a Proc#curry note from http://www.sitepoint.com/functional-programming-techniques-with-ruby-part-ii/

proc-curry.rb

# http://ruby-doc.org/core-2.0/Proc.html#method-i-curry
#
# curry → a_proc
#
#   Returns a curried proc.
#
# curry(arity) → a_proc
#
#   If the optional arity argument is given, it determines the number of arguments.
#
#     + If a sufficient number of arguments are supplied, it passes the supplied arguments to the original proc and returns the result.
#     + Otherwise(partial function application), returns another curried proc that takes the rest of arguments.
#

# --> version 1

def add(a, b);       a+b; end
def subtract(a, b);  a-b; end
def multiply(a, b);  a*b; end
def divide(a, b);    a/b; end

# --> version 2

def apply_math(fn, a, b)
  a.send(fn, b)
end

apply_math(:+, 1, 2) # => 3

# We have to write out that function name every time?!

# --> version 3, using curring

apply_math = ->(fn, a, b){ a.send(fn, b) }

add      = apply_math.curry.(:+)
subtract = apply_math.curry.(:-)
multiply = apply_math.curry.(:*)
divide   = apply_math.curry.(:/)

add.(1, 2) # => 3

increment = add.curry.(1)
increment.(41) # => 42