MasonPrelude
- Package
- purescript-mason-prelude
- Repository
- ursi/purescript-mason-prelude
Re-exports from Control.Alt
#Alt Source
class Alt :: (Type -> Type) -> Constraint
class (Functor f) <= Alt f
The Alt
type class identifies an associative operation on a type
constructor. It is similar to Semigroup
, except that it applies to
types of kind * -> *
, like Array
or List
, rather than concrete types
String
or Number
.
Alt
instances are required to satisfy the following laws:
- Associativity:
(x <|> y) <|> z == x <|> (y <|> z)
- Distributivity:
f <$> (x <|> y) == (f <$> x) <|> (f <$> y)
For example, the Array
([]
) type is an instance of Alt
, where
(<|>)
is defined to be concatenation.
A common use case is to select the first "valid" item, or, if all items are "invalid", the last "invalid" item.
For example:
import Control.Alt ((<|>))
import Data.Maybe (Maybe(..)
import Data.Either (Either(..))
Nothing <|> Just 1 <|> Just 2 == Just 1
Left "err" <|> Right 1 <|> Right 2 == Right 1
Left "err 1" <|> Left "err 2" <|> Left "err 3" == Left "err 3"
Instances
Re-exports from Control.Apply
Re-exports from Control.Parallel
#parTraverse_ Source
parTraverse_ :: forall f m t a b. Parallel f m => Foldable t => (a -> m b) -> t a -> m Unit
Traverse a collection in parallel, discarding any results.
#parTraverse Source
parTraverse :: forall f m t a b. Parallel f m => Traversable t => (a -> m b) -> t a -> m (t b)
Traverse a collection in parallel.
#parSequence Source
parSequence :: forall a t m f. Parallel f m => Traversable t => t (m a) -> m (t a)
#parOneOfMap Source
parOneOfMap :: forall a b t m f. Parallel f m => Alternative f => Foldable t => Functor t => (a -> m b) -> t a -> m b
Race a collection in parallel while mapping to some effect.
#parOneOf Source
parOneOf :: forall a t m f. Parallel f m => Alternative f => Foldable t => Functor t => t (m a) -> m a
Race a collection in parallel.
Re-exports from Data.Either
#Either Source
data Either a b
The Either
type is used to represent a choice between two types of value.
A common use case for Either
is error handling, where Left
is used to
carry an error value and Right
is used to carry a success value.
Constructors
Instances
Functor (Either a)
Generic (Either a b) _
Invariant (Either a)
Apply (Either e)
The
Apply
instance allows functions contained within aRight
to transform a value contained within aRight
using the(<*>)
operator:Right f <*> Right x == Right (f x)
Left
values are left untouched:Left f <*> Right x == Left f Right f <*> Left y == Left y
Combining
Functor
's<$>
withApply
's<*>
can be used to transform a pure function to takeEither
-typed arguments sof :: a -> b -> c
becomesf :: Either l a -> Either l b -> Either l c
:f <$> Right x <*> Right y == Right (f x y)
The
Left
-preserving behaviour of both operators means the result of an expression like the above but where any one of the values isLeft
means the whole result becomesLeft
also, taking the firstLeft
value found:f <$> 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 intoEither
with thepure
function:pure x :: Either _ _ == Right x
Combining
Functor
's<$>
withApply
's<*>
andApplicative
'spure
can be used to pass a mixture ofEither
and non-Either
typed values to a function that does not usually expect them, by usingpure
for any value that is not alreadyEither
typed:f <$> Right x <*> pure y == Right (f x y)
Even though
pure = Right
it is recommended to usepure
in situations like this as it allows the choice ofApplicative
to be changed later without having to go through and replaceRight
with a new constructor.Alt (Either e)
The
Alt
instance allows for a choice to be made between twoEither
values with the<|>
operator, where the firstRight
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 ofEither
values and functions that return anEither
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 bothApplicative
andBind
instances forEither
.Extend (Either e)
The
Extend
instance allows sequencing ofEither
values and functions that accept anEither
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 allowsEither
values to be rendered as a string withshow
whenever there is anShow
instance for both type theEither
can contain.(Eq a, Eq b) => Eq (Either a b)
The
Eq
instance allowsEither
values to be checked for equality with==
and inequality with/=
whenever there is anEq
instance for both types theEither
can contain.(Eq a) => Eq1 (Either a)
(Ord a, Ord b) => Ord (Either a b)
The
Ord
instance allowsEither
values to be compared withcompare
,>
,>=
,<
and<=
whenever there is anOrd
instance for both types theEither
can contain.Any
Left
value is considered to be less than aRight
value.(Ord a) => Ord1 (Either a)
(Bounded a, Bounded b) => Bounded (Either a b)
(Semigroup b) => Semigroup (Either a b)
Re-exports from Data.Either.Nested
Re-exports from Data.Foldable
#Foldable Source
class Foldable :: (Type -> Type) -> Constraint
class Foldable f where
Foldable
represents data structures which can be folded.
foldr
folds a structure from the rightfoldl
folds a structure from the leftfoldMap
folds a structure by accumulating values in aMonoid
Default implementations are provided by the following functions:
foldrDefault
foldlDefault
foldMapDefaultR
foldMapDefaultL
Note: some combinations of the default implementations are unsafe to use together - causing a non-terminating mutually recursive cycle. These combinations are documented per function.
