Proposed definition of SUBST

[Kent M. Pitman <KMP at MIT-MC>]

    Date: Saturday, 4 September 1982  01:02-EDT
    From: Scott E. Fahlman <Fahlman at Cmu-20c>

    Maybe the right move is to eliminate the :TEST-NOT option for SUBST.
    All you really want here is some sort of equality test, so :TEST-NOT
    makes no real sense here.  Don't we have some precedents for this?...
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Why not just flush all :TEST-NOTs and make a primitive COMPLEMENT as:

(DEFUN COMPLEMENT (FN) #'(LAMBDA (&REST STUFF) (NOT (APPLY FN STUFF))))

a smart compiler could generate fairly good code for this and in some
cases literal translations from things like (COMPLEMENT #'EQ) to #'NEQ could
be done, etc. I suspect the constant argument case will occur very often
so this optimization will be a very productive one. Then people would just
write :TEST (COMPLEMENT #'EQ) if it mattered to them to have the opposite 
test.

T (Yale Scheme) has this. It's much more general than :TEST-NOT (has 
many more uses), simplifies the internal code of many system functions, 
and simplifies the language definition.

-kmp