[mercury-users] Higher order (was The Logic of Mercury)

[Thomas Conway]

On Fri, Sep 10, 1999 at 09:18:22AM EST, Richard A. O'Keefe wrote:
> The important thing in this thread is that stashing a token in a data
> structure instead of stashing a closure doesn't help.  In fact, it can
> make things worse.

OTOH, Lee's proposal is useful in Mercury because the token can quite
happily be given an inst `ground', where as a closure, to be called
must have a `pred(ArgModes) is Determinism' inst which is a subtype
of `ground'. The problem with it is more to do with extensibility and
modules. Consider again the example I showed earlier where the closures
were stored in a "function table". If I have an access predicate for
registering a new function, then any client can add a new function. If
I have to define a type for the `token', then modularity becomes a problem
since Mercury doesn't allow distributed types or predicates.

Thomas
-- 
 Thomas Conway )O+     Every sword has two edges.
     Mercurian            <conway at cs.mu.oz.au>
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