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A small question: Are the parent constructor arguments also in the
scope of the LET?
I think they should be. If they are, then we can at least express one
of the "inexpressible" examples I listed:
> ;; Conditionally instantiating the parent with different arguments:
> ;; (actually this specific example can be expressed but would
> ;; require the test for (= y 0) to be duplicated):
>
> (define-type rational
> (parent finite-rational)
> (constructor (lambda (x y)
> (if (= y 0)
> (instantiate (parent 1 0))
> (instantiate (parent x y))))))
as follows:
(define-type rational (x y)
(let ((parent-args (if (= y 0)
(cons 1 0)
(cons x y)))))
(parent finite-rational (car parent-args)
(cdr parent-args)))
Cheers
Andre