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Re: meta-comment on typing



Per Bothner scripsit:

> * As a matter of style, I believe type declarations are preferable to
> type-specific arithmetic primitives, especially since Type Declarations
> are Good in themselves.

On reflection, my real objection to hiding type-specific primitives behind
type declarations is that it makes the primitives not first-class: given
that a and b are declared fixnum, only calls that can be recognized as
calls on + are rewritten as calls on fx+.

For example, if the programmer knows that f is a list of fixnums, there
is no way to apply fixnum addition to them, whereas (apply fx+ f) is trivial.
Similarly, a HOF involving fixnums can't take advantage of fixnum arithmetic:

	(define (op f (x :: fixnum) (y :: fixnum)) (f x y))

will perform generic addition, not fixnum addition, if called as (op + 2 3).

If there are worries about namespace pollution, that could be resolved by adding
a procedure IFFIXNUM that maps a generic procedure to its fixnum-specific
alternative:  ((fixnum +) 3 4) is fixnum-specific addition, and so is
(apply (fixnum +) '(3 4)).

-- 
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