Comments on: Scheme code capsule: currying

By: The Comonad.Reader » Curried Scheme

The Comonad.Reader » Curried Scheme — Sat, 29 Aug 2009 15:45:35 +0000

[...] found a very elegant macro by Piet Delport that handles partial application, but that doesn't deal with the partial application of no arguments or that I'd like to also be [...]

By: The Comonad.Reader » A Robust Currying Macro for Scheme

The Comonad.Reader » A Robust Currying Macro for Scheme — Sat, 29 Aug 2009 15:42:46 +0000

[...] found a very elegant macro by Piet Delport that handles partial application, but that doesn't deal with the partial application of no arguments or that I'd like to also be [...]

By: Auto-Currying vs. Variable-Arity :: I am Richard :: Entries ::

Auto-Currying vs. Variable-Arity :: I am Richard :: Entries :: — Wed, 24 Sep 2008 04:44:53 +0000

[...] anyway for the toy cases like the + function. If your language has macros, then you can do like some people have done and make macros that allow you to auto-curry individual [...]

By: Daniel Martin

Daniel Martin — Wed, 21 Feb 2007 14:18:02 +0000

currying works fine with languages in the ML family because
functions there take a single argument. This “single argument” might, of course, be a tuple. This works transparently to the user because of pattern matching, so that it *looks* like you’re calling a function with multiple arguments.

Not quite. When you make a call that looks like you’re calling a function with multiple arguments in, e.g., Haskell, what’s going on with the idea that a function should take multiple arguments is that the function returns another function. That is:

myFunc 3 4

Is equivalent to the scheme code:

((myFunc 3) 4)

And automatic currying works properly only in the presence of a defined, definite arity. So currying can’t work automatically with arbitrary scheme functions, but the given define-syntax forms let currying work automatically and reasonably efficiently with function definitions that take a fixed number of parameters. With the above definitions, I can still run this:
(repeat 100000
((foo 3) 1 2)
((foo 3 1) 2)
(((foo 3) 1) 2) )
on a rather slow machine (500Mhz K6) in ~7.1 seconds. (under “bigloo -i”)

As Phil shows, manual currying can be done quite easily in scheme, without even a need to get into define-syntax.

By: Chris

Chris — Mon, 05 Feb 2007 20:57:08 +0000

Thanks a lot for your reply Phil. I’m off to learn something new.

By: Phil

Phil — Mon, 05 Feb 2007 20:42:23 +0000

Follow the trail PLT -> Help -> Software: Manuals -> R5RS -> Contents -> 4.1.4 Procedures for a description of the various forms of lambda. Briefly, both curry-args and args collect the function arguments in a list. The curry function takes a function and a list of arguments and returns a new function that saves the original function and the given arguments. The returned function then takes the additional arguments, appends them to the arguments given to the curried function, and applies the original function to the entire list of arguments.

By: Chris

Chris — Mon, 05 Feb 2007 17:32:58 +0000

Phil,
I guess I have been missing something, but your code above strikes me as brilliant. I don’t completely understand it and I very much want to. What is the significance of the dotted pair in the function definition? and lambda’s “arg” not being enclosed in parenthases? Can you point me toward a tutorial or something? I have PLT. Thanks.

By: Phil

Phil — Mon, 05 Feb 2007 14:17:24 +0000

> (define (curry func . curry-args)
(lambda args
(apply func (append curry-args args))))
> ((curry + 1) 2)
3
> ((curry + 1 2) 3)
6
> ((curry + 1 2) 3 4)
10

By: eclig

eclig — Sun, 04 Feb 2007 11:58:57 +0000

currying works fine with languages in the ML family because
functions there take a single argument. This “single argument” might, of course, be a tuple. This works transparently to the user because of pattern matching, so that it *looks* like you’re calling a function with multiple arguments.

Scheme, on the other hand, has functions with multiple arguments and multiple arity. And these don’t match with currying.