One of the other comments about continuation passing style seems likely. Basically, all you do is define a function (fun (arg1, arg...) -> result) and invoke i

One of the other comments about continuation passing style seems likely. Basically, all you do is define a function (fun (arg1, arg...) -> result) and invoke it (the exact same way you define a callback with .map(() => result) in Javascript for example). You can store the local state of the function you're currently in, into the callback and state can be passed around that way. (Say you are in a JS function where you defined a number or other variable above: you can use that number in any continuation/closure/function and pass it around, to .map() for example or another function.) I've also heard of recursion as being a way to pass state around in a functional language. If you have a recursive function that takes a num parameter and calls itself with (num + 1), the number can be viewed as mutable state written in a not-so-mutable way.