# Stab Operator - Lambdas in Ruby 1.9 or later.
# Y Combinator
# Ruby supports a syntax for lambdas known as the 'stab' operator.
# Rather than something like lambda { a < 5 },
# you can type -> { a < 5 }.
#
# Below is a version of the fibonacci sequence that can
# perform recursive calls without named functions.
#
# Improver function for fibonacci sequence
# Assumes that the 0th element of the sequence is 0,
# and the 1st element of the sequence is 1.
fib_improver = ->(partial) {
->(n) { n < 2 ? n : partial.(n-1) + partial.(n-2) }
}
# The y combinator
y = ->(f) {
->(x) { x.(x) }.(
->(x) { f.(->(v) { x.(x).(v)}) }
)
}
# Using the stab operator and y combinator, we can
# write a fibonacci function with anonymous functions
# This solution is not memoized and so will be very slow.
fib = fib_improver.(y.(fib_improver))
p fib.(1)
p fib.(10)
# Notice that after loading, fib isn't defined anymore.