0d0
instead of NIL's

I will continue using this code to see if there are additional problems.

BTW, I realize that CLISP is not a preferred platform for speedy
computation, but that is what I use
on Windows, until SBCL gets officially ported to it.  And in addition, it
is a nice cross-check on portability.

Mirko
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