On 18/08/2012, at 4:28 AM, Dobes Vandermeer wrote:
>
> Parameters are not supposed to behave this way unless you tell them to ...
> this is ridiculous. If you don't think this is a bug, you are insane.
It's known I'm insane :)
It's not a bug. You DID tell them to. The default for parameters is "val".
By using a val parameter you're allowing the compiler to choose
the evaluation strategy. That's the specification. Its not a bug.
I agree it leads to surprises, the question is: how do we fix it
WITHOUT losing optimisation opportunities?
if you need eager evaluation:
proc b(var i:int)() = {
// ^^^^
// i += 1;
println$ "b, i = "+i;
}
proc a() {
var i = 0;
bb := b(i);
i = 10;
bb;
}
a();
// prints b, i = 0
^^^^^^^^^^^^^
Or:
noinline proc b(i:int)() = {
//^^^^^^
// i += 1;
println$ "b, i = "+i;
}
proc a() {
var i = 0;
bb := b(i);
i = 10;
bb;
}
a();
// prints b, i = 0
You should note that inline has semantics precisely because
it controls evaluation strategy.
Unlike C/C++, where evaluation is fixed at eager for function
calls (and lazy almost everywhere else), up to "sequence
points".
You probably know some things in C/C++ aren't specified:
x[i++] = x[i++]
or something like that (its not undefined, just unspecified
which order is used).
In Felix its the same, evaluation strategy of vals/functions
is unspecified (eager or lazy) by default, or explicitly val,
but you can control it as in C -- rewrite you code using
var, noinline, pointers, or some other mechanism that
resolves it.
--
john skaller
skal...@users.sourceforge.net
http://felix-lang.org
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