atoms vs strings
fjh at cs.mu.oz.au
Tue Apr 29 01:38:46 AEST 1997
Just thought of another use for that `object' module: emulating
:- module atom.
:- type atom.
:- func atom(string) = atom.
:- func atom_name(atom) = string.
:- import_module object.
:- type atom == object(string).
atom(String) = canonical_object(String).
atom_name(Atom) = object_value(Atom).
Nifty, hey? ;-)
The only drawback is that the performance won't be very good. To make
this efficient enough, I think we would have to teach the compiler to
automatically memoize the results of any expensive expression or goal
(i.e. one that involves a procedure call) if it has no input variables --
for that trivial case, memoizing reduces to just checking a boolean
flag. Then an expression like `atom("Hello world")' wouldn't have to
search the table every time it is evaluated.
Prolog compilers do even better: they build the atom table at
link time. We could perhaps do that too, but it doesn't work
very well with dynamic linking.
Fergus Henderson <fjh at cs.mu.oz.au> | "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh> | of excellence is a lethal habit"
PGP: finger fjh at 188.8.131.52 | -- the last words of T. S. Garp.
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