Feature #9783: [PATCH] Add Method#curry

• Status: Closed
• Assignee: -
• Target version: -

[plexus (Arne Brasseur)]

There is already Proc#curry, but to curry a method you need to go through to_proc. This patch adds Method#curry which delegates to method.to_proc.curry.

Looking forward to seeing this discussed.

[plexus (Arne Brasseur)]

• File 0001-Implement-Method-curry-which-delegates-to-to_proc.cu.patch 0001-Implement-Method-curry-which-delegates-to-to_proc.cu.patch added

Updated the patch with documentation. There's an interesting side effect to be considered. Method#to_proc returns a lambda that checks its arity. Proc#curry takes an optional arity argument. If this doesn't match the method's arity then the result can not be called.

def two_args(a,b)
end

curried = method(:two_args).to_proc.curry(1)

curried.(1)
#  -:4:in `curry': wrong number of arguments (1 for 2) (ArgumentError)
#  	from -:4:in `<main>'

curried.(1, 2)
#  -:4:in `curry': wrong number of arguments (1 for 2) (ArgumentError)
#  	from -:4:in `<main>'

curried.(1, 2, 3)
#  -:4:in `curry': wrong number of arguments (1 for 2) (ArgumentError)
#  	from -:4:in `<main>'

In the case of a method with variable arguments the arity argument is important though, because otherwise the currying has no effect.

def varargs(*args)
  args
end

curried = method(:varargs).to_proc.curry
curried.(1) # => [1]
curried.(1,2) # => [1, 2]
curried = method(:varargs).to_proc.curry(3)
curried.(1) # => #<Proc:0x007f0cb8fc6fe0 (lambda)>
curried.(1).(2).(3) # => [1, 2, 3]

I think it would make sense for a Method#curry method to raise an error or at least give a warning when passing the wrong arity to a fixed-arity function.

[matz (Yukihiro Matsumoto)]

Looks good to me, except that I don't see any real use-case.
But it's true for Proc#curry itself.

Matz.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

Applied in changeset r46461.

---

proc.c: Implement Method#curry

• proc.c (rb_method_curry): Implement Method#curry, which delegates
  to to_proc.curry. [ruby-core:62212] [Feature #9783]