nested functions and #!optional

[Per Bothner]

On 07/26/2012 09:06 AM, Chuah Teong Leong wrote:
> I've got a situation where it unexpectedly throws an exception which puzzled me.
>
> (define (func)
>    (define (nested-func #!optional arg)
>      (set! arg "any string"))
>    (nested-func))
>
> (func)
>
> doing the above throws this
> java.lang.ClassCastException: java.lang.Boolean cannot be casted to
> java.lang.String

This is a bug in type-inference: Kawa infers the type of arg
to be boolean, because the setting of the initial value is the
only assignment it sees.

I seem to remember an existing bug report in Savannah
for a similar bug.

A work-around is add an explicit type specifier:

(define (func)
   (define (nested-func #!optional (arg :: object))
     (set! arg "any string"))
   (nested-func))

Of course I would argue that assigning to a function
parameter is exceedingly poor style!
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/