Run

newtype Run r a

An extensible effect Monad, indexed by a set of effect functors. Effects are eliminated by interpretation into a pure value or into some base effect Monad.

An example using State and Except:

type MyEffects =
  ( state ∷ STATE Int
  , except ∷ EXCEPT String
  , eff ∷ EFF (console ∷ CONSOLE)
  )

yesProgram ∷ Run MyEffects Unit
yesProgram = do
  whenM (gets (_ < 0)) do
    throw "Number is less than 0"
  whileM_ (gets (_ > 0)) do
    liftEff $ log "Yes"
    modify (_ - 1)

main =
  yesProgram
    # catch (liftEff <<< log)
    # runState 10
    # runBaseEff
    # void

Constructors

• Run (Free (VariantF r) a)

Instances

• Newtype (Run r a) _
• Functor (Run r)
• Apply (Run r)
• Applicative (Run r)
• Bind (Run r)
• Monad (Run r)
• MonadRec (Run r)

  This instance is provided for compatibility, but is otherwise unnecessary. You can use monadic recursion with Run, deferring the MonadRec constraint till it is interpretted.

• (TypeEquals (RProxy r1) (RProxy (effect :: EFFECT | r2))) => MonadEffect (Run r1)
• (TypeEquals (RProxy r1) (RProxy (aff :: AFF, effect :: EFFECT | r2))) => MonadAff (Run r1)

  This will insert an EFF effect because MonadAff entails MonadEff. If you don't want this, use Run.liftAff rather than Control.Monad.Aff.Class.liftAff.

• (TypeEquals (RProxy r1) (RProxy (choose :: CHOOSE | r2))) => Alt (Run r1)
• (TypeEquals (RProxy r1) (RProxy (choose :: CHOOSE | r2))) => Plus (Run r1)
• (TypeEquals (RProxy r1) (RProxy (choose :: CHOOSE | r2))) => Alternative (Run r1)

lift :: forall a f r2 r1 sym. Cons sym (FProxy f) r1 r2 => IsSymbol sym => Functor f => SProxy sym -> f a -> Run r2 a

Lifts an effect functor into the Run Monad according to the provided SProxy slot.

send :: forall r a. VariantF r a -> Run r a

Enqueues an instruction in the Run Monad.

extract :: forall a. Run () a -> a

Extracts the value from a purely interpreted program.

interpret :: forall r a m. Monad m => ((VariantF r) ~> m) -> Run r a -> m a

Extracts the value from a program via some Monad m. This assumes stack safety under Monadic recursion.

interpretRec :: forall r a m. MonadRec m => ((VariantF r) ~> m) -> Run r a -> m a

Extracts the value from a program via some MonadRec m, preserving stack safety.

run :: forall r a m. Monad m => (VariantF r (Run r a) -> m (Run r a)) -> Run r a -> m a

Identical to interpret but with a less restrictive type signature, letting you intercept the rest of the program.

runRec :: forall r a m. MonadRec m => (VariantF r (Run r a) -> m (Run r a)) -> Run r a -> m a

Identical to interpretRec but with a less restrictive type signature, letting you intercept the rest of the program.

runCont :: forall r b a m. (VariantF r (m b) -> m b) -> (a -> m b) -> Run r a -> m b

Extracts the value from a program via some m using continuation passing.

runPure :: forall a r2 r1. (VariantF r1 (Run r1 a) -> Step (Run r1 a) (VariantF r2 (Run r1 a))) -> Run r1 a -> Run r2 a

Eliminates effects purely. Uses Step from Control.Monad.Rec.Class to preserve stack safety under tail recursion.

runAccum :: forall a s r m. Monad m => (s -> VariantF r (Run r a) -> m (Tuple s (Run r a))) -> s -> Run r a -> m a

Extracts the value from a program via some Monad m with an internal accumulator. This assumes stack safety under Monadic recursion.

runAccumRec :: forall a s r m. MonadRec m => (s -> VariantF r (Run r a) -> m (Tuple s (Run r a))) -> s -> Run r a -> m a

Extracts the value from a program via some MonadRec m with an internal accumulator.

runAccumCont :: forall b a s r m. (s -> VariantF r (s -> m b) -> m b) -> (s -> a -> m b) -> s -> Run r a -> m b

Extracts the value from a program via some m using continuation passing with an internal accumulator.

runAccumPure :: forall s b a r2 r1. (s -> VariantF r1 (Run r1 a) -> Step (Tuple s (Run r1 a)) (VariantF r2 (Run r1 a))) -> (s -> a -> b) -> s -> Run r1 a -> Run r2 b

Eliminates effects purely with an internal accumulator. Uses Step from Control.Monad.Rec.Class to preserve stack safety under tail recursion.

peel :: forall r a. Run r a -> Either (VariantF r (Run r a)) a

Reflects the next instruction or the final value if there are no more instructions.

resume :: forall r b a. (VariantF r (Run r a) -> b) -> (a -> b) -> Run r a -> b

Eliminator for the Run data type.

