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macro memoization warning
Someone should have corrected me on an earlier posting: EQ-based macro
expansion memoization doesn't work.
(define-syntax mumble (syntax-rules ()
((mumble var exp)
(list exp (let ((var 13)) exp)))))
(define-syntax grumble (syntax-rules (a)
((grumble a) 5)
((grumble x) 8)))
(let ((a 3))
(mumble a (grumble a))) ;should be (5 8), not (5 5)
Maclisp-style side-effecty memoization works even less well, of
(syntax-rules () ((show x) (list 'x = x))))
(show (let ((y 3)) y)) ;assuming LET is a macro
These problems would be mitigated if macro transformers ensured that
their output was a tree, not a DAG - i.e. no shared substructure.
That is, the two x's in SHOW's output should be copied so as to be
fully non-EQ to each other.