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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:
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- 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