purescript-supply
A splittable value supply for Purescript
Usage
spago install supplyThen you can use the functions in Supply module. Example -
main :: Effect Unit
main = withSupply \s -> do
let (v1 /\ v2 /\ v3 /\ v4 /\ _) = split4 s
let (v5 /\ v6 /\ v7 /\ v8 /\ _) = split4 v2
log $ show $ supplyValue v1
log $ show $ supplyValue v8
log $ show $ supplyValue v3The supplied values are sequential integers that are lazily resolved when they are used. So this should print -
0
1
2
API
Creating a new Supply
Effectful interface -
newSupply :: forall a. a -> (a -> a) -> Effect (Supply a)Or pure interface -
withSupply :: forall r. (Supply Int -> r) -> rGetting the current value from a supply
supplyValue :: forall a. Supply a -> aEach supply can only provide a single value. Repeatedly calling supplyValue on the same supply will give the same result.
Splitting Supplies
To get multiple values, supplies can be split any number of times.
-- | Split a supply into two different supplies.
-- The resulting supplies are different from the input supply.
split2 :: forall a. Supply a -> Tuple (Supply a) (Supply a)
-- | Split a supply into three different supplies.
split3 :: forall a. Supply a -> Tuple3 (Supply a) (Supply a) (Supply a)
-- | Split a supply into four different supplies.
split4 :: forall a. Supply a -> Tuple4 (Supply a) (Supply a) (Supply a) (Supply a)Modifying supplies
Supply has a Functor instance.
Also supplies have a comonad instance so you can use modifySupply a.k.a. cobind.
-- | Generate a new supply by systematically applying a function to an existing supply
modifySupply :: forall a b. Supply a -> (Supply a -> b) -> Supply b
