Re: [boost] painless currying

Subject: Re: [boost] painless currying
From: Larry Evans (cppljevans_at_[hidden])
Date: 2011-09-03 10:48:34

On 09/03/11 08:28, Larry Evans wrote:
> On 08/23/11 14:38, Eric Niebler wrote:
>> 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?
> 
> With the 2 attached files (compiled with gcc4.6 and with boost trunk
> [which svn update showed was revision 74198]), the output is:
[snip]
With the revised curryable.cpp, the output is:

/home/evansl/prog_dev/boost-svn/ro/trunk/sandbox-local/build/gcc4_6v/boost-svn/ro/trunk/sandbox/rw/variadic_templates/sandbox/painless_currying/curryable.exe

test<1>:
type_u<0>()
type_u<0,1>(type_u const&)
type_u<0,1>(type_u const&)
type_u<1>()
type_u<1,1>(type_u const&)
type_u<0,1>(type_u const&)
type_u<0,1>(type_u const&)
type_u<1,1>(type_u const&)
type_u<2>()
sout<<type_u<0>
sout<<type_u<1>
sout<<type_u<2>
test<0>:
type_u<0>()
type_u<0,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1>()
type_u<1,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1,0>(type_u const&)
type_u<2>()
type_u<2,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1,0>(type_u const&)
type_u<2,0>(type_u const&)
type_u<3>()
type_u<3,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1,0>(type_u const&)
type_u<2,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1,0>(type_u const&)
type_u<2,0>(type_u const&)
type_u<3,0>(type_u const&)
type_u<4>()
type_u<4,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1,0>(type_u const&)
type_u<2,0>(type_u const&)
type_u<3,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1,0>(type_u const&)
type_u<2,0>(type_u const&)
type_u<3,0>(type_u const&)
type_u<4,0>(type_u const&)
type_u<5>()
type_u<5,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1,0>(type_u const&)
type_u<2,0>(type_u const&)
type_u<3,0>(type_u const&)
type_u<4,0>(type_u const&)
type_u<0,0>(type_u const&)
type_u<1,0>(type_u const&)
type_u<2,0>(type_u const&)
type_u<3,0>(type_u const&)
type_u<4,0>(type_u const&)
type_u<5,0>(type_u const&)

Compilation finished at Sat Sep  3 09:41:23

which reveals that, when passed arguments that cannot
possibly be valid, the arguments just keep accummulating
in the curryable<F,Args...>::argI.  It would be helpful
if some diagnostic were issued in case too many arguments
are supplied.

-regards,
Larry