expand :: forall a rx r2 r1. Union r1 rx r2 => Run r1 a -> Run r2 a

Casts some set of effects to a wider set of effects via a left-biased union. For example, you could take a closed effect and unify it with a superset of effects because we know the additional effects never occur.

type LessRows = (foo :: FOO)
type MoreRows = (foo :: FOO, bar :: BAR, baz :: BAZ)

foo :: Run LessRows Unit
foo = foo

foo' :: Run MoreRows Unit
foo' = expand foo

type EFFECT = FProxy Effect

Type synonym for using Eff as an effect.

type AFF = FProxy Aff

Type synonym for using Aff as an effect.

liftEffect :: forall r. Effect ~> (Run (effect :: EFFECT | r))

liftAff :: forall r. Aff ~> (Run (aff :: AFF | r))

Lift an Aff effect into the Run Monad via the aff label.

runBaseEffect :: (Run (effect :: EFFECT)) ~> Effect

Runs a base Eff effect.

runBaseAff :: (Run (aff :: AFF)) ~> Aff

Runs a base Aff effect.

runBaseAff' :: (Run (aff :: AFF, effect :: EFFECT)) ~> Aff

Runs base Aff and Eff together as one effect.

data Step a b

The result of a computation: either Loop containing the updated accumulator, or Done containing the final result of the computation.

Constructors

• Loop a
• Done b

Instances

• Functor (Step a)
• Bifunctor Step

data VariantF (f :: Row Type) a

Instances

• Functor (VariantF r)
• (RowToList r rl, VariantTags rl, VariantFShows rl a, Show a) => Show (VariantF r a)

data FProxy (a :: Type -> Type)

Proxy for a Functor.

Constructors

• FProxy

onMatch :: forall b a r3 r2 r1 r rl. RowToList r rl => VariantFMatchCases rl r1 a b => Union r1 r2 r3 => Record r -> (VariantF r2 a -> b) -> VariantF r3 a -> b

Match a VariantF with a Record containing functions for handling cases. This is similar to on, except instead of providing a single label and handler, you can provide a record where each field maps to a particular VariantF case.

onMatch
 { foo: \foo -> "Foo: " <> maybe "nothing" id foo
 , bar: \bar -> "Bar: " <> snd bar
 }

Polymorphic functions in records (such as show or id) can lead to inference issues if not all polymorphic variables are specified in usage. When in doubt, label methods with specific types, such as show :: Int -> String, or give the whole record an appropriate type.

on :: forall r2 r1 b a f sym. Cons sym (FProxy f) r1 r2 => IsSymbol sym => SProxy sym -> (f a -> b) -> (VariantF r1 a -> b) -> VariantF r2 a -> b

Attempt to read a variant at a given label by providing branches. The failure branch receives the provided variant, but with the label removed.

match :: forall b a r2 r1 r rl. RowToList r rl => VariantFMatchCases rl r1 a b => Union r1 () r2 => Record r -> VariantF r2 a -> b

Combinator for exhaustive pattern matching using an onMatch case record.

matchFn :: VariantF (foo :: FProxy Maybe, bar :: FProxy (Tuple String), baz :: FProxy (Either String)) Int -> String
matchFn = match
 { foo: \foo -> "Foo: " <> maybe "nothing" show foo
 , bar: \bar -> "Bar: " <> show (snd bar)
 , baz: \baz -> "Baz: " <> either id show baz
 }

inj :: forall r2 r1 a f sym. Cons sym (FProxy f) r1 r2 => IsSymbol sym => Functor f => SProxy sym -> f a -> VariantF r2 a

Inject into the variant at a given label.

maybeAtFoo :: forall r. VariantF (foo :: FProxy Maybe | r) Int
maybeAtFoo = inj (SProxy :: SProxy "foo") (Just 42)

default :: forall r b a. a -> VariantF r b -> a

Combinator for partial matching with a default value in case of failure.

caseFn :: forall r. VariantF (foo :: FProxy Maybe, bar :: FProxy (Tuple String) | r) Int -> String
caseFn = default "No match"
 # on (SProxy :: SProxy "foo") (\foo -> "Foo: " <> maybe "nothing" show foo)
 # on (SProxy :: SProxy "bar") (\bar -> "Bar: " <> show (snd bar))

case_ :: forall b a. VariantF () a -> b

Combinator for exhaustive pattern matching.

caseFn :: VariantF (foo :: FProxy Maybe, bar :: FProxy (Tuple String), baz :: FProxy (Either String)) Int -> String
caseFn = case_
 # on (SProxy :: SProxy "foo") (\foo -> "Foo: " <> maybe "nothing" show foo)
 # on (SProxy :: SProxy "bar") (\bar -> "Bar: " <> show (snd bar))
 # on (SProxy :: SProxy "baz") (\baz -> "Baz: " <> either id show baz)

data SProxy (sym :: Symbol)

A value-level proxy for a type-level symbol.

Constructors

• SProxy