How do I write a monad? It should be pretty simple to port a simple
haskell monad over, but I'm running into an assert error. I think I'm
not passing in the right type function. Here's the monad typeclass:
######################################################
typeclass Monad [M: TYPE->TYPE] {
virtual fun bind[a,b]: M a * (a -> M b) -> M b;
virtual fun ret[a]: a -> M a;
}
######################################################
And here's my instance:
######################################################
#import <flx.flxh>
instance Monad[opt] {
fun bind[a,b] (o:opt[a], f:a -> opt[b]): opt[b] =>
match o with
| None[a] => None[b]
| Some ?x => f x
endmatch
;
fun ret[a] (x:a): opt[a] => Some x;
}
open[T] Monad[opt[T]];
######################################################
This errors out with:
EXCEPTION
File "./lpsrc/flx_lookup.ipk", line 1702, characters 6-12: Assertion failed
(and on a side note, this tiny little code block takes 60s to compile
with dypgen (!). I didn't realize we had that much of a slowdown!)
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