Control.Effect.Choose

Nondeterministically choose between two computations.

(m <|> n) >>= k = (m >>= k) <|> (n >>= k)

(m <|> n) <|> o = m <|> (n <|> o)

empty <|> m = m

m <|> empty = m

Select between Just the result of an operation, and Nothing.

optional empty = pure Nothing

optional (pure a) = pure (Just a)

Zero or more.

many m = some m <|> pure []

One or more.

some m = (:) <$> m <*> many m

One or more, returning a NonEmpty list of the results.

some1 m = (:|) <$> m <*> many m

The class of carriers (results) for algebras (effect handlers) over signatures (effects), whose actions are given by the alg method.

m is a carrier for sig containing eff.

Note that if eff is a sum, it will be decomposed into multiple Member constraints. While this technically allows one to combine multiple unrelated effects into a single Has constraint, doing so has two significant drawbacks:

1. Due to a problem with recursive type families, this can lead to significantly slower compiles.

2. It defeats ghc’s warnings for redundant constraints, and thus can lead to a proliferation of redundant constraints as code is changed.

Run an action exhausted of effects to produce its final result value.