Members
foldr :: forall a b. (a -> b -> b) -> b -> f a -> b
foldl :: forall a b. (b -> a -> b) -> b -> f a -> b
foldMap :: forall a m. Monoid m => (a -> m) -> f a -> m
Instances
Foldable Array
Foldable Maybe
Foldable First
Foldable Last
Foldable Additive
Foldable Dual
Foldable Disj
Foldable Conj
Foldable Multiplicative
Foldable (Either a)
Foldable (Tuple a)
Foldable Identity
Foldable (Const a)
(Foldable f, Foldable g) => Foldable (Product f g)
(Foldable f, Foldable g) => Foldable (Coproduct f g)
(Foldable f, Foldable g) => Foldable (Compose f g)
(Foldable f) => Foldable (App f)
#traverse_ Source
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_ Source
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 Source
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]
Re-exports from Data.FoldableWithIndex
#FoldableWithIndex Source
class FoldableWithIndex :: Type -> (Type -> Type) -> Constraint
class (Foldable f) <= FoldableWithIndex i f | f -> i where
A Foldable
with an additional index.
A FoldableWithIndex
instance must be compatible with its Foldable
instance
foldr f = foldrWithIndex (const f)
foldl f = foldlWithIndex (const f)
foldMap f = foldMapWithIndex (const f)
Default implementations are provided by the following functions:
foldrWithIndexDefault
foldlWithIndexDefault
foldMapWithIndexDefaultR
foldMapWithIndexDefaultL
Note: some combinations of the default implementations are unsafe to use together - causing a non-terminating mutually recursive cycle. These combinations are documented per function.
Members
foldrWithIndex :: forall a b. (i -> a -> b -> b) -> b -> f a -> b
foldlWithIndex :: forall a b. (i -> b -> a -> b) -> b -> f a -> b
foldMapWithIndex :: forall a m. Monoid m => (i -> a -> m) -> f a -> m
Instances
FoldableWithIndex Int Array
FoldableWithIndex Unit Maybe
FoldableWithIndex Unit First
FoldableWithIndex Unit Last
FoldableWithIndex Unit Additive
FoldableWithIndex Unit Dual
FoldableWithIndex Unit Disj
FoldableWithIndex Unit Conj
FoldableWithIndex Unit Multiplicative
FoldableWithIndex Unit (Either a)
FoldableWithIndex Unit (Tuple a)
FoldableWithIndex Unit Identity
FoldableWithIndex Void (Const a)
(FoldableWithIndex a f, FoldableWithIndex b g) => FoldableWithIndex (Either a b) (Product f g)
(FoldableWithIndex a f, FoldableWithIndex b g) => FoldableWithIndex (Either a b) (Coproduct f g)
(FoldableWithIndex a f, FoldableWithIndex b g) => FoldableWithIndex (Tuple a b) (Compose f g)
(FoldableWithIndex a f) => FoldableWithIndex a (App f)
Re-exports from Data.Function.Uncurried
Re-exports from Data.FunctorWithIndex
#FunctorWithIndex Source
class FunctorWithIndex :: Type -> (Type -> Type) -> Constraint
class (Functor f) <= FunctorWithIndex i f | f -> i where
A Functor
with an additional index.
Instances must satisfy a modified form of the Functor
laws
mapWithIndex (\_ a -> a) = identity
mapWithIndex f . mapWithIndex g = mapWithIndex (\i -> f i <<< g i)
and be compatible with the Functor
instance
map f = mapWithIndex (const f)
Members
mapWithIndex :: forall a b. (i -> a -> b) -> f a -> f b
Instances
FunctorWithIndex Int Array
FunctorWithIndex Unit Maybe
FunctorWithIndex Unit First
FunctorWithIndex Unit Last
FunctorWithIndex Unit Additive
FunctorWithIndex Unit Dual
FunctorWithIndex Unit Conj
FunctorWithIndex Unit Disj
FunctorWithIndex Unit Multiplicative
FunctorWithIndex Unit (Either a)
FunctorWithIndex Unit (Tuple a)
FunctorWithIndex Unit Identity
FunctorWithIndex Void (Const a)
(FunctorWithIndex a f, FunctorWithIndex b g) => FunctorWithIndex (Either a b) (Product f g)
(FunctorWithIndex a f, FunctorWithIndex b g) => FunctorWithIndex (Either a b) (Coproduct f g)
(FunctorWithIndex a f, FunctorWithIndex b g) => FunctorWithIndex (Tuple a b) (Compose f g)
(FunctorWithIndex a f) => FunctorWithIndex a (App f)
Re-exports from Data.Generic.Rep
#Generic Source
class Generic a rep | a -> rep
The Generic
class asserts the existence of a type function from types
to their representations using the type constructors defined in this module.
