I think an obvious candidate would be:

(s16-vector-map fx+ a-long-vector-of-shorts another-long-vector-of-shorts)

where you want to eliminate the dispatch overhead of + on a system without type inference.

I've been thinking more and more and I think (contrary to my general preference for conservative, particularizing solutions) that what we need for operations like fx+ is Common Lisp's define-compiler-macro.  This allows the user to declare a syntax keyword for an identifier that already has an ordinary definition.  In keyword position, the macro is used; in any other position, the variable is used.  This basically allows users to write their own compiler optimizations.

After brainstorming with a cow orker, we like the name "define-overloaded-syntax".  I don't think it's necessary to have local versions of this, but I don't object to having them.

Comments?

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