[mercury-users] unification and polymorphism
pets at students.cs.mu.OZ.AU
Thu Aug 6 10:15:11 AEST 1998
On Wed, 5 Aug 1998, Fergus Henderson wrote:
> I think it would be nice if there was a compiler option that
> if enabled caused the compiler to specialize unifications of
> polymorphic data types if the type was known. The compiler has
> all the necessary information to do this specialization, the
> only reason that it is not done is that no one has implemented
> it yet.
Maybe it would be good to bring back the old `fastcode' and `compactcode'
directives from DEC-10 Prolog. It does seem useful to be able to coach the
compiler about which bits of code are used most. In the context of Mercury,
you could interpret
:- pragma fast_code.
as requesting that any polymorphic goals for which the types are known, up
to the next
:- pragma compact_code.
declaration, should be specialized. If this is being done, I suppose you
might as well specialize any other calls to the same predicates with the
same polymorphic types and in the same mode: as long as you've generated
the code, you might as well make use of it! Anyway, this would give
finer-grain control over the optimization than a switch which would have to
be turned on for a whole module or not at all.
This is going to be hard to implement for intermodule calls, though.
One way to cut down on code bloat: share identical code. E.g., the types
:- type t1 ---> t1(int,int).
:- type t2 == int.
:- type t3 --> t3(t2,t2).
could share their unification and comparison code. Maybe you already do
this? Anyway, they could also share all specialized versions of polymorphic
-Peter Schachte | There's no left or right, just up and down.
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