Re-exports from Data.Int
Re-exports from Data.List
#List Source
data List a
Constructors
Instances
(Show a) => Show (List a)
(Eq a) => Eq (List a)
Eq1 List
(Ord a) => Ord (List a)
Ord1 List
Semigroup (List a)
Monoid (List a)
Functor List
FunctorWithIndex Int List
Foldable List
FoldableWithIndex Int List
Unfoldable1 List
Unfoldable List
Traversable List
TraversableWithIndex Int List
Apply List
Applicative List
Bind List
Monad List
Alt List
Plus List
Alternative List
MonadPlus List
Extend List
Re-exports from Data.Maybe
#Maybe Source
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
Instances
Functor Maybe
The
Functor
instance allows functions to transform the contents of aJust
with the<$>
operator:f <$> Just x == Just (f x)
Nothing
values are left untouched:f <$> Nothing == Nothing
Apply Maybe
The
Apply
instance allows functions contained within aJust
to transform a value contained within aJust
using theapply
operator:Just f <*> Just x == Just (f x)
Nothing
values are left untouched:Just f <*> Nothing == Nothing Nothing <*> Just x == Nothing
Combining
Functor
's<$>
withApply
's<*>
can be used transform a pure function to takeMaybe
-typed arguments sof :: a -> b -> c
becomesf :: Maybe a -> Maybe b -> Maybe c
:f <$> Just x <*> Just y == Just (f x y)
The
Nothing
-preserving behaviour of both operators means the result of an expression like the above but where any one of the values isNothing
means the whole result becomesNothing
also:f <$> Nothing <*> Just y == Nothing f <$> Just x <*> Nothing == Nothing f <$> Nothing <*> Nothing == Nothing
Applicative Maybe
The
Applicative
instance enables lifting of values intoMaybe
with thepure
function:pure x :: Maybe _ == Just x
Combining
Functor
's<$>
withApply
's<*>
andApplicative
'spure
can be used to pass a mixture ofMaybe
and non-Maybe
typed values to a function that does not usually expect them, by usingpure
for any value that is not alreadyMaybe
typed:f <$> Just x <*> pure y == Just (f x y)
Even though
pure = Just
it is recommended to usepure
in situations like this as it allows the choice ofApplicative
to be changed later without having to go through and replaceJust
with a new constructor.Alt Maybe
The
Alt
instance allows for a choice to be made between twoMaybe
values with the<|>
operator, where the firstJust
encountered is taken.Just x <|> Just y == Just x Nothing <|> Just y == Just y Nothing <|> Nothing == Nothing
Plus Maybe
The
Plus
instance provides a defaultMaybe
value:empty :: Maybe _ == Nothing
Alternative Maybe
The
Alternative
instance guarantees that there are bothApplicative
andPlus
instances forMaybe
.Bind Maybe
The
Bind
instance allows sequencing ofMaybe
values and functions that return aMaybe
by using the>>=
operator:Just x >>= f = f x Nothing >>= f = Nothing
Monad Maybe
The
Monad
instance guarantees that there are bothApplicative
andBind
instances forMaybe
. This also enables thedo
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 ofMaybe
values and functions that accept aMaybe 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<>
onMaybe
values whenever there is aSemigroup
instance for the type theMaybe
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 allowsMaybe
values to be checked for equality with==
and inequality with/=
whenever there is anEq
instance for the type theMaybe
contains.Eq1 Maybe
(Ord a) => Ord (Maybe a)
The
Ord
instance allowsMaybe
values to be compared withcompare
,>
,>=
,<
and<=
whenever there is anOrd
instance for the type theMaybe
contains.Nothing
is considered to be less than anyJust
value.Ord1 Maybe
(Bounded a) => Bounded (Maybe a)
(Show a) => Show (Maybe a)
The
Show
instance allowsMaybe
values to be rendered as a string withshow
whenever there is anShow
instance for the type theMaybe
contains.Generic (Maybe a) _
#maybe Source
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
Re-exports from Data.Show.Generic
#genericShow Source
genericShow :: forall a rep. Generic a rep => GenericShow rep => a -> String
A Generic
implementation of the show
member from the Show
type class.
Re-exports from Data.String
Re-exports from Data.String.CodeUnits
#toCharArray Source
toCharArray :: String -> Array Char
Converts the string into an array of characters.
toCharArray "Hello☺\n" == ['H','e','l','l','o','☺','\n']
#fromCharArray Source
fromCharArray :: Array Char -> String
Converts an array of characters into a string.
fromCharArray ['H', 'e', 'l', 'l', 'o'] == "Hello"
Re-exports from Data.Traversable
#Traversable Source
class Traversable :: (Type -> Type) -> Constraint
class (Functor t, Foldable t) <= Traversable t where
Traversable
represents data structures which can be traversed,
accumulating results and effects in some Applicative
functor.
traverse
runs an action for every element in a data structure, and accumulates the results.sequence
runs the actions contained in a data structure, and accumulates the results.
import Data.Traversable
import Data.Maybe
import Data.Int (fromNumber)
sequence [Just 1, Just 2, Just 3] == Just [1,2,3]
sequence [Nothing, Just 2, Just 3] == Nothing
traverse fromNumber [1.0, 2.0, 3.0] == Just [1,2,3]
traverse fromNumber [1.5, 2.0, 3.0] == Nothing
traverse logShow [1,2,3]
-- prints:
1
2
3
traverse (\x -> [x, 0]) [1,2,3] == [[1,2,3],[1,2,0],[1,0,3],[1,0,0],[0,2,3],[0,2,0],[0,0,3],[0,0,0]]
The traverse
and sequence
functions should be compatible in the
following sense:
traverse f xs = sequence (f <$> xs)
sequence = traverse identity
Traversable
instances should also be compatible with the corresponding
Foldable
instances, in the following sense:
foldMap f = runConst <<< traverse (Const <<< f)
Default implementations are provided by the following functions:
traverseDefault
sequenceDefault
Members
traverse :: forall a b m. Applicative m => (a -> m b) -> t a -> m (t b)
sequence :: forall a m. Applicative m => t (m a) -> m (t a)
Instances
Traversable Array
Traversable Maybe
Traversable First
Traversable Last
Traversable Additive
Traversable Dual
Traversable Conj
Traversable Disj
Traversable Multiplicative
Traversable (Either a)
Traversable (Tuple a)
Traversable Identity
Traversable (Const a)
(Traversable f, Traversable g) => Traversable (Product f g)
(Traversable f, Traversable g) => Traversable (Coproduct f g)
(Traversable f, Traversable g) => Traversable (Compose f g)
(Traversable f) => Traversable (App f)
Re-exports from Data.TraversableWithIndex
#TraversableWithIndex Source
class TraversableWithIndex :: Type -> (Type -> Type) -> Constraint
class (FunctorWithIndex i t, FoldableWithIndex i t, Traversable t) <= TraversableWithIndex i t | t -> i where
A Traversable
with an additional index.
A TraversableWithIndex
instance must be compatible with its
Traversable
instance
traverse f = traverseWithIndex (const f)
with its FoldableWithIndex
instance
foldMapWithIndex f = unwrap <<< traverseWithIndex (\i -> Const <<< f i)
and with its FunctorWithIndex
instance
mapWithIndex f = unwrap <<< traverseWithIndex (\i -> Identity <<< f i)
A default implementation is provided by traverseWithIndexDefault
.
Members
traverseWithIndex :: forall a b m. Applicative m => (i -> a -> m b) -> t a -> m (t b)
Instances
TraversableWithIndex Int Array
TraversableWithIndex Unit Maybe
TraversableWithIndex Unit First
TraversableWithIndex Unit Last
TraversableWithIndex Unit Additive
TraversableWithIndex Unit Dual
TraversableWithIndex Unit Conj
TraversableWithIndex Unit Disj
TraversableWithIndex Unit Multiplicative
TraversableWithIndex Unit (Either a)
TraversableWithIndex Unit (Tuple a)
TraversableWithIndex Unit Identity
TraversableWithIndex Void (Const a)
(TraversableWithIndex a f, TraversableWithIndex b g) => TraversableWithIndex (Either a b) (Product f g)
(TraversableWithIndex a f, TraversableWithIndex b g) => TraversableWithIndex (Either a b) (Coproduct f g)
(TraversableWithIndex a f, TraversableWithIndex b g) => TraversableWithIndex (Tuple a b) (Compose f g)
(TraversableWithIndex a f) => TraversableWithIndex a (App f)
Re-exports from Data.Tuple
#Tuple Source
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
Tuple
s to be rendered as a string withshow
whenever there areShow
instances for both component types.(Eq a, Eq b) => Eq (Tuple a b)
Allows
Tuple
s to be checked for equality with==
and/=
whenever there areEq
instances for both component types.(Eq a) => Eq1 (Tuple a)
(Ord a, Ord b) => Ord (Tuple a b)
Allows
Tuple
s to be compared withcompare
,>
,>=
,<
and<=
whenever there areOrd
instances for both component types. To obtain the result, thefst
s arecompare
d, and if they areEQ
ual, thesnd
s arecompare
d.(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<>
onTuple
s whenever there areSemigroup
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 aTuple
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 aTuple
with the<*>
operator whenever there is aSemigroup
instance for thefst
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)
Re-exports from Data.Tuple.Nested
#(/\) Source
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)))
#type (/\) Source
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)))
Re-exports from Data.Unfoldable
#Unfoldable Source
class Unfoldable :: (Type -> Type) -> Constraint
class (Unfoldable1 t) <= Unfoldable t where
This class identifies (possibly empty) data structures which can be unfolded.
