Ruby evaluation strategy

evaluation_strategy.rb

def procedure
  procedure
end

def test_evaluation_strategy(x, y)
  x == 0 ? 0 : y
end

test_evaluation_strategy(0, procedure)

# Explanation
#
# We get `stack level too deep (SystemStackError)` because of applicative-order evaluation strategy. Ruby interpreter at first computes the arguments and only after that passes them into the `test_evaluation_strategy` method. So the call of `0` is just a zero and the `procedure` call gives an infinite recursion.
#
# The other hand, if the Ruby interpreter followed the normal-order evaluation strategy, we would have `0` as the result. That's due to the fact that in the normal-order evaluation interpreter first makes a substitution of the method and its arguments with their expressions and only after that computes the result. Thus after the substitution our method transforms to this:
#
# 0 == 0 ? 0 : procedure
#
# So the result of this expression is `0`.