Using Higher Order Functions in Ruby

Question

I'm trying to learn Ruby right now after learning Python and I'm having trouble translating this code to Ruby:

def compose1(f, g):
    """Return a function h, such that h(x) = f(g(x))."""
    def h(x):
        return f(g(x))
return h

Do I have to translate this using blocks? Or is there a similar syntax in Ruby?

Answer 1

You can do this with lambdas in Ruby (I'm using the 1.9 stabby-lambda here):

compose = ->(f,g) { 
  ->(x){ f.(g.(x)) }  
}

So compose is a function that returns another function, as in your example:

f = ->(x) { x + 1 }
g = ->(x) { x * 3 }

h = compose.(f,g)
h.(5) #=> 16

Note that functional programming is not really Ruby's strong suit - it can be done but it looks a bit messy in my opinion.