The generating function f
in unfoldr f
is understood as follows:
- If
f b
isNothing
, thenunfoldr f b
should be empty. - If
f b
isJust (Tuple a b1)
, thenunfoldr f b
should consist ofa
appended to the result ofunfoldr f b1
.
Note that it is not possible to give Unfoldable
instances to types which
represent structures which are guaranteed to be non-empty, such as
NonEmptyArray
: consider what unfoldr (const Nothing)
should produce.
Structures which are guaranteed to be non-empty can instead be given
Unfoldable1
instances.
Members
Instances
Re-exports from Debug
#todo Source
todo :: forall a. a
A placeholder to use when you want your code to compile without finishing something. You will immediately get an error when trying to run any code with a todo
, so you won't forget about it and run into errors later.
#debugger Source
debugger :: forall a. a -> a
Inserts a JavaScript debugger
statement, then returns its argument.
Re-exports from Effect
#Effect Source
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'sSemigroup
instance.(Monoid a) => Monoid (Effect a)
If you have a
Monoid a
instance, thenmempty :: Effect a
is defined aspure mempty
.
Re-exports from Effect.Class
#MonadEffect Source
class MonadEffect :: (Type -> Type) -> Constraint
class (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
Re-exports from Effect.Class.Console
Re-exports from Effect.Exception
Re-exports from Effect.Exception.Unsafe
#unsafeThrow Source
unsafeThrow :: forall a. String -> a
Defined as unsafeThrowException <<< error
.
Re-exports from Effect.Uncurried
#EffectFn10 Source
data EffectFn10 t0 t1 t2 t3 t4 t5 t6 t7 t8 t9 t10
Instances
(Semigroup r) => Semigroup (EffectFn10 a b c d e f g h i j r)
(Monoid r) => Monoid (EffectFn10 a b c d e f g h i j r)
#runEffectFn9 Source
runEffectFn9 :: forall a b c d e f g h i r. EffectFn9 a b c d e f g h i r -> a -> b -> c -> d -> e -> f -> g -> h -> i -> Effect r
#runEffectFn8 Source
runEffectFn8 :: forall a b c d e f g h r. EffectFn8 a b c d e f g h r -> a -> b -> c -> d -> e -> f -> g -> h -> Effect r
#runEffectFn7 Source
runEffectFn7 :: forall a b c d e f g r. EffectFn7 a b c d e f g r -> a -> b -> c -> d -> e -> f -> g -> Effect r
#runEffectFn6 Source
runEffectFn6 :: forall a b c d e f r. EffectFn6 a b c d e f r -> a -> b -> c -> d -> e -> f -> Effect r
#runEffectFn5 Source
runEffectFn5 :: forall a b c d e r. EffectFn5 a b c d e r -> a -> b -> c -> d -> e -> Effect r
#runEffectFn4 Source
runEffectFn4 :: forall a b c d r. EffectFn4 a b c d r -> a -> b -> c -> d -> Effect r
#runEffectFn3 Source
runEffectFn3 :: forall a b c r. EffectFn3 a b c r -> a -> b -> c -> Effect r
#runEffectFn2 Source
runEffectFn2 :: forall a b r. EffectFn2 a b r -> a -> b -> Effect r
#runEffectFn10 Source
runEffectFn10 :: forall a b c d e f g h i j r. EffectFn10 a b c d e f g h i j r -> a -> b -> c -> d -> e -> f -> g -> h -> i -> j -> Effect r
#runEffectFn1 Source
runEffectFn1 :: forall a r. EffectFn1 a r -> a -> Effect r
#mkEffectFn9 Source
mkEffectFn9 :: forall a b c d e f g h i r. (a -> b -> c -> d -> e -> f -> g -> h -> i -> Effect r) -> EffectFn9 a b c d e f g h i r
#mkEffectFn8 Source
mkEffectFn8 :: forall a b c d e f g h r. (a -> b -> c -> d -> e -> f -> g -> h -> Effect r) -> EffectFn8 a b c d e f g h r
#mkEffectFn7 Source
mkEffectFn7 :: forall a b c d e f g r. (a -> b -> c -> d -> e -> f -> g -> Effect r) -> EffectFn7 a b c d e f g r
#mkEffectFn6 Source
mkEffectFn6 :: forall a b c d e f r. (a -> b -> c -> d -> e -> f -> Effect r) -> EffectFn6 a b c d e f r
#mkEffectFn5 Source
mkEffectFn5 :: forall a b c d e r. (a -> b -> c -> d -> e -> Effect r) -> EffectFn5 a b c d e r
#mkEffectFn4 Source
mkEffectFn4 :: forall a b c d r. (a -> b -> c -> d -> Effect r) -> EffectFn4 a b c d r
#mkEffectFn3 Source
mkEffectFn3 :: forall a b c r. (a -> b -> c -> Effect r) -> EffectFn3 a b c r
#mkEffectFn2 Source
mkEffectFn2 :: forall a b r. (a -> b -> Effect r) -> EffectFn2 a b r
#mkEffectFn10 Source
