Module

Data.Functor.Variant

Package
purescript-variant
Repository
natefaubion/purescript-variant

#VariantF Source

data VariantF (f :: # Type) a

Instances

#inj Source

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

Inject into the variant at a given label.

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

#prj Source

prj :: forall sym f a r1 r2 g. Cons sym (FProxy f) r1 r2 => Alternative g => IsSymbol sym => SProxy sym -> VariantF r2 a -> g (f a)

Attempt to read a variant at a given label.

case prj (SProxy :: SProxy "foo") maybeAtFoo of
  Just (Just i) -> i + 1
  _ -> 0

#on Source

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

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

#onMatch Source

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

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

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

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

#case_ Source

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

Combinator for exhaustive pattern matching.

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

#match Source

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

Combinator for exhaustive pattern matching using an onMatch case record.

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

#default Source

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

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

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

#expand Source

expand :: forall lt mix gt a. Union lt mix gt => VariantF lt a -> VariantF gt a

Every VariantF lt a can be cast to some VariantF gt a as long as lt is a subset of gt.

#contract Source

contract :: forall lt gt f a. Alternative f => Contractable gt lt => VariantF gt a -> f (VariantF lt a)

A VariantF gt a can be cast to some VariantF lt a, where lt is is a subset of gt, as long as there is proof that the VariantF's runtime tag is within the subset of lt.

#VariantFShows Source

class VariantFShows (rl :: RowList) x  where

Members

Instances

Re-exports from Data.Symbol

#SProxy Source

data SProxy (sym :: Symbol)

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

Constructors

Re-exports from Data.Variant.Internal

#FProxy Source

data FProxy (a :: Type -> Type)

Proxy for a Functor.

Constructors

#Contractable Source

class Contractable gt lt 

Instances

#VariantFMatchCases Source

class VariantFMatchCases (rl :: RowList) (vo :: # