Whine.Prelude

guard :: forall m. Alternative m => Boolean -> m Unit

Fail using Plus if a condition does not hold, or succeed using Applicative if it does.

For example:

import Prelude
import Control.Alternative (guard)
import Data.Array ((..))

factors :: Int -> Array Int
factors n = do
  a <- 1..n
  b <- 1..n
  guard $ a * b == n
  pure a

Operator alias for Control.Alt.alt (right-associative / precedence 3)

try :: forall e m a. MonadError e m => m a -> m (Either e a)

Return Right if the given action succeeds, Left if it throws.

runExceptT :: forall e m a. ExceptT e m a -> m (Either e a)

The inverse of ExceptT. Run a computation in the ExceptT monad.

runExcept :: forall e a. Except e a -> Either e a

Run a computation in the Except monad. The inverse of except.

mapExceptT :: forall e e' m n a b. (m (Either e a) -> n (Either e' b)) -> ExceptT e m a -> ExceptT e' n b

Transform the unwrapped computation using the given function.

mapExcept :: forall e e' a b. (Either e a -> Either e' b) -> Except e a -> Except e' b

Transform the unwrapped computation using the given function.

newtype WriterT :: Type -> (Type -> Type) -> Type -> Typenewtype WriterT w m a

The writer monad transformer.

This monad transformer extends the base monad with a monoidal accumulator of type w.

The MonadWriter type class describes the operations supported by this monad.

Instances

• Newtype (WriterT w m a) _
• (Functor m) => Functor (WriterT w m)
• (Semigroup w, Apply m) => Apply (WriterT w m)
• (Monoid w, Applicative m) => Applicative (WriterT w m)
• (Alt m) => Alt (WriterT w m)
• (Plus m) => Plus (WriterT w m)
• (Monoid w, Alternative m) => Alternative (WriterT w m)
• (Semigroup w, Bind m) => Bind (WriterT w m)
• (Monoid w, Monad m) => Monad (WriterT w m)
• (Monoid w, MonadRec m) => MonadRec (WriterT w m)
• (Monoid w, MonadPlus m) => MonadPlus (WriterT w m)
• (Monoid w) => MonadTrans (WriterT w)
• (Monoid w, MonadEffect m) => MonadEffect (WriterT w m)
• (Monoid w, MonadCont m) => MonadCont (WriterT w m)
• (Monoid w, MonadThrow e m) => MonadThrow e (WriterT w m)
• (Monoid w, MonadError e m) => MonadError e (WriterT w m)
• (Monoid w, MonadAsk r m) => MonadAsk r (WriterT w m)
• (Monoid w, MonadReader r m) => MonadReader r (WriterT w m)
• (Monoid w, MonadState s m) => MonadState s (WriterT w m)
• (Monoid w, Monad m) => MonadTell w (WriterT w m)
• (Monoid w, Monad m) => MonadWriter w (WriterT w m)
• (Apply m, Semigroup w, Semigroup a) => Semigroup (WriterT w m a)
• (Applicative m, Monoid w, Monoid a) => Monoid (WriterT w m a)
• (Monoid w, MonadST s m) => MonadST s (WriterT w m)

class MonadWriter :: Type -> (Type -> Type) -> Constraintclass (Monoid w, MonadTell w m) <= MonadWriter w m | m -> w

An extension of the MonadTell class that introduces some operations on the accumulator:

• listen modifies the result to include the changes to the accumulator.
• pass applies the returned function to the accumulator.

An implementation is provided for WriterT, and for other monad transformers defined in this library.

Laws in addition to the MonadTell law:

• do { tell x ; tell y } = tell (x <> y)
• listen (pure a) = pure (Tuple a mempty)
• listen (writer a x) = tell x $> Tuple a x

tell :: forall w m. MonadTell w m => w -> m Unit

mapWriterT :: forall w1 w2 m1 m2 a b. (m1 (Tuple a w1) -> m2 (Tuple b w2)) -> WriterT w1 m1 a -> WriterT w2 m2 b

Change the accumulator and base monad types in a WriterT monad action.

execWriterT :: forall w m a. Functor m => WriterT w m a -> m w

Run a computation in the WriterT monad, discarding the result.

zipWith :: forall a b c. (a -> b -> c) -> Array a -> Array b -> Array c

Apply a function to pairs of elements at the same index in two arrays, collecting the results in a new array.

If one array is longer, elements will be discarded from the longer array.

For example

zipWith (*) [1, 2, 3] [4, 5, 6, 7] == [4, 10, 18]

zip :: forall a b. Array a -> Array b -> Array (Tuple a b)

Takes two arrays and returns an array of corresponding pairs. If one input array is short, excess elements of the longer array are discarded.

zip [1, 2, 3] ["a", "b"] = [Tuple 1 "a", Tuple 2 "b"]

uncons :: forall a. Array a -> Maybe { head :: a, tail :: Array a }

Break an array into its first element and remaining elements.

Using uncons provides a way of writing code that would use cons patterns in Haskell or pre-PureScript 0.7:

f (x : xs) = something
f [] = somethingElse

Becomes:

f arr = case uncons arr of
  Just { head: x, tail: xs } -> something
  Nothing -> somethingElse

take :: forall a. Int -> Array a -> Array a

Keep only a number of elements from the start of an array, creating a new array.

letters = ["a", "b", "c"]

take 2 letters = ["a", "b"]
take 100 letters = ["a", "b", "c"]

partition :: forall a. (a -> Boolean) -> Array a -> { no :: Array a, yes :: Array a }

Partition an array using a predicate function, creating a set of new arrays. One for the values satisfying the predicate function and one for values that don't.

partition (_ > 0) [-1, 4, -5, 7] = { yes: [4, 7], no: [-1, -5] }

null :: forall a. Array a -> Boolean

Test whether an array is empty.

null [] = true
null [1, 2] = false

nub :: forall a. Ord a => Array a -> Array a

Remove the duplicates from an array, creating a new array.

nub [1, 2, 1, 3, 3] = [1, 2, 3]

mapMaybe :: forall a b. (a -> Maybe b) -> Array a -> Array b

Apply a function to each element in an array, keeping only the results which contain a value, creating a new array.

parseEmail :: String -> Maybe Email
parseEmail = ...

mapMaybe parseEmail ["a.com", "hello@example.com", "--"]
   = [Email {user: "hello", domain: "example.com"}]

length :: forall a. Array a -> Int

Get the number of elements in an array.

length ["Hello", "World"] = 2

last :: forall a. Array a -> Maybe a

Get the last element in an array, or Nothing if the array is empty

Running time: O(1).

last [1, 2] = Just 2
last [] = Nothing

filter :: forall a. (a -> Boolean) -> Array a -> Array a

Filter an array, keeping the elements which satisfy a predicate function, creating a new array.

filter (_ > 0) [-1, 4, -5, 7] = [4, 7]

elem :: forall a. Eq a => a -> Array a -> Boolean

Returns true if the array has the given element.

drop :: forall a. Int -> Array a -> Array a

Drop a number of elements from the start of an array, creating a new array.

letters = ["a", "b", "c", "d"]

drop 2 letters = ["c", "d"]
drop 10 letters = []

cons :: forall a. a -> Array a -> Array a

Attaches an element to the front of an array, creating a new array.

cons 1 [2, 3, 4] = [1, 2, 3, 4]

Note, the running time of this function is O(n).

catMaybes :: forall a. Array (Maybe a) -> Array a

Filter an array of optional values, keeping only the elements which contain a value, creating a new array.

catMaybes [Nothing, Just 2, Nothing, Just 4] = [2, 4]

Operator alias for Data.Array.difference (non-associative / precedence 5)

Operator alias for Data.Array.cons (right-associative / precedence 6)

An infix alias for cons.

1 : [2, 3, 4] = [1, 2, 3, 4]

Note, the running time of this function is O(n).

Operator alias for Data.Array.range (non-associative / precedence 8)

An infix synonym for range.

2 .. 5 = [2, 3, 4, 5]

newtype NonEmptyArray a

An array that is known not to be empty.

You can use the constructor to create a NonEmptyArray that isn't non-empty, breaking the guarantee behind this newtype. It is provided as an escape hatch mainly for the Data.Array.NonEmpty and Data.Array modules. Use this at your own risk when you know what you are doing.

Instances

• (Show a) => Show (NonEmptyArray a)
• (Eq a) => Eq (NonEmptyArray a)
• Eq1 NonEmptyArray
• (Ord a) => Ord (NonEmptyArray a)
• Ord1 NonEmptyArray
• Semigroup (NonEmptyArray a)
• Functor NonEmptyArray
• FunctorWithIndex Int NonEmptyArray
• Foldable NonEmptyArray
• FoldableWithIndex Int NonEmptyArray
• Foldable1 NonEmptyArray
• Unfoldable1 NonEmptyArray
• Traversable NonEmptyArray
• TraversableWithIndex Int NonEmptyArray
• Traversable1 NonEmptyArray
• Apply NonEmptyArray
• Applicative NonEmptyArray
• Bind NonEmptyArray
• Monad NonEmptyArray
• Alt NonEmptyArray

bimap :: forall f a b c d. Bifunctor f => (a -> b) -> (c -> d) -> f a c -> f b d

rmap :: forall f a b c. Bifunctor f => (b -> c) -> f a b -> f a c

Map a function over the second type arguments of a Bifunctor.

lmap :: forall f a b c. Bifunctor f => (a -> b) -> f a c -> f b c

Map a function over the first type argument of a Bifunctor.

data Either a b

The Either type is used to represent a choice between two types of value.

A common use case for Either is error handling, where Left is used to carry an error value and Right is used to carry a success value.

Constructors

• Left a
• Right b

Instances

• Functor (Either a)

  The Functor instance allows functions to transform the contents of a Right with the <$> operator:

  f <$> Right x == Right (f x)
  

  Left values are untouched:

  f <$> Left y == Left y
  

• Generic (Either a b) _
• Invariant (Either a)
• Apply (Either e)

  The Apply instance allows functions contained within a Right to transform a value contained within a Right using the (<*>) operator:

  Right f <*> Right x == Right (f x)
  

  Left values are left untouched:

  Left f <*> Right x == Left f
  Right f <*> Left y == Left y
  

  Combining Functor's <$> with Apply's <*> can be used to transform a pure function to take Either-typed arguments so f :: a -> b -> c becomes f :: Either l a -> Either l b -> Either l c:

  f <$> Right x <*> Right y == Right (f x y)
  

  The Left-preserving behaviour of both operators means the result of an expression like the above but where any one of the values is Left means the whole result becomes Left also, taking the first Left value found:

  f <$> Left x <*> Right y == Left x
  f <$> Right x <*> Left y == Left y
  f <$> Left x <*> Left y == Left x
  

• Applicative (Either e)

  The Applicative instance enables lifting of values into Either with the pure function:

  pure x :: Either _ _ == Right x
  

  Combining Functor's <$> with Apply's <*> and Applicative's pure can be used to pass a mixture of Either and non-Either typed values to a function that does not usually expect them, by using pure for any value that is not already Either typed:

  f <$> Right x <*> pure y == Right (f x y)
  

  Even though pure = Right it is recommended to use pure in situations like this as it allows the choice of Applicative to be changed later without having to go through and replace Right with a new constructor.

• Alt (Either e)

  The Alt instance allows for a choice to be made between two Either values with the <|> operator, where the first Right encountered is taken.

  Right x <|> Right y == Right x
  Left x <|> Right y == Right y
  Left x <|> Left y == Left y
  

• Bind (Either e)

  The Bind instance allows sequencing of Either values and functions that return an Either by using the >>= operator:

  Left x >>= f = Left x
  Right x >>= f = f x
  

  Either's "do notation" can be understood to work like this:

  x :: forall e a. Either e a
  x = --
  
  y :: forall e b. Either e b
  y = --
  
  foo :: forall e a. (a -> b -> c) -> Either e c
  foo f = do
    x' <- x
    y' <- y
    pure (f x' y')
  

  ...which is equivalent to...

  x >>= (\x' -> y >>= (\y' -> pure (f x' y')))
  

  ...and is the same as writing...

  foo :: forall e a. (a -> b -> c) -> Either e c
  foo f = case x of
    Left e ->
      Left e
    Right x -> case y of
      Left e ->
        Left e
      Right y ->
        Right (f x y)
  

• Monad (Either e)

  The Monad instance guarantees that there are both Applicative and Bind instances for Either.

• Extend (Either e)

  The Extend instance allows sequencing of Either values and functions that accept an Either and return a non-Either result using the <<= operator.

  f <<= Left x = Left x
  f <<= Right x = Right (f (Right x))
  

• (Show a, Show b) => Show (Either a b)

  The Show instance allows Either values to be rendered as a string with show whenever there is an Show instance for both type the Either can contain.

• (Eq a, Eq b) => Eq (Either a b)

  The Eq instance allows Either values to be checked for equality with == and inequality with /= whenever there is an Eq instance for both types the Either can contain.

• (Eq a) => Eq1 (Either a)
• (Ord a, Ord b) => Ord (Either a b)

  The Ord instance allows Either values to be compared with compare, >, >=, < and <= whenever there is an Ord instance for both types the Either can contain.

  Any Left value is considered to be less than a Right value.

• (Ord a) => Ord1 (Either a)
• (Bounded a, Bounded b) => Bounded (Either a b)
• (Semigroup b) => Semigroup (Either a b)

note :: forall a b. a -> Maybe b -> Either a b

Takes a default and a Maybe value, if the value is a Just, turn it into a Right, if the value is a Nothing use the provided default as a Left

note "default" Nothing = Left "default"
note "default" (Just 1) = Right 1

hush :: forall a b. Either a b -> Maybe b

Turns an Either into a Maybe, by throwing potential Left values away and converting them into Nothing. Right values get turned into Justs.

hush (Left "ParseError") = Nothing
hush (Right 42) = Just 42

fromRight :: forall a b. b -> Either a b -> b

A function that extracts the value from the Right data constructor. The first argument is a default value, which will be returned in the case where a Left is passed to fromRight.

either :: forall a b c. (a -> c) -> (b -> c) -> Either a b -> c

Takes two functions and an Either value, if the value is a Left the inner value is applied to the first function, if the value is a Right the inner value is applied to the second function.

either f g (Left x) == f x
either f g (Right y) == g y

foldlWithIndex :: forall i f a b. FoldableWithIndex i f => (i -> b -> a -> b) -> b -> f a -> b

forWithIndex_ :: forall i a b f m. Applicative m => FoldableWithIndex i f => f a -> (i -> a -> m b) -> m Unit

A version of traverseWithIndex_ with its arguments flipped.

This can be useful when running an action written using do notation for every element in a data structure:

For example:

forWithIndex_ ["a", "b", "c"] \i x -> do
  logShow i
  log x

newtype Identity a

Constructors

• Identity a

Instances

• Newtype (Identity a) _
• (Eq a) => Eq (Identity a)
• (Ord a) => Ord (Identity a)
• (Bounded a) => Bounded (Identity a)
• (HeytingAlgebra a) => HeytingAlgebra (Identity a)
• (BooleanAlgebra a) => BooleanAlgebra (Identity a)
• (Semigroup a) => Semigroup (Identity a)
• (Monoid a) => Monoid (Identity a)
• (Semiring a) => Semiring (Identity a)
• (EuclideanRing a) => EuclideanRing (Identity a)
• (Ring a) => Ring (Identity a)
• (CommutativeRing a) => CommutativeRing (Identity a)
• (Lazy a) => Lazy (Identity a)
• (Show a) => Show (Identity a)
• Eq1 Identity
• Ord1 Identity
• Functor Identity
• Invariant Identity
• Alt Identity
• Apply Identity
• Applicative Identity
• Bind Identity
• Monad Identity
• Extend Identity
• Comonad Identity

data Map k v

Map k v represents maps from keys of type k to values of type v.

Instances

• (Eq k) => Eq1 (Map k)
• (Eq k, Eq v) => Eq (Map k v)
• (Ord k) => Ord1 (Map k)
• (Ord k, Ord v) => Ord (Map k v)
• (Show k, Show v) => Show (Map k v)
• (Warn (Text "Data.Map\'s `Semigroup` instance is now unbiased and differs from the left-biased instance defined in PureScript releases <= 0.13.x."), Ord k, Semigroup v) => Semigroup (Map k v)
• (Warn (Text "Data.Map\'s `Semigroup` instance is now unbiased and differs from the left-biased instance defined in PureScript releases <= 0.13.x."), Ord k, Semigroup v) => Monoid (Map k v)
• (Ord k) => Alt (Map k)
• (Ord k) => Plus (Map k)
• Functor (Map k)
• FunctorWithIndex k (Map k)
• (Ord k) => Apply (Map k)
• (Ord k) => Bind (Map k)
• Foldable (Map k)
• FoldableWithIndex k (Map k)
• Traversable (Map k)
• TraversableWithIndex k (Map k)

data Maybe a

The Maybe type is used to represent optional values and can be seen as something like a type-safe null, where Nothing is null and Just x is the non-null value x.

Constructors

• Nothing
• Just a

Instances

• Functor Maybe

  The Functor instance allows functions to transform the contents of a Just with the <$> operator:

  f <$> Just x == Just (f x)
  

  Nothing values are left untouched:

  f <$> Nothing == Nothing
  

• Apply Maybe

  The Apply instance allows functions contained within a Just to transform a value contained within a Just using the apply operator:

  Just f <*> Just x == Just (f x)
  

  Nothing values are left untouched:

  Just f <*> Nothing == Nothing
  Nothing <*> Just x == Nothing
  

  Combining Functor's <$> with Apply's <*> can be used transform a pure function to take Maybe-typed arguments so f :: a -> b -> c becomes f :: Maybe a -> Maybe b -> Maybe c:

  f <$> Just x <*> Just y == Just (f x y)
  

  The Nothing-preserving behaviour of both operators means the result of an expression like the above but where any one of the values is Nothing means the whole result becomes Nothing also:

  f <$> Nothing <*> Just y == Nothing
  f <$> Just x <*> Nothing == Nothing
  f <$> Nothing <*> Nothing == Nothing
  

• Applicative Maybe

  The Applicative instance enables lifting of values into Maybe with the pure function:

  pure x :: Maybe _ == Just x
  

  Combining Functor's <$> with Apply's <*> and Applicative's pure can be used to pass a mixture of Maybe and non-Maybe typed values to a function that does not usually expect them, by using pure for any value that is not already Maybe typed:

  f <$> Just x <*> pure y == Just (f x y)
  

  Even though pure = Just it is recommended to use pure in situations like this as it allows the choice of Applicative to be changed later without having to go through and replace Just with a new constructor.

• Alt Maybe

  The Alt instance allows for a choice to be made between two Maybe values with the <|> operator, where the first Just encountered is taken.

  Just x <|> Just y == Just x
  Nothing <|> Just y == Just y
  Nothing <|> Nothing == Nothing
  

• Plus Maybe

  The Plus instance provides a default Maybe value:

  empty :: Maybe _ == Nothing
  

• Alternative Maybe

  The Alternative instance guarantees that there are both Applicative and Plus instances for Maybe.

• Bind Maybe

  The Bind instance allows sequencing of Maybe values and functions that return a Maybe by using the >>= operator:

  Just x >>= f = f x
  Nothing >>= f = Nothing
  

• Monad Maybe

  The Monad instance guarantees that there are both Applicative and Bind instances for Maybe. This also enables the do syntactic sugar:

  do
    x' <- x
    y' <- y
    pure (f x' y')
  

  Which is equivalent to:

  x >>= (\x' -> y >>= (\y' -> pure (f x' y')))
  

  Which is equivalent to:

  case x of
    Nothing -> Nothing
    Just x' -> case y of
      Nothing -> Nothing
      Just y' -> Just (f x' y')
  

• Extend Maybe

  The Extend instance allows sequencing of Maybe values and functions that accept a Maybe a and return a non-Maybe result using the <<= operator.

  f <<= Nothing = Nothing
  f <<= x = Just (f x)
  

• Invariant Maybe
• (Semigroup a) => Semigroup (Maybe a)

  The Semigroup instance enables use of the operator <> on Maybe values whenever there is a Semigroup instance for the type the Maybe contains. The exact behaviour of <> depends on the "inner" Semigroup instance, but generally captures the notion of appending or combining things.

  Just x <> Just y = Just (x <> y)
  Just x <> Nothing = Just x
  Nothing <> Just y = Just y
  Nothing <> Nothing = Nothing
  

• (Semigroup a) => Monoid (Maybe a)
• (Semiring a) => Semiring (Maybe a)
• (Eq a) => Eq (Maybe a)

  The Eq instance allows Maybe values to be checked for equality with == and inequality with /= whenever there is an Eq instance for the type the Maybe contains.

• Eq1 Maybe
• (Ord a) => Ord (Maybe a)

  The Ord instance allows Maybe values to be compared with compare, >, >=, < and <= whenever there is an Ord instance for the type the Maybe contains.

  Nothing is considered to be less than any Just value.

• Ord1 Maybe
• (Bounded a) => Bounded (Maybe a)
• (Show a) => Show (Maybe a)

  The Show instance allows Maybe values to be rendered as a string with show whenever there is an Show instance for the type the Maybe contains.

• Generic (Maybe a) _

maybe :: forall a b. b -> (a -> b) -> Maybe a -> b

Takes a default value, a function, and a Maybe value. If the Maybe value is Nothing the default value is returned, otherwise the function is applied to the value inside the Just and the result is returned.

maybe x f Nothing == x
maybe x f (Just y) == f y

isNothing :: forall a. Maybe a -> Boolean

Returns true when the Maybe value is Nothing.

isJust :: forall a. Maybe a -> Boolean

Returns true when the Maybe value was constructed with Just.

fromMaybe :: forall a. a -> Maybe a -> a

Takes a default value, and a Maybe value. If the Maybe value is Nothing the default value is returned, otherwise the value inside the Just is returned.

fromMaybe x Nothing == x
fromMaybe x (Just y) == y

wrap :: forall t a. Newtype t a => a -> t

unwrap :: forall t a. Newtype t a => t -> a

un :: forall t a. Newtype t a => (a -> t) -> t -> a

Given a constructor for a Newtype, this returns the appropriate unwrap function.

data Nullable t0

A nullable type. This type constructor is intended to be used for interoperating with JavaScript functions which accept or return null values.

The runtime representation of Nullable T is the same as that of T, except that it may also be null. For example, the JavaScript values null, [], and [1,2,3] may all be given the type Nullable (Array Int). Similarly, the JavaScript values [], [null], and [1,2,null,3] may all be given the type Array (Nullable Int).

There is one pitfall with Nullable, which is that values of the type Nullable T will not function as you might expect if the type T happens to itself permit null as a valid runtime representation.

In particular, values of the type Nullable (Nullable T) will ‘collapse’, in the sense that the PureScript expressions notNull null and null will both leave you with a value whose runtime representation is just null. Therefore it is important to avoid using Nullable T in situations where T itself can take null as a runtime representation. If in doubt, use Maybe instead.

Nullable does not permit lawful Functor, Applicative, or Monad instances as a result of this pitfall, which is why these instances are not provided.

Instances

• (Show a) => Show (Nullable a)
• (Eq a) => Eq (Nullable a)
• Eq1 Nullable
• (Ord a) => Ord (Nullable a)
• Ord1 Nullable

dimap :: forall p a b c d. Profunctor p => (a -> b) -> (c -> d) -> p b c -> p a d

newtype Pattern

A newtype used in cases where there is a string to be matched.

pursPattern = Pattern ".purs"
--can be used like this:
contains pursPattern "Test.purs"
   == true

Constructors

• Pattern String

Instances

• Eq Pattern
• Ord Pattern
• Newtype Pattern _
• Show Pattern

joinWith :: String -> Array String -> String

Joins the strings in the array together, inserting the first argument as separator between them.

joinWith ", " ["apple", "banana", "orange"] == "apple, banana, orange"

newtype NonEmptyString

A string that is known not to be empty.

You can use this constructor to create a NonEmptyString that isn't non-empty, breaking the guarantee behind this newtype. It is provided as an escape hatch mainly for the Data.NonEmpty.CodeUnits and Data.NonEmpty.CodePoints modules. Use this at your own risk when you know what you are doing.

Instances

• Eq NonEmptyString
• Ord NonEmptyString
• Semigroup NonEmptyString
• Show NonEmptyString

sequence :: forall t a m. Traversable t => Applicative m => t (m a) -> m (t a)

traverse :: forall t a b m. Traversable t => Applicative m => (a -> m b) -> t a -> m (t b)

traverse_ :: forall a b f m. Applicative m => Foldable f => (a -> m b) -> f a -> m Unit

Traverse a data structure, performing some effects encoded by an Applicative functor at each value, ignoring the final result.

For example:

traverse_ print [1, 2, 3]

sequence_ :: forall a f m. Applicative m => Foldable f => f (m a) -> m Unit

Perform all of the effects in some data structure in the order given by the Foldable instance, ignoring the final result.

For example:

sequence_ [ trace "Hello, ", trace " world!" ]

intercalate :: forall f m. Foldable f => Monoid m => m -> f m -> m

Fold a data structure, accumulating values in some Monoid, combining adjacent elements using the specified separator.

For example:

> intercalate ", " ["Lorem", "ipsum", "dolor"]
= "Lorem, ipsum, dolor"

> intercalate "*" ["a", "b", "c"]
= "a*b*c"

> intercalate [1] [[2, 3], [4, 5], [6, 7]]
= [2, 3, 1, 4, 5, 1, 6, 7]

for_ :: forall a b f m. Applicative m => Foldable f => f a -> (a -> m b) -> m Unit

A version of traverse_ with its arguments flipped.

This can be useful when running an action written using do notation for every element in a data structure:

For example:

for_ [1, 2, 3] \n -> do
  print n
  trace "squared is"
  print (n * n)

for :: forall a b m t. Applicative m => Traversable t => t a -> (a -> m b) -> m (t b)

A version of traverse with its arguments flipped.

This can be useful when running an action written using do notation for every element in a data structure:

For example:

for [1, 2, 3] \n -> do
  print n
  return (n * n)

fold :: forall f m. Foldable f => Monoid m => f m -> m

Fold a data structure, accumulating values in some Monoid.

any :: forall a b f. Foldable f => HeytingAlgebra b => (a -> b) -> f a -> b

any f is the same as or <<< map f; map a function over the structure, and then get the disjunction of the results.

data Tuple a b

A simple product type for wrapping a pair of component values.

Constructors

• Tuple a b

Instances

• (Show a, Show b) => Show (Tuple a b)

  Allows Tuples to be rendered as a string with show whenever there are Show instances for both component types.

• (Eq a, Eq b) => Eq (Tuple a b)

  Allows Tuples to be checked for equality with == and /= whenever there are Eq instances for both component types.

• (Eq a) => Eq1 (Tuple a)
• (Ord a, Ord b) => Ord (Tuple a b)

  Allows Tuples to be compared with compare, >, >=, < and <= whenever there are Ord instances for both component types. To obtain the result, the fsts are compared, and if they are EQual, the snds are compared.

• (Ord a) => Ord1 (Tuple a)
• (Bounded a, Bounded b) => Bounded (Tuple a b)
• Semigroupoid Tuple
• (Semigroup a, Semigroup b) => Semigroup (Tuple a b)

  The Semigroup instance enables use of the associative operator <> on Tuples whenever there are Semigroup instances for the component types. The <> operator is applied pairwise, so:

  (Tuple a1 b1) <> (Tuple a2 b2) = Tuple (a1 <> a2) (b1 <> b2)
  

• (Monoid a, Monoid b) => Monoid (Tuple a b)
• (Semiring a, Semiring b) => Semiring (Tuple a b)
• (Ring a, Ring b) => Ring (Tuple a b)
• (CommutativeRing a, CommutativeRing b) => CommutativeRing (Tuple a b)
• (HeytingAlgebra a, HeytingAlgebra b) => HeytingAlgebra (Tuple a b)
• (BooleanAlgebra a, BooleanAlgebra b) => BooleanAlgebra (Tuple a b)
• Functor (Tuple a)

  The Functor instance allows functions to transform the contents of a Tuple with the <$> operator, applying the function to the second component, so:

  f <$> (Tuple x y) = Tuple x (f y)
  

• Generic (Tuple a b) _
• Invariant (Tuple a)
• (Semigroup a) => Apply (Tuple a)

  The Apply instance allows functions to transform the contents of a Tuple with the <*> operator whenever there is a Semigroup instance for the fst component, so:

  (Tuple a1 f) <*> (Tuple a2 x) == Tuple (a1 <> a2) (f x)
  

• (Monoid a) => Applicative (Tuple a)
• (Semigroup a) => Bind (Tuple a)
• (Monoid a) => Monad (Tuple a)
• Extend (Tuple a)
• Comonad (Tuple a)
• (Lazy a, Lazy b) => Lazy (Tuple a b)

snd :: forall a b. Tuple a b -> b

Returns the second component of a tuple.

fst :: forall a b. Tuple a b -> a

Returns the first component of a tuple.

Operator alias for Data.Tuple.Tuple (right-associative / precedence 6)

Shorthand for constructing n-tuples as nested pairs. a /\ b /\ c /\ d /\ unit becomes Tuple a (Tuple b (Tuple c (Tuple d unit)))

Operator alias for Data.Tuple.Tuple (right-associative / precedence 6)

Shorthand for constructing n-tuple types as nested pairs. forall a b c d. a /\ b /\ c /\ d /\ Unit becomes forall a b c d. Tuple a (Tuple b (Tuple c (Tuple d Unit)))

data Effect t0

A native effect. The type parameter denotes the return type of running the effect, that is, an Effect Int is a possibly-effectful computation which eventually produces a value of the type Int when it finishes.

Instances

• Functor Effect
• Apply Effect
• Applicative Effect
• Bind Effect
• Monad Effect
• (Semigroup a) => Semigroup (Effect a)

  The Semigroup instance for effects allows you to run two effects, one after the other, and then combine their results using the result type's Semigroup instance.

• (Monoid a) => Monoid (Effect a)

  If you have a Monoid a instance, then mempty :: Effect a is defined as pure mempty.

class MonadEffect :: (Type -> Type) -> Constraintclass (Monad m) <= MonadEffect m  where

The MonadEffect class captures those monads which support native effects.

Instances are provided for Effect itself, and the standard monad transformers.

liftEffect can be used in any appropriate monad transformer stack to lift an action of type Effect a into the monad.

Members

• liftEffect :: forall a. Effect a -> m a

Instances

• MonadEffect Effect

data JSON

A type that represents all varieties of JSON value.

This is not a PureScript sum type, instead the underlying JSON representation is used for efficiency and performance reasons.

Instances

• Eq JSON
• Ord JSON

data Encoding

Constructors

• ASCII
• UTF8
• UTF16LE
• UCS2
• Base64
• Base64Url
• Latin1
• Binary
• Hex

Instances

• Show Encoding

type FilePath = String

Type for strings representing file paths.

newtype Void

An uninhabited data type. In other words, one can never create a runtime value of type Void because no such value exists.

Void is useful to eliminate the possibility of a value being created. For example, a value of type Either Void Boolean can never have a Left value created in PureScript.

This should not be confused with the keyword void that commonly appears in C-family languages, such as Java:

public class Foo {
  void doSomething() { System.out.println("hello world!"); }
}

In PureScript, one often uses Unit to achieve similar effects as the void of C-family languages above.

data Unit

The Unit type has a single inhabitant, called unit. It represents values with no computational content.

Unit is often used, wrapped in a monadic type constructor, as the return type of a computation where only the effects are important.

When returning a value of type Unit from an FFI function, it is recommended to use undefined, or not return a value at all.

data Ordering

The Ordering data type represents the three possible outcomes of comparing two values:

LT - The first value is less than the second. GT - The first value is greater than the second. EQ - The first value is equal to the second.

Constructors

• LT
• GT
• EQ

Instances

• Eq Ordering
• Semigroup Ordering
• Show Ordering

class Applicative :: (Type -> Type) -> Constraintclass (Apply f) <= Applicative f  where

The Applicative type class extends the Apply type class with a pure function, which can be used to create values of type f a from values of type a.

Where Apply provides the ability to lift functions of two or more arguments to functions whose arguments are wrapped using f, and Functor provides the ability to lift functions of one argument, pure can be seen as the function which lifts functions of zero arguments. That is, Applicative functors support a lifting operation for any number of function arguments.

Instances must satisfy the following laws in addition to the Apply laws:

• Identity: (pure identity) <*> v = v
• Composition: pure (<<<) <*> f <*> g <*> h = f <*> (g <*> h)
• Homomorphism: (pure f) <*> (pure x) = pure (f x)
• Interchange: u <*> (pure y) = (pure (_ $ y)) <*> u

Members

• pure :: forall a. a -> f a

Instances

• Applicative (Function r)
• Applicative Array
• Applicative Proxy

class Apply :: (Type -> Type) -> Constraintclass (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.

Put differently...

foo =
  functionTakingNArguments <$> computationProducingArg1
                           <*> computationProducingArg2
                           <*> ...
                           <*> computationProducingArgN

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

• Apply (Function r)
• Apply Array
• Apply Proxy

class Bind :: (Type -> Type) -> Constraintclass (Apply m) <= Bind m  where

The Bind type class extends the Apply type class with a "bind" operation (>>=) which composes computations in sequence, using the return value of one computation to determine the next computation.

The >>= operator can also be expressed using do notation, as follows:

x >>= f = do y <- x
             f y

where the function argument of f is given the name y.

Instances must satisfy the following laws in addition to the Apply laws:

• Associativity: (x >>= f) >>= g = x >>= (\k -> f k >>= g)
• Apply Superclass: apply f x = f >>= \f’ -> map f’ x

Associativity tells us that we can regroup operations which use do notation so that we can unambiguously write, for example:

do x <- m1
   y <- m2 x
   m3 x y

Members

• bind :: forall a b. m a -> (a -> m b) -> m b

Instances

• Bind (Function r)
• Bind Array

  The bind/>>= function for Array works by applying a function to each element in the array, and flattening the results into a single, new array.

  Array's bind/>>= works like a nested for loop. Each bind adds another level of nesting in the loop. For example:

  foo :: Array String
  foo =
    ["a", "b"] >>= \eachElementInArray1 ->
      ["c", "d"] >>= \eachElementInArray2
        pure (eachElementInArray1 <> eachElementInArray2)
  
  -- In other words...
  foo
  -- ... is the same as...
  [ ("a" <> "c"), ("a" <> "d"), ("b" <> "c"), ("b" <> "d") ]
  -- which simplifies to...
  [ "ac", "ad", "bc", "bd" ]
  

• Bind Proxy

class (HeytingAlgebra a) <= BooleanAlgebra a 

The BooleanAlgebra type class represents types that behave like boolean values.

