git.iko.soy/Idris-dev
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an Applicative instance for StateT s f where f is a Monad.
455b962startling
lib/Control/Monad/State.idr+7
compare with master
unifiedsplit
@@ -19,6 +19,13 @@ instance Functor f => Functor (StateT s f) where
19 mapFst : (a -> x) -> (a, b) -> (x, b)
19 mapFst : (a -> x) -> (a, b) -> (x, b)
20 mapFst fn (a, b) = (fn a, b)
20 mapFst fn (a, b) = (fn a, b)
21
21
22+instance Monad f => Applicative (StateT s f) where
23+ pure x = ST (\st => pure (x, st))
24+
25+ (ST f) <$> (ST a) = ST (\st => do (g, r) <- f st
26+ (b, t) <- a r
27+ return (g b, t))
28+
22instance Monad m => Monad (StateT s m) where
29instance Monad m => Monad (StateT s m) where
23 return x = ST (\st => return (x, st))
30 return x = ST (\st => return (x, st))
24
31