mkEffectFn10 :: forall a b c d e f g h i j r. (a -> b -> c -> d -> e -> f -> g -> h -> i -> j -> Effect r) -> EffectFn10 a b c d e f g h i j r
#mkEffectFn1 Source
mkEffectFn1 :: forall a r. (a -> Effect r) -> EffectFn1 a r
Re-exports from Effect.Unsafe
#unsafePerformEffect Source
unsafePerformEffect :: forall a. Effect a -> a
Run an effectful computation.
Note: use of this function can result in arbitrary side-effects.
Re-exports from MasonPrelude.Functor.Nested
#mmmapFlipped Source
mmmapFlipped :: forall a b f g h. Functor f => Functor g => Functor h => f (g (h a)) -> (a -> b) -> f (g (h b))
#mmapFlipped Source
mmapFlipped :: forall a b f g. Functor f => Functor g => f (g a) -> (a -> b) -> f (g b)
#(<$$$>) Source
Operator alias for MasonPrelude.Functor.Nested.mmap (left-associative / precedence 4)
#(<##>) Source
Operator alias for MasonPrelude.Functor.Nested.mmapFlipped (left-associative / precedence 1)
#(<###>) Source
Operator alias for MasonPrelude.Functor.Nested.mmmapFlipped (left-associative / precedence 1)
Re-exports from MasonPrelude.Parallel
Re-exports from PointFree
#composeThirdFlipped Source
composeThirdFlipped :: forall a b x y z. (z -> b) -> (x -> y -> b -> a) -> x -> y -> z -> a
#composeThird Source
composeThird :: forall a b x y z. (x -> y -> b -> a) -> (z -> b) -> x -> y -> z -> a
\f g x y z -> f x y (g z)
#composeSecondFlipped Source
composeSecondFlipped :: forall a b x y. (y -> b) -> (x -> b -> a) -> x -> y -> a
#composeSecond Source
composeSecond :: forall a b x y. (x -> b -> a) -> (y -> b) -> x -> y -> a
\f g x y -> f x (g y)
#composeFourthFlipped Source
composeFourthFlipped :: forall a b w x y z. (z -> b) -> (w -> x -> y -> b -> a) -> w -> x -> y -> z -> a
#composeFourth Source
composeFourth :: forall a b w x y z. (w -> x -> y -> b -> a) -> (z -> b) -> w -> x -> y -> z -> a
\f g w x y z -> f w x y (g z)
#compose4Flipped Source
compose4Flipped :: forall a b w x y z. (w -> x -> y -> z -> a) -> (a -> b) -> w -> x -> y -> z -> b
#compose4 Source
compose4 :: forall a b w x y z. (a -> b) -> (w -> x -> y -> z -> a) -> w -> x -> y -> z -> b
\f g w x y z -> f (g w x y z)
#compose3SecondFlipped Source
compose3SecondFlipped :: forall a b w x y z. (x -> y -> z -> b) -> (w -> b -> a) -> w -> x -> y -> z -> a
#compose3Second Source
compose3Second :: forall a b w x y z. (w -> b -> a) -> (x -> y -> z -> b) -> w -> x -> y -> z -> a
\f g w x y z -> f w (g x y z)
#compose3Flipped Source
compose3Flipped :: forall a b x y z. (x -> y -> z -> a) -> (a -> b) -> x -> y -> z -> b
#compose3 Source
compose3 :: forall a b x y z. (a -> b) -> (x -> y -> z -> a) -> x -> y -> z -> b
\f g x y z -> f (g x y z)
#compose2ThirdFlipped Source
compose2ThirdFlipped :: forall a b w x y z. (y -> z -> b) -> (w -> x -> b -> a) -> w -> x -> y -> z -> a
#compose2Third Source
compose2Third :: forall a b w x y z. (w -> x -> b -> a) -> (y -> z -> b) -> w -> x -> y -> z -> a
\f g w x y z -> f w x (g y z)
#compose2SecondFlipped Source
compose2SecondFlipped :: forall a b x y z. (y -> z -> b) -> (x -> b -> a) -> x -> y -> z -> a
#compose2Second Source
compose2Second :: forall a b x y z. (x -> b -> a) -> (y -> z -> b) -> x -> y -> z -> a
\f g x y z -> f x (g y z)
#compose2Flipped Source
compose2Flipped :: forall a b x y. (x -> y -> a) -> (a -> b) -> x -> y -> b
#compose2 Source
compose2 :: forall a b x y. (a -> b) -> (x -> y -> a) -> x -> y -> b
\f g x y -> f (g x y)
#applyThirdFlipped Source
applyThirdFlipped :: forall x y z a. x -> (y -> z -> x -> a) -> y -> z -> a
#applyThird Source
applyThird :: forall x y z a. (y -> z -> x -> a) -> x -> y -> z -> a
\f x y z -> f y z x
#applySecondFlipped Source
applySecondFlipped :: forall x y a. x -> (y -> x -> a) -> y -> a
#applyFourthFlipped Source
applyFourthFlipped :: forall w x y z a. w -> (x -> y -> z -> w -> a) -> x -> y -> z -> a
#applyFourth Source
applyFourth :: forall w x y z a. (x -> y -> z -> w -> a) -> w -> x -> y -> z -> a
\f w x y z -> f x y z w
