in light of recent bugs and discussion I'm thinking about changing
the default evaluation strategy for *procedure* arguments to eager.
This may make procedures less efficient.
If the argument accesses something the procedure modifies,
the semantics may be indeterminate. The problem is that "in principle"
the client doesn't know what the procedure modifies when, or when
the argument is evaluated (or how many times .. :)
This can't happen with functions because functions don't modify things.
In principle generators should be treated the same.
Note this doesn't solve all the problems for example
passing a single pointer value in two arguments,
the procedure can read one and write the other,
in some indeterminate order. Felix doesn't have "restrict"
like C does (and its a dubious idea anyhow because it doesn't
apply to pointers *nested* in other data structures).
Note that the client could fix this by simply passing a var,
eg instead of
p expr;
write
var x = expr;
p x;
or just
p (var expr);
So it isn't clear the change should be made.
--
john skaller
skal...@users.sourceforge.net
http://felix-lang.org
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