David Sletten
2/2/2005 9:50:00 AM
E S wrote:
>
>
> Oh, I was serious. Partial function application (also referred to as
> 'macro binding' and 'currying') means that given a certain function
> (or method), e.g.
>
> def fun(x, y, z)
> q = x + y + z
> end
>
> If this function is invoked with a partial argument list, e.g.
>
> fun 1, 2
>
> Then, instead of throwing some sort of an error, the call would
> produce a new function where the given arguments are bound.
> Essentially, the previous call would yield:
>
> def fun(z)
> q = 1 + 2 + z
> end
>
> So these calls would be equal:
>
> fun(1, 2, 3) # => 6
> ((fun 1, 2) 3) # => 6
> fun(1, 2)(3) # => 6
> x = fun(1, 2); x(3) # => 6
>
> The only problem would be handling the destructive updates, i.e. what
> would happen if one tried to curry this with x:
>
> def fun(x, y, z)
> x = x + y + z
> end
>
> x can't be directly substituted since it's assigned to. It'd have to
> be translated to 'xx = x + y + z' or something.
>
> This probably isn't something most Rubyists, at least initially, would
> be excited about but it's quite useful. I think it'd be possible to
> implement as a library but it'd obviously be fairly slow. Of course
> there's always Haskell :)
>
This isn't exactly what you were asking for, but it fills some of the
gap. It's a fairly straightforward (i.e., ripped off from) translation
of an example by Paul Graham in _ANSI_Common_Lisp_ (pg. 110). He was
attempting to simulate a similar feature from Dylan.
def curry(f, *args)
lambda {|*args2| f.call(*(args + args2))}
end
fun = lambda {|x, y, z| x + y + z}
fun.call(1, 2, 3) => 6
f1 = curry(fun, 1)
f1.call(2, 3) => 6
f2 = curry(fun, 1, 2)
f2.call(3) => 6
I'm fairly new to Ruby, but I think this is the right way to do this.
David Sletten