Instances should satisfy the following laws in addition to the HeytingAlgebra law:

• Excluded middle:
  • a || not a = tt

Instances

• BooleanAlgebra Boolean
• BooleanAlgebra Unit
• (BooleanAlgebra b) => BooleanAlgebra (a -> b)
• (RowToList row list, BooleanAlgebraRecord list row row) => BooleanAlgebra (Record row)
• BooleanAlgebra (Proxy a)

class (Ord a) <= Bounded a  where

The Bounded type class represents totally ordered types that have an upper and lower boundary.

Instances should satisfy the following law in addition to the Ord laws:

• Bounded: bottom <= a <= top

Members

• top :: a
• bottom :: a

Instances

• Bounded Boolean
• Bounded Int

  The Bounded Int instance has top :: Int equal to 2^31 - 1, and bottom :: Int equal to -2^31, since these are the largest and smallest integers representable by twos-complement 32-bit integers, respectively.

• Bounded Char

  Characters fall within the Unicode range.

• Bounded Ordering
• Bounded Unit
• Bounded Number
• Bounded (Proxy a)
• (RowToList row list, BoundedRecord list row row) => Bounded (Record row)

class Category :: forall k. (k -> k -> Type) -> Constraintclass (Semigroupoid a) <= Category a  where

Categorys consist of objects and composable morphisms between them, and as such are Semigroupoids, but unlike semigroupoids must have an identity element.

Instances must satisfy the following law in addition to the Semigroupoid law:

• Identity: identity <<< p = p <<< identity = p

Members

• identity :: forall t. a t t

Instances

• Category Function

class (Ring a) <= CommutativeRing a 

The CommutativeRing class is for rings where multiplication is commutative.

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

• Commutative multiplication: a * b = b * a

Instances

• CommutativeRing Int
• CommutativeRing Number
• CommutativeRing Unit
• (CommutativeRing b) => CommutativeRing (a -> b)
• (RowToList row list, CommutativeRingRecord list row row) => CommutativeRing (Record row)
• CommutativeRing (Proxy a)

class Discard a  where

A class for types whose values can safely be discarded in a do notation block.

An example is the Unit type, since there is only one possible value which can be returned.

Members

• discard :: forall f b. Bind f => f a -> (a -> f b) -> f b

Instances

• Discard Unit
• Discard (Proxy a)

class (Ring a) <= DivisionRing a  where

The DivisionRing class is for non-zero rings in which every non-zero element has a multiplicative inverse. Division rings are sometimes also called skew fields.

Instances must satisfy the following laws in addition to the Ring laws:

• Non-zero ring: one /= zero
• Non-zero multiplicative inverse: recip a * a = a * recip a = one for all non-zero a

The result of recip zero is left undefined; individual instances may choose how to handle this case.

If a type has both DivisionRing and CommutativeRing instances, then it is a field and should have a Field instance.

Members

• recip :: a -> a

Instances

• DivisionRing Number

class Eq a  where

The Eq type class represents types which support decidable equality.

Eq instances should satisfy the following laws:

• Reflexivity: x == x = true
• Symmetry: x == y = y == x
• Transitivity: if x == y and y == z then x == z

Note: The Number type is not an entirely law abiding member of this class due to the presence of NaN, since NaN /= NaN. Additionally, computing with Number can result in a loss of precision, so sometimes values that should be equivalent are not.

Members

• eq :: a -> a -> Boolean

Instances

• Eq Boolean
• Eq Int
• Eq Number
• Eq Char
• Eq String
• Eq Unit
• Eq Void
• (Eq a) => Eq (Array a)
• (RowToList row list, EqRecord list row) => Eq (Record row)
• Eq (Proxy a)

class (CommutativeRing a) <= EuclideanRing a  where

The EuclideanRing class is for commutative rings that support division. The mathematical structure this class is based on is sometimes also called a Euclidean domain.

Instances must satisfy the following laws in addition to the Ring laws:

• Integral domain: one /= zero, and if a and b are both nonzero then so is their product a * b
• Euclidean function degree:
  • Nonnegativity: For all nonzero a, degree a >= 0
  • Quotient/remainder: For all a and b, where b is nonzero, let q = a / b and r = a `mod` b; then a = q*b + r, and also either r = zero or degree r < degree b
• Submultiplicative euclidean function:
  • For all nonzero a and b, degree a <= degree (a * b)

The behaviour of division by zero is unconstrained by these laws, meaning that individual instances are free to choose how to behave in this case. Similarly, there are no restrictions on what the result of degree zero is; it doesn't make sense to ask for degree zero in the same way that it doesn't make sense to divide by zero, so again, individual instances may choose how to handle this case.

For any EuclideanRing which is also a Field, one valid choice for degree is simply const 1. In fact, unless there's a specific reason not to, Field types should normally use this definition of degree.

The EuclideanRing Int instance is one of the most commonly used EuclideanRing instances and deserves a little more discussion. In particular, there are a few different sensible law-abiding implementations to choose from, with slightly different behaviour in the presence of negative dividends or divisors. The most common definitions are "truncating" division, where the result of a / b is rounded towards 0, and "Knuthian" or "flooring" division, where the result of a / b is rounded towards negative infinity. A slightly less common, but arguably more useful, option is "Euclidean" division, which is defined so as to ensure that a `mod` b is always nonnegative. With Euclidean division, a / b rounds towards negative infinity if the divisor is positive, and towards positive infinity if the divisor is negative. Note that all three definitions are identical if we restrict our attention to nonnegative dividends and divisors.

In versions 1.x, 2.x, and 3.x of the Prelude, the EuclideanRing Int instance used truncating division. As of 4.x, the EuclideanRing Int instance uses Euclidean division. Additional functions quot and rem are supplied if truncating division is desired.

Members

• degree :: a -> Int
• div :: a -> a -> a
• mod :: a -> a -> a

Instances

• EuclideanRing Int
• EuclideanRing Number

class (EuclideanRing a, DivisionRing a) <= Field a 

The Field class is for types that are (commutative) fields.

Mathematically, a field is a ring which is commutative and in which every nonzero element has a multiplicative inverse; these conditions correspond to the CommutativeRing and DivisionRing classes in PureScript respectively. However, the Field class has EuclideanRing and DivisionRing as superclasses, which seems like a stronger requirement (since CommutativeRing is a superclass of EuclideanRing). In fact, it is not stronger, since any type which has law-abiding CommutativeRing and DivisionRing instances permits exactly one law-abiding EuclideanRing instance. We use a EuclideanRing superclass here in order to ensure that a Field constraint on a function permits you to use div on that type, since div is a member of EuclideanRing.

This class has no laws or members of its own; it exists as a convenience, so a single constraint can be used when field-like behaviour is expected.

This module also defines a single Field instance for any type which has both EuclideanRing and DivisionRing instances. Any other instance would overlap with this instance, so no other Field instances should be defined in libraries. Instead, simply define EuclideanRing and DivisionRing instances, and this will permit your type to be used with a Field constraint.

Instances

• (EuclideanRing a, DivisionRing a) => Field a

class Functor :: (Type -> Type) -> Constraintclass 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

• Functor (Function r)
• Functor Array
• Functor Proxy

class HeytingAlgebra a  where

The HeytingAlgebra type class represents types that are bounded lattices with an implication operator such that the following laws hold:

• Associativity:
  • a || (b || c) = (a || b) || c
  • a && (b && c) = (a && b) && c
• Commutativity:
  • a || b = b || a
  • a && b = b && a
• Absorption:
  • a || (a && b) = a
  • a && (a || b) = a
• Idempotent:
  • a || a = a
  • a && a = a
• Identity:
  • a || ff = a
  • a && tt = a
• Implication:
  • a `implies` a = tt
  • a && (a `implies` b) = a && b
  • b && (a `implies` b) = b
  • a `implies` (b && c) = (a `implies` b) && (a `implies` c)
• Complemented:
  • not a = a `implies` ff

Members

• conj :: a -> a -> a
• disj :: a -> a -> a
• not :: a -> a

Instances

• HeytingAlgebra Boolean
• HeytingAlgebra Unit
• (HeytingAlgebra b) => HeytingAlgebra (a -> b)
• HeytingAlgebra (Proxy a)
• (RowToList row list, HeytingAlgebraRecord list row row) => HeytingAlgebra (Record row)

class Monad :: (Type -> Type) -> Constraintclass (Applicative m, Bind m) <= Monad m 

The Monad type class combines the operations of the Bind and Applicative type classes. Therefore, Monad instances represent type constructors which support sequential composition, and also lifting of functions of arbitrary arity.

Instances must satisfy the following laws in addition to the Applicative and Bind laws:

• Left Identity: pure x >>= f = f x
• Right Identity: x >>= pure = x

Instances

• Monad (Function r)
• Monad Array
• Monad Proxy

class (Semigroup m) <= Monoid m  where

A Monoid is a Semigroup with a value mempty, which is both a left and right unit for the associative operation <>:

• Left unit: (mempty <> x) = x
• Right unit: (x <> mempty) = x

Monoids are commonly used as the result of fold operations, where <> is used to combine individual results, and mempty gives the result of folding an empty collection of elements.

Newtypes for Monoid

Some types (e.g. Int, Boolean) can implement multiple law-abiding instances for Monoid. Let's use Int as an example

1. <> could be + and mempty could be 0
2. <> could be * and mempty could be 1.

To clarify these ambiguous situations, one should use the newtypes defined in Data.Monoid.<NewtypeName> modules.

In the above ambiguous situation, we could use Additive for the first situation or Multiplicative for the second one.

Members

• mempty :: m

Instances

• Monoid Unit
• Monoid Ordering
• (Monoid b) => Monoid (a -> b)
• Monoid String
• Monoid (Array a)
• (RowToList row list, MonoidRecord list row row) => Monoid (Record row)

class (Eq a) <= Ord a  where

The Ord type class represents types which support comparisons with a total order.

Ord instances should satisfy the laws of total orderings:

• Reflexivity: a <= a
• Antisymmetry: if a <= b and b <= a then a == b
• Transitivity: if a <= b and b <= c then a <= c

Note: The Number type is not an entirely law abiding member of this class due to the presence of NaN, since NaN <= NaN evaluates to false

Members

• compare :: a -> a -> Ordering

Instances

• Ord Boolean
• Ord Int
• Ord Number
• Ord String
• Ord Char
• Ord Unit
• Ord Void
• Ord (Proxy a)
• (Ord a) => Ord (Array a)
• Ord Ordering
• (RowToList row list, OrdRecord list row) => Ord (Record row)

class (Semiring a) <= Ring a  where

The Ring class is for types that support addition, multiplication, and subtraction operations.

Instances must satisfy the following laws in addition to the Semiring laws:

• Additive inverse: a - a = zero
• Compatibility of sub and negate: a - b = a + (zero - b)

Members

• sub :: a -> a -> a

Instances

• Ring Int
• Ring Number
• Ring Unit
• (Ring b) => Ring (a -> b)
• Ring (Proxy a)
• (RowToList row list, RingRecord list row row) => Ring (Record row)

class Semigroup a  where

The Semigroup type class identifies an associative operation on a type.

Instances are required to satisfy the following law:

• Associativity: (x <> y) <> z = x <> (y <> z)

One example of a Semigroup is String, with (<>) defined as string concatenation. Another example is List a, with (<>) defined as list concatenation.

Newtypes for Semigroup

There are two other ways to implement an instance for this type class regardless of which type is used. These instances can be used by wrapping the values in one of the two newtypes below:

1. First - Use the first argument every time: append first _ = first.
2. Last - Use the last argument every time: append _ last = last.

Members

• append :: a -> a -> a

Instances

• Semigroup String
• Semigroup Unit
• Semigroup Void
• (Semigroup s') => Semigroup (s -> s')
• Semigroup (Array a)
• Semigroup (Proxy a)
• (RowToList row list, SemigroupRecord list row row) => Semigroup (Record row)

class Semigroupoid :: forall k. (k -> k -> Type) -> Constraintclass Semigroupoid a  where

A Semigroupoid is similar to a Category but does not require an identity element identity, just composable morphisms.

Semigroupoids must satisfy the following law:

• Associativity: p <<< (q <<< r) = (p <<< q) <<< r

One example of a Semigroupoid is the function type constructor (->), with (<<<) defined as function composition.

Members

• compose :: forall b c d. a c d -> a b c -> a b d

Instances

• Semigroupoid Function

class Semiring a  where

The Semiring class is for types that support an addition and multiplication operation.

Instances must satisfy the following laws:

• Commutative monoid under addition:
  • Associativity: (a + b) + c = a + (b + c)
  • Identity: zero + a = a + zero = a
  • Commutative: a + b = b + a
• Monoid under multiplication:
  • Associativity: (a * b) * c = a * (b * c)
  • Identity: one * a = a * one = a
• Multiplication distributes over addition:
  • Left distributivity: a * (b + c) = (a * b) + (a * c)
  • Right distributivity: (a + b) * c = (a * c) + (b * c)
• Annihilation: zero * a = a * zero = zero

Note: The Number and Int types are not fully law abiding members of this class hierarchy due to the potential for arithmetic overflows, and in the case of Number, the presence of NaN and Infinity values. The behaviour is unspecified in these cases.

Members

• add :: a -> a -> a
• zero :: a
• mul :: a -> a -> a
• one :: a

Instances

• Semiring Int
• Semiring Number
• (Semiring b) => Semiring (a -> b)
• Semiring Unit
• Semiring (Proxy a)
• (RowToList row list, SemiringRecord list row row) => Semiring (Record row)

class Show a  where

The Show type class represents those types which can be converted into a human-readable String representation.

While not required, it is recommended that for any expression x, the string show x be executable PureScript code which evaluates to the same value as the expression x.

Members

• show :: a -> String

Instances

• Show Unit
• Show Boolean
• Show Int
• Show Number
• Show Char
• Show String
• (Show a) => Show (Array a)
• Show (Proxy a)
• Show Void
• (Nub rs rs, RowToList rs ls, ShowRecordFields ls rs) => Show (Record rs)

whenM :: forall m. Monad m => m Boolean -> m Unit -> m Unit

Perform a monadic action when a condition is true, where the conditional value is also in a monadic context.

when :: forall m. Applicative m => Boolean -> m Unit -> m Unit

Perform an applicative action when a condition is true.

