Module

Control.Apply

#Apply 

class (Functor f) <= Apply f  where

The Apply class provides the (<*>) which is used to apply a function to an argument under a type constructor.

Apply can be used to lift functions of two or more arguments to work on values wrapped with the type constructor f. It might also be understood in terms of the lift2 function:

lift2 :: forall f a b c. Apply f => (a -> b -> c) -> f a -> f b -> f c
lift2 f a b = f <$> a <*> b

(<*>) is recovered from lift2 as lift2 ($). That is, (<*>) lifts the function application operator ($) to arguments wrapped with the type constructor f.

Instances must satisfy the following law in addition to the Functor laws:

  • Associative composition: (<<<) <$> f <*> g <*> h = f <*> (g <*> h)

Formally, Apply represents a strong lax semi-monoidal endofunctor.

Members

  • apply :: forall a b. f (a -> b) -> f a -> f b

Instances

#(<*>)

Operator alias for Control.Apply.apply (left-associative / precedence 4)

#applyFirst 

applyFirst :: forall a b f. Apply f => f a -> f b -> f a

Combine two effectful actions, keeping only the result of the first.

#(<*)

Operator alias for Control.Apply.applyFirst (left-associative / precedence 4)

#applySecond 

applySecond :: forall a b f. Apply f => f a -> f b -> f b

Combine two effectful actions, keeping only the result of the second.

#(*>)

Operator alias for Control.Apply.applySecond (left-associative / precedence 4)

#lift2 

lift2 :: forall a b c f. Apply f => (a -> b -> c) -> f a -> f b -> f c

Lift a function of two arguments to a function which accepts and returns values wrapped with the type constructor f.

#lift3 

lift3 :: forall a b c d f. Apply f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d

Lift a function of three arguments to a function which accepts and returns values wrapped with the type constructor f.

#lift4 

lift4 :: forall a b c d e f. Apply f => (a -> b -> c -> d -> e) -> f a -> f b -> f c -> f d -> f e

Lift a function of four arguments to a function which accepts and returns values wrapped with the type constructor f.

#lift5 

lift5 :: forall a b c d e f g. Apply f => (a -> b -> c -> d -> e -> g) -> f a -> f b -> f c -> f d -> f e -> f g

Lift a function of five arguments to a function which accepts and returns values wrapped with the type constructor f.

Re-exports from Data.Functor

#Functor 

class Functor f  where

A Functor is a type constructor which supports a mapping operation map.

map can be used to turn functions a -> b into functions f a -> f b whose argument and return types use the type constructor f to represent some computational context.

Instances must satisfy the following laws:

  • Identity: map identity = identity
  • Composition: map (f <<< g) = map f <<< map g

Members

  • map :: forall a b. (a -> b) -> f a -> f b

Instances

#void 

void :: forall f a. Functor f => f a -> f Unit

The void function is used to ignore the type wrapped by a Functor, replacing it with Unit and keeping only the type information provided by the type constructor itself.

void is often useful when using do notation to change the return type of a monadic computation:

main = forE 1 10 \n -> void do
  print n
  print (n * n)

#(<$>)

Operator alias for Data.Functor.map (left-associative / precedence 4)

#(<$)

Operator alias for Data.Functor.voidRight (left-associative / precedence 4)

#(<#>)

Operator alias for Data.Functor.mapFlipped (left-associative / precedence 1)

#($>)

Operator alias for Data.Functor.voidLeft (left-associative / precedence 4)

Modules