Re: [boost] painless currying

Subject: Re: [boost] painless currying
From: Eric Niebler (eric_at_[hidden])
Date: 2011-08-25 22:52:47

On 8/25/2011 4:16 PM, Dave Abrahams wrote:
> on Thu Aug 25 2011, Eric Niebler <eric-AT-boostpro.com> wrote:
>> I simply don't see the problem with:
>>
>> f(x) ==> curry
>> f(x, y) or f(x)(y) ==> curry
>> f(x, y, z) or etc. ==> evaluate
>>
>> Can you say specifically what you think the problem is? 
> 
> It just rubs me the wrong way that sometimes passing arguments to a
> function has no execution semantics, but if you happen to complete an
> argument list, suddenly it's called.

OK. You say tomahto.

>> This is how its done in Haskell, for instance (although Haskell
>> doesn't use parens around argument lists).
> 
> Well, no, it's not exactly how it's done in Haskell, because in Haskell
> f is lazy, and that's what makes the difference.
> 
> You probably know this, but I can pass:
> 
>   (f x y z) -- which would be f(x, y, z) in C++
> 
> to another function that will then throw it away, and f will never be
> invoked.
> 
>   let oar x y = if x then x else y
> 
> if I invoke:
> 
>   oar True (f x y z) -- analogous to oar(True,f(x y z)) in C++
> 
> You can prove this to yourself by invoking putStrLn in f.

Yes, I know. I don't consider that difference particularly relevant to
this discussion, though. If (f x y x) type-checks as Int you pass it as
an argument to a function that takes an Int, it type-checks. If you pass
(f x y) as an argument to a function that takes a
unary-function-that-returns-Int, it type-checks.

>>> Yes, it has always been my view that bind was unambiguously better
>>> for non-lazy languages, and at least more flexible even for lazy
>>> ones.
>>
>> Better and more flexible in what ways?
> 
> It's better because it avoids confusion about when things are invoked.

Meh.

> It's more flexible because it allows the 2nd argument to be bound before
> the first argument is available.

You snipped the part of my message where I said that that problem is
easily solvable, and now you're pretending I never said it. :-/

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com