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)

unlessM :: forall m. Monad m => m Boolean -> m Unit -> m Unit

Perform a monadic action unless a condition is true, where the conditional value is also in a monadic context.

unless :: forall m. Applicative m => Boolean -> m Unit -> m Unit

Perform an applicative action unless a condition is true.

unit :: Unit

unit is the sole inhabitant of the Unit type.

otherwise :: Boolean

An alias for true, which can be useful in guard clauses:

max x y | x >= y    = x
        | otherwise = y

notEq :: forall a. Eq a => a -> a -> Boolean

notEq tests whether one value is not equal to another. Shorthand for not (eq x y).

negate :: forall a. Ring a => a -> a

negate x can be used as a shorthand for zero - x.

min :: forall a. Ord a => a -> a -> a

Take the minimum of two values. If they are considered equal, the first argument is chosen.

max :: forall a. Ord a => a -> a -> a

Take the maximum of two values. If they are considered equal, the first argument is chosen.

liftM1 :: forall m a b. Monad m => (a -> b) -> m a -> m b

liftM1 provides a default implementation of (<$>) for any Monad, without using (<$>) as provided by the Functor-Monad superclass relationship.

liftM1 can therefore be used to write Functor instances as follows:

instance functorF :: Functor F where
  map = liftM1

liftA1 :: forall f a b. Applicative f => (a -> b) -> f a -> f b

liftA1 provides a default implementation of (<$>) for any Applicative functor, without using (<$>) as provided by the Functor-Applicative superclass relationship.

liftA1 can therefore be used to write Functor instances as follows:

instance functorF :: Functor F where
  map = liftA1

lcm :: forall a. Eq a => EuclideanRing a => a -> a -> a

The least common multiple of two values.

join :: forall a m. Bind m => m (m a) -> m a

Collapse two applications of a monadic type constructor into one.

ifM :: forall a m. Bind m => m Boolean -> m a -> m a -> m a

Execute a monadic action if a condition holds.

For example:

main = ifM ((< 0.5) <$> random)
         (trace "Heads")
         (trace "Tails")

gcd :: forall a. Eq a => EuclideanRing a => a -> a -> a

The greatest common divisor of two values.

flip :: forall a b c. (a -> b -> c) -> b -> a -> c

Given a function that takes two arguments, applies the arguments to the function in a swapped order.

flip append "1" "2" == append "2" "1" == "21"

const 1 "two" == 1

flip const 1 "two" == const "two" 1 == "two"

flap :: forall f a b. Functor f => f (a -> b) -> a -> f b

Apply a value in a computational context to a value in no context.

Generalizes flip.

longEnough :: String -> Bool
hasSymbol :: String -> Bool
hasDigit :: String -> Bool
password :: String

validate :: String -> Array Bool
validate = flap [longEnough, hasSymbol, hasDigit]

flap (-) 3 4 == 1
threeve <$> Just 1 <@> 'a' <*> Just true == Just (threeve 1 'a' true)

const :: forall a b. a -> b -> a

Returns its first argument and ignores its second.

const 1 "hello" = 1

It can also be thought of as creating a function that ignores its argument:

const 1 = \_ -> 1

comparing :: forall a b. Ord b => (a -> b) -> (a -> a -> Ordering)

Compares two values by mapping them to a type with an Ord instance.

clamp :: forall a. Ord a => a -> a -> a -> a

Clamp a value between a minimum and a maximum. For example:

let f = clamp 0 10
f (-5) == 0
f 5    == 5
f 15   == 10

between :: forall a. Ord a => a -> a -> a -> Boolean

Test whether a value is between a minimum and a maximum (inclusive). For example:

let f = between 0 10
f 0    == true
f (-5) == false
f 5    == true
f 10   == true
f 15   == false

ap :: forall m a b. Monad m => m (a -> b) -> m a -> m b

ap provides a default implementation of (<*>) for any Monad, without using (<*>) as provided by the Apply-Monad superclass relationship.

ap can therefore be used to write Apply instances as follows:

instance applyF :: Apply F where
  apply = ap

absurd :: forall a. Void -> a

Eliminator for the Void type. Useful for stating that some code branch is impossible because you've "acquired" a value of type Void (which you can't).

rightOnly :: forall t . Either Void t -> t
rightOnly (Left v) = absurd v
rightOnly (Right t) = t

Operator alias for Data.HeytingAlgebra.disj (right-associative / precedence 2)

Operator alias for Control.Semigroupoid.composeFlipped (right-associative / precedence 9)

Operator alias for Control.Bind.bind (left-associative / precedence 1)

Operator alias for Control.Bind.composeKleisli (right-associative / precedence 1)

Operator alias for Data.Ord.greaterThanOrEq (left-associative / precedence 4)

Operator alias for Data.Ord.greaterThan (left-associative / precedence 4)

Operator alias for Data.Eq.eq (non-associative / precedence 4)

Operator alias for Control.Bind.bindFlipped (right-associative / precedence 1)

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

Operator alias for Data.Semigroup.append (right-associative / precedence 5)

Operator alias for Control.Bind.composeKleisliFlipped (right-associative / precedence 1)

Operator alias for Data.Ord.lessThanOrEq (left-associative / precedence 4)

Operator alias for Control.Semigroupoid.compose (right-associative / precedence 9)

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

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

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.Ord.lessThan (left-associative / precedence 4)

Operator alias for Data.Eq.notEq (non-associative / precedence 4)

Operator alias for Data.EuclideanRing.div (left-associative / precedence 7)

Operator alias for Data.Ring.sub (left-associative / precedence 6)

Operator alias for Data.Semiring.add (left-associative / precedence 6)

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

Operator alias for Data.Semiring.mul (left-associative / precedence 7)

Operator alias for Data.HeytingAlgebra.conj (right-associative / precedence 3)

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

Operator alias for Data.Function.apply (right-associative / precedence 0)

Applies a function to an argument: the reverse of (#).

length $ groupBy productCategory $ filter isInStock $ products

is equivalent to:

length (groupBy productCategory (filter isInStock products))

Or another alternative equivalent, applying chain of composed functions to a value:

length <<< groupBy productCategory <<< filter isInStock $ products

Operator alias for Data.Function.applyFlipped (left-associative / precedence 1)

Applies an argument to a function: the reverse of ($).

products # filter isInStock # groupBy productCategory # length

is equivalent to:

length (groupBy productCategory (filter isInStock products))

Or another alternative equivalent, applying a value to a chain of composed functions:

products # filter isInStock >>> groupBy productCategory >>> length

Operator alias for Data.NaturalTransformation.NaturalTransformation (right-associative / precedence 4)

Operator alias for Type.Row.RowApply (right-associative / precedence 0)

Applies a type alias of open rows to a set of rows. The primary use case this operator is as convenient sugar for combining open rows without parentheses.

type Rows1 r = (a :: Int, b :: String | r)
type Rows2 r = (c :: Boolean | r)
type Rows3 r = (Rows1 + Rows2 + r)
type Rows4 r = (d :: String | Rows1 + Rows2 + r)