Re: GSOC | Extending Common Lisp support

[Jamison Hope <jrh at theptrgroup dot com>]

On Jun 21, 2012, at 9:21 AM, Charles Turner wrote:

> So what I think we'd want is instead of IsEqv, IsEq's apply2 method
> calling language.booleanType, we'd rather have
> Language.getDefault().booleanType. That's a problem because when the
> primitives.lisp file is being evaluated, we haven't finished setting
> up the Language environment from the common-line parameters. You get
> around this for CL by add the following line to initLisp() (which is
> eventually called from the repl.java setup when it invokes
> Language.getInstance().
>
> Language.setCurrentLanguage(this);
>
> Then we dispatch to the correct booleanType method in Lisp2 and the
> correct answer is obtained for the case example.

I'm a little concerned about the correctness of that change to IsEqv.
With it in place, what happens if you compile this Scheme function and
then invoke it from Common Lisp?

(define (scheme-case)
  (case 'b ((a) 'yes) (else 'no)))

If it works correctly, then fantastic. But my worry is that what will
happen is this:

The Scheme compiler will turn that into something like

Method name:"schemeCase" public static Signature:  
()gnu.mapping.SimpleSymbol
Attribute "Code", length:70, max_stack:3, max_locals:0, code_length:28
  0: getstatic <Field kawa.standard.Scheme.isEqv  
gnu.kawa.functions.IsEqv>
  3: getstatic <'b>
  6: getstatic <'a>
  9: invokevirtual <Method gnu.mapping.Procedure.apply2  
(java.lang.Object,java.lang.Object)java.lang.Object>
 12: getstatic <java.lang.Boolean:FALSE>
 15: if_acmpeq 24
 18: getstatic <'no>
 21: goto 27
 24: getstatic <'yes>
 27: areturn

Then at runtime from CL, Scheme.isEqv.apply2('b, 'a) will return NIL
and the if_acmpeq check for falsehood will be wrong.


Maybe instead have CommonLisp override #'eqv? with its own instance of
IsEqv? That way scheme-case can still call Scheme.isEqv and get #f,
and lisp-case

(defun lisp-case ()
  (case 'b ((a) 'yes) (else 'no)))

can call CommonLisp.isEqv and get NIL.

--
Jamison Hope
The PTR Group
www.theptrgroup.com