[phobos] D std.bind

[Jason Spencer]

Andrei Alexandrescu <andrei at ...> writes:

> 
> (Readded Phobos) I wrote a curry in std.functional which I think could 
> be a good starting point.

I'm new to D syntax, but if I read that right, std.curry just gives you an 
alias to a function call of two variables that fills in one for you.  
Deprecating bind would still leave holes for:

- Currying an arbitrary length parameter list
- storing a delegate to the curried function
- composing curries (could be replaced by previous 2 if done in a certain way)
- binding at arbitrary parameter indexes

and maybe a couple of other things.  In short, bind gives support for all 
kinds of partial applications, where as std.curry only allows picking off 
one arg in a two arg function.  If bind were deprecated, is there a plan to
replace the other functionality?

Seems like with the new functional capabilities of D 2, bind is MORE 
necessary, since I would imagine more higher order functions being written 
and extended.  If that's true, then there's gonna be an awful lot of boiler
plate code like:

   auto p_2 = function ReturnType!plus (ParameterTypeTuple!plus[1] arg2,
    ParameterTypeTuple!plus[2] arg3) { return plus(2, arg2, arg3); } ;

rather than

   auto p_2 = bind(plus, 2, _0, _1);

I'd love to see partial applications supported in the language, but short of 
that, I'd say there needs to be some easier way to curry in, say 5 argument 
calls, or else the functional features of D really loose power. Bind already 
provides that.  Maybe it just needs a make-over?

Jason

> Jason Spencer wrote:
> > So is there a recommended way to approach arbitrary depth currying?  
std.algorithm only allows one level. 
> Bind was the only one I knew of that would allow me to "nest" curries as 
deeply as I'd like to.  Other ideas?
> > 
> > Thanks,
> > Jason
> > 
> > 
> > ----- Original Message ----
> >> From: Andrei Alexandrescu <andrei at ...>
> >> To: Jason Spencer <spencer8 at ...>
> >> Cc: Discuss the phobos library for D <phobos at ...>
> >> Sent: Wed, June 16, 2010 2:57:20 PM
> >> Subject: Re: D std.bind
> >>
> >> (Added Phobos.) We haven't tested std.bind in a long time. With the advent 
of 
> >> function literals etc., it seems pointless. Walter and I think it should be 
> >> deprecated.
> > 
> > Andrei
> > 
> > Jason Spencer wrote:
> >> Hi, 
> >> I've 
> >> been trying to get the simplest program that uses bind() to work with D 
2.046 
> >> (or 2.036 or 2.047), but I've run into problem after problem.  First, it 
> >> seems D2 tightened up const handling, and the NullAlias struct of type 
const 
> >> EmptySlot would match is expressions.  After fixing that, I'm now 
> >> getting:
> >>
> >> C:\Jason\D>dmd bTest.d
> >>
> >> C:\tools\dmd2\windows\bin\..\..\src\phobos\std\binder.d(230): Error: alias 
> >> std.bind.Tuple!().Tuple.meta template identifier prependT is not a member 
of 
> >> alias meta
> >> C:\tools\dmd2\windows\bin\..\..\src\phobos\std\binder.d(775): 
> >> Error: no property 'prependT!(T)' for type 'Tuple!()'
> >>
> >> C:\tools\dmd2\windows\bin\..\..\src\phobos\std\binder.d(775): Error: alias 
> >>
> 
std.bind.dynArgTypes!(i,Tuple!(int),Tuple!(DynArg!(0)),1).prependType!(int,DynAr
g!(0)).res 
> >> cannot alias an expression __error
> >>
> >> I'm a D newbie, and the 
> >> syntax is too much for to start on without getting a couple of practice 
programs 
> >> down first.  
> >> Do you know if anyone has tested std.bind in recent 
> >> releases?  I've talked to Tom, but he doesn't seem to be supporting it, 
> >> esp. in D 2.  I've also posted on DigitalMars.D.  Any other 
> >> ideas?
> >>
> >> Thanks,
> >> Jason
>