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On 11/15/11 12:47 AM, Niko Matsakis wrote:
>
> On Nov 14, 2011, at 12:53 PM, Brian Anderson wrote:
>
>> std has a 'result::t<T, U>' type that I am trying to use for this
>> purpose. std::io makes use of this now.
>
> Besides exceptions, I do not have a better alternative than
> `std::result`. However, I fear that if we go too far down this
> style, it will very painful and we will find ourselves wishing for
> syntactic sugar to support chaining (whether that is monads or
> something else). At least this has been my experience when working
> in OCaml.
>
> Are we sure that we do not want exceptions?
Actually, since we have `ret`, I'm sure that we can have small
syntactic sugar without resorting to monads.
Assuming we have,
foo(x: str) -> result::t<T, U> { ... }
We could write
let x = #result[foo(y)]
And expand it to
let x = {
let __result = foo(y);
alt(__result) {
ok(z) { z }
err(_){
//Possibly add some logging here
ret __result
}
}
}
In practice, this is already what happens in mozilla-central. Not
ideal, but probably easier to sell to non-fp users as monads, and it
takes advantage of `ret`. I wonder about performance, though. Is there
a way that the compiler could recognize this pattern and somehow
optimize it to attain the same kind of performance as exceptions?
Cheers,
David
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