Document when FnN is inlined

[safareli]

From ffi

exports.runFn3 = function (fn) {
  return function (a) {
    return function (b) {
      return function (c) {
        return fn(a, b, c);
      };
    };
  };
};

main.purs

module Main where

import Prelude
import Data.Function.Uncurried


x :: Fn3 Int Int Int Int -> Int
x f =  runFn3 f 1 2 3

output/Main/index.js

"use strict";
var Data_Function_Uncurried = require("../Data.Function.Uncurried");
var Prelude = require("../Prelude");
var x = function (f) {
    return f(1, 2, 3);
};
module.exports = {
    x: x
};

But just looking at this library I assume output would have been like runFn3(f)(1)(2)(3), but looks like there is some compiler optimization going on.

search for runFn in https://github.com/purescript/purescript/blob/0ebc45779ed21ee16c2fb48a3a2c42544a560512/src/Language/PureScript/CoreImp/Optimizer/Inliner.hs

Would be nice to add a bit of comment about that, note x f = let z = runFn3 f in f 1 2 3 is not optimised.