Mastering Ruby Closures

Currying with Procs

The word “curry” comes from the mathematician Haskell Curry. (I am resisting all attempts to make a lame joke about an Indian dish.) In functional programming, currying is the process of turning a function that takes n arguments into one that takes a single argument, but returns n functions that take one argument.

For example, given a lambda that accepts three parameters:

>> discriminant = lambda { |a, b, c| b**2 - 4*a*c }

>> discriminant.call(5, 6, 7)
=> -104

you could convert it into this:

>> discriminant = lambda { |a| lambda { |b| lambda { |c| b **2 - 4*a*c } } }

>> discriminant.call(5).call(6).call(7)
=> -104

In Ruby, there’s a shorter way to do this using Proc#curry:

>> discriminant = ...