On 8/24/2011 1:58 AM, Roman Perepelitsa wrote:
2011/8/23 Eric Niebler <eric@boostpro.com>
After playing around with functional languages, I've come to envy how easy they make it to curry functions. Call a 2-argument function with 1 argument and you get a function that takes 1 argument. Pass another argument and it evaluates the function. Simple. In contrast, C++ users have to use binders, which are not as nice.
On a lark, I implemented a wrapper that turns any TR1-style function object into a "curryable" function object (attached). Successive function call invocations bind arguments until enough arguments are bound to invoke the wrapped function. With it you can do the following:
curryable<std::plus<int> > p; auto curried = p(1); int i = curried(2); assert(i == 3);
Is there any interest in such a thing?
I think it's a very useful thing to have!
curryable should probably be renamed to curried (this is the term http://en.wikipedia.org/wiki/Currying uses). A generator for curried objects named curry would be a nice addition too, as would be the reverse - uncurry.
Thanks. It's important to get the terminology right. But I thought uncurry had to do with tuples holding arguments.
By the way, don't you need to manually pass arity in the general case? What if the underlying functor is callable with one argument, but also with two?
As soon as enough arguments are collected to make a valid call of the curried function, it gets called. This seems reasonable to me.
I think this is the case with functors generated by bind -- they appear to be callable with any number of arguments.
Ouch. :-( One option, which I don't like, is to "fix" bind to disable any operator() overloads that result in an invalid invocation of the bound function. That can be done easily with the is_callable_with metafunction in my curryable implementation, but would reduce portability somewhat.
FWIW, Egg<http://p-stade.sourceforge.net/egg/doc/html/egg/function_adaptors.html>has curryN (where N is a number literal) and uncurry.
Of course, I'd prefer it if it just worked without needing to be told the arity. That's what I was aiming for. -- Eric Niebler BoostPro Computing http://www.boostpro.com