Thank your for your input! I changed it to the following and in seems to do
what I want now:
datatype result x a =
Ok of a
| Err of x
fun mreturn [x] [a] (r : a) : result x a = Ok r
fun mbind [x] [a] [b] (r : result x a) (f : a -> result x b) : result x b =
case r of
Ok r => f r
|
In this case, I think the straightforward answer is that result is
clearly not a monad, just on the basis of its kind! However, for any
fixed x, fn a => result a x can be a monad. I suggest reformulating
your last definition to be polymorphic in that way. Probably everything
resolves most
I try to create a monad:
datatype result a x =
Ok of a
| Err of x
fun mreturn [a] [x] (r : a) : result a x = Ok r
fun mbind [a] [b] [x] (r : result a x) (f : a -> result b x) : result b x =
case r of
Ok r => f r
| Err x => Err x
val result_monad = mkMonad
{
