Defunctionalized Javascript Factorial

fac.kep

var fac = let
    facImpl = \n, sum ->
        (n ? ['fac', n - 1, n * sum] : ['done', sum]),
        
    trampoline = \k -> {
        while (true) {
             switch (k[0]) {
             case 'done': return k[1];
             case 'fac': k = facImpl(k[1], k[2]); break
             }
        }
    }
in
    \n -> trampoline(facImpl(n, 1));