Functional Ruby

Installing

gem install fn-ruby

require 'functional-ruby'

There are some utils for working in ruby in functional style.

Currying, first parameters (apply_head, >>, %)

pow = -> x, y { x ** y }
(pow % 2)[3] #=> 8

Currying, last parameters (apply_tail, <<)

pow = -> x, y { x ** y }
(pow << 2)[3] #=> 9

Composing (compose, *)

f = -> x { x * x }
g = -> x { x + 1 }
(f * g)[3] #=> 16

Mapping (map, |)

f = -> x { x * x }
d = [1, 2, 3]
f | d #=> [1, 4, 9]

Reducing (reduce, <=)

f = -> a, e { a * e }
d = [1, 2, 3]
f <= d #=> 6

Memoization (memoize, +@)

You can make your function memoized just by typing + before it.

fact = +-> n { n < 2 ? 1 : n * fact[n - 1] }
t = Time.now; fact[1000]; Time.now - t #=> 0.018036605
t = Time.now; fact[1000]; Time.now - t #=> 2.6761e-05

Arithmetic

You can use usual arithmetic operators.

+

f = -> x { x * x }
g = -> x { x + 1 }
(f + g)[3] #=> 13

-

f = -> x { x * x }
g = -> x { x + 1 }
(f - g)[3] #=> 5

/

f = -> x { x * x }
g = -> x { x + 1 }
(f / g)[3] #=> 2

mult

The * method is used for composing so we provide symbolic name for this.

f = -> x { x * x }
g = -> x { x + 1 }
f.mult(g)[5] #=> 36

Working with methods

The Symbol#@+ method is overloaded.

def sqr(x)
  x * x
end

def inc(x)
  x + 1
end

(+:sqr * +:inc)[3] #=> 16

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