#(<.) Source
Operator alias for Control.Semigroupoid.compose (left-associative / precedence 9)
\f g x -> f (g x)
#(.>) Source
Operator alias for Control.Semigroupoid.composeFlipped (right-associative / precedence 9)
Re-exports from Prelude
#Void Source
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.
Instances
#Unit Source
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.
Instances
#Ordering Source
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
Instances
#Applicative Source
class Applicative :: (Type -> Type) -> Constraint
class (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
#Apply Source
class Apply :: (Type -> Type) -> Constraint
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 ($)
to arguments wrapped with the
type constructor f
.
Put differently...
foo =
functionTakingNArguments <$> 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
#Bind Source
class Bind :: (Type -> Type) -> Constraint
class (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 forArray
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. Eachbind
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
#BooleanAlgebra Source
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)
#Bounded Source
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
Instances
Bounded Boolean
Bounded Int
The
Bounded
Int
instance hastop :: Int
equal to 2^31 - 1, andbottom :: 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)
#Category Source
class Category :: forall k. (k -> k -> Type) -> Constraint
class (Semigroupoid a) <= Category a where
Category
s 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
#CommutativeRing Source
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)
#DivisionRing Source
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-zeroa
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
#Eq Source
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
andy == z
thenx == 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
Instances
#EuclideanRing Source
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 ifa
andb
are both nonzero then so is their producta * b
- Euclidean function
degree
:- Nonnegativity: For all nonzero
a
,degree a >= 0
- Quotient/remainder: For all
a
andb
, whereb
is nonzero, letq = a / b
andr = a `mod` b
; thena = q*b + r
, and also eitherr = zero
ordegree r < degree b
- Nonnegativity: For all nonzero
- Submultiplicative euclidean function:
- For all nonzero
a
andb
,degree a <= degree (a * b)
- For all nonzero
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
Instances
#Field Source
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
#Functor Source
class Functor :: (Type -> Type) -> Constraint
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
#HeytingAlgebra Source
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
Instances
HeytingAlgebra Boolean
HeytingAlgebra Unit
(HeytingAlgebra b) => HeytingAlgebra (a -> b)
HeytingAlgebra (Proxy a)
(RowToList row list, HeytingAlgebraRecord list row row) => HeytingAlgebra (Record row)
#Monad Source
class Monad :: (Type -> Type) -> Constraint
class (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
#Monoid Source
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
Monoid
s 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
<>
could be+
andmempty
could be0
<>
could be*
andmempty
could be1
.
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
#Ord Source
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
andb <= a
thena = b
- Transitivity: if
a <= b
andb <= c
thena <= 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
Instances
#Ring Source
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
andnegate
:a - b = a + (zero - b)
Members
sub :: a -> a -> a
Instances
#Semigroup Source
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:
First
- Use the first argument every time:append first _ = first
.Last
- Use the last argument every time:append _ last = last
.
Members
append :: a -> a -> a
Instances
#Semigroupoid Source
class Semigroupoid :: forall k. (k -> k -> Type) -> Constraint
class Semigroupoid a where
A Semigroupoid
is similar to a Category
but does not
require an identity element identity
, just composable morphisms.
Semigroupoid
s 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
#Semiring Source
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
- Associativity:
- Monoid under multiplication:
- Associativity:
(a * b) * c = a * (b * c)
- Identity:
one * a = a * one = a
- Associativity:
- Multiplication distributes over addition:
- Left distributivity:
a * (b + c) = (a * b) + (a * c)
- Right distributivity:
(a + b) * c = (a * c) + (b * c)
- Left distributivity:
- 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
Instances
#Show Source
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
Instances
#when Source
when :: forall m. Applicative m => Boolean -> m Unit -> m Unit
Perform an applicative action when a condition is true.
#void Source
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)
#unless Source
unless :: forall m. Applicative m => Boolean -> m Unit -> m Unit
Perform an applicative action unless a condition is true.
#liftM1 Source
liftM1 :: forall m a b. Monad m => (a -> b) -> m a -> m b
liftM1
provides a default implementation of (<$>)
for any
Monad
, without using (<$>)
as provided by the
Functor
-Monad
superclass relationship.
liftM1
can therefore be used to write Functor
instances
as follows:
instance functorF :: Functor F where
map = liftM1
#liftA1 Source
liftA1 :: forall f a b. Applicative f => (a -> b) -> f a -> f b
liftA1
provides a default implementation of (<$>)
for any
Applicative
functor, without using (<$>)
as provided
by the Functor
-Applicative
superclass
relationship.
liftA1
can therefore be used to write Functor
instances
as follows:
instance functorF :: Functor F where
map = liftA1
#lcm Source
lcm :: forall a. Eq a => EuclideanRing a => a -> a -> a
The least common multiple of two values.
#gcd Source
gcd :: forall a. Eq a => EuclideanRing a => a -> a -> a
The greatest common divisor of two values.
#flip Source
flip :: forall a b c. (a -> b -> c) -> b -> a -> c
Given a function that takes two arguments, applies the arguments to the function in a swapped order.
flip append "1" "2" == append "2" "1" == "21"
const 1 "two" == 1
flip const 1 "two" == const "two" 1 == "two"
#flap Source
flap :: forall f a b. Functor f => f (a -> b) -> a -> f b
Apply a value in a computational context to a value in no context.
Generalizes flip
.
longEnough :: String -> Bool
hasSymbol :: String -> Bool
hasDigit :: String -> Bool
password :: String
validate :: String -> Array Bool
validate = flap [longEnough, hasSymbol, hasDigit]
flap (-) 3 4 == 1
threeve <$> Just 1 <@> 'a' <*> Just true == Just (threeve 1 'a' true)
#const Source
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
#(>>>) Source
Operator alias for Control.Semigroupoid.composeFlipped (right-associative / precedence 9)
#(<=<) Source
Operator alias for Control.Bind.composeKleisliFlipped (right-associative / precedence 1)
#($) Source
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
#(#) Source
Operator alias for Data.Function.applyFlipped (left-associative / precedence 1)
Applies an argument to a function: the reverse of ($)
.
products # filter isInStock # groupBy productCategory # length
is equivalent to:
length (groupBy productCategory (filter isInStock products))
Or another alternative equivalent, applying a value to a chain of composed functions:
products # filter isInStock >>> groupBy productCategory >>> length
#type (~>) Source
Operator alias for Data.NaturalTransformation.NaturalTransformation (right-associative / precedence 4)
Re-exports from Type.Proxy
Re-exports from Unsafe.Coerce
#unsafeCoerce Source
unsafeCoerce :: forall a b. a -> b
A highly unsafe function, which can be used to persuade the type system that any type is the same as any other type. When using this function, it is your (that is, the caller's) responsibility to ensure that the underlying representation for both types is the same.
Because this function is extraordinarily flexible, type inference can greatly suffer. It is highly recommended to define specializations of this function rather than using it as-is. For example:
fromBoolean :: Boolean -> Json
fromBoolean = unsafeCoerce
This way, you won't have any nasty surprises due to the inferred type being different to what you expected.
After the v0.14.0 PureScript release, some of what was accomplished via
unsafeCoerce
can now be accomplished via coerce
from
purescript-safe-coerce
. See that library's documentation for more
context.
The
Functor
instance allows functions to transform the contents of aRight
with the<$>
operator:Left
values are untouched: