Elm tail call optimization

build.sh

#!/usr/bin/env bash

elm make src/Main.elm --output out.js --optimize

Main.elm

module Main exposing (main)

import Html

sumFromZero : Int -> Int
sumFromZero n =
  sumFromZeroTail 0 n

sumFromZeroTail : Int -> Int -> Int
sumFromZeroTail acc n =
  if n - 0 == 0 -- make sure the equality check is not using structural polymorphic version
  then acc
  else sumFromZeroTail (acc + n) (n - 1)

-- Make sure function is not "treeshaked" away
main = Html.text <| String.fromInt <| sumFromZero 100

out.js

var $author$project$Main$sumFromZero = function (n) {
        // curing optimization
	return A2($author$project$Main$sumFromZeroTail, 0, n);

// currying optimization
var $author$project$Main$sumFromZeroTail = F2(
	function (acc, n) {
		sumFromZeroTail:
		while (true) { // tailcall compiled to loop
			if (!(n - 0)) { // non polymorphic structural equality check
				return acc;
			} else {
				var $temp$acc = acc + n,
					$temp$n = n - 1;
				acc = $temp$acc;
				n = $temp$n;
				continue sumFromZeroTail;
			}
		}
	});