On Tue, 20 Sep 2005, Andre van Tonder wrote:

> In the following examples, both the formals and the parent arguments can
> easily be factored out to reproduce the surface syntax of the SRFI, with a
> certain loss of expressiveness.

Let me also point out some more problems (sorry ;-):

Factoring out the formals causing loss of expressivity:
-------------------------------------------------------

- We cannot use CASE-LAMBDA for variable arity constructors.
- We cannot express (speudocode):

     (define-type generated-id
       (fields symbol)
       (constructor (let ((count 0))
                      (lambda ()
                        (set! count (+ count 1))
                        (string->symbol ................)))))

Factoring out parent arguments causing loss of expressivity:
------------------------------------------------------------

- We cannot call the parent with different arguments depending
   on the child arguments, e.g.

    (define-type eq-hash-table
      (parent hash-table)
      (constructor (lambda (size hasher)
                     (if (< size 7)
                         (instantiate (eq? (lambda (key) 0) 1))
                                               ; parent arguments
                         (instantiate (eq? hasher size))))))

> In the following examples, INSTANTIATE is a local lexical macro valid in the
> constructor clause that does two orthogonal things:

By the way, since INSTANTIATE would be a lexical macro, this makes it
impossible to write a global procedure that could be reused for more than one
record type.  A positional interface would be superior in this regard.

Cheers
Andre