Postfix

Simple evaluator of a list of values and functions given in postfix order.

{:ok, 10} = Postfix.eval([2, 3, &*/2, 4, &+/2])

Usage

Functions are evaluated with all the operands to their left, and the result replaces the function it's operands in the list and evaluation continues.

If any function returns an {:ok, value} tuple then the value is unwrapped and used as the result.

Any function that fails with an {:error, _} tuple short-circuits and becomes the result of the evaluation,

It is not possible to pass a function to a higher-order function as it will be evaluated.

Given the filter example:

is_odd? = fn x -> rem(x, 2) == 0 end
Enum.filter(1..3, is_odd?)

This cannot be written as:

is_odd? = fn x -> rem(x, 2) == 0 end

{:ok, [2]} = Postfix.eval([1..3, is_odd?, &Enum.filter/2])

However it could be written as:

is_odd? = fn x -> rem(x, 2) == 0 end
filter_odd = fn xs -> Enum.filter(xs, is_odd?) end

{:ok, [2]} = Postfix.eval([1..3, filter_odd])

A stack will be added so results of multiple functions can become inputs to another function.

This package can be installed by adding postfix to your list of dependencies in mix.exs:

def deps do
  [
    {:postfix, "~> 1.0"}
  ]
end