Glenn Linderman wrote:
>
> Nathan, thanks for zeroing in on this paragraph from RFC 23. It raises a
> question in my mind about the meaning of the RFC, and whether the paragraph is
> even necessary, which could answer your question about implementation.
>
> If a curried subroutine is truly generated because of seeing an expression
> containing placeholders, then that expression contains some finite number of
> placeholders. Each placeholder turns into a parameter of the generated
> subroutine. The generated subroutine has, I assume, an internal name or id or
> address by which it is called. However, it can only be called in exactly one
> place: the place in the source code from which the subroutine was generated.
> That place calls it with exactly the correct number of parameters.
>
> Hence, unless there are additional related RFCs not yet submitted which describe
> ways to define names of curried subroutines, and techniques for relating
> curryable expressions such that only one subroutine is generated for multiple
> curried expressions, I fail to see any way in which they can be called with
> fewer than the required number of arguments.
>
> What am I missing?
>
> Nathan Torkington wrote:
just to make sure that i have this right:
currying is effectively a mechanism for partial evaluation of functions. ie add
x y
add3 = add 3
we could then use:
add3 4 == 7
could you not implement currying by simply having some mechanism of storing the
stack? so what happens in the assignment to add3 is that you have a name and a
function associated with this curried function, when it is fully evaluated you
pass all the variables, ie 3 and 4 in this case to add and then it is evaluated.
waiting for the 'your crazy' replies,
peter
> > Perl6 RFC Librarian writes:
> > > =head2 Re-currying deferred expressions
> > >
> > > The subroutines generated by a placeholder are not exactly like the
> > > equivalent subroutines shown above. If they are called with fewer than the
> > > required number of arguments, they return another higher order function,
> > > which now has the specified arguments bound as well.
> >
> > The implementation of this might be far from trivial. The
> > IMPLEMENTATION section of this RFC should address this. How would
> > Perl's innards have to change to make this possible? Dan is, sadly,
> > on holiday. Perhaps another internals hacker could step up and
> > address this.
>
> --
> Glenn
> =====
> There are two kinds of people, those
> who finish what they start, and so
> on... -- Robert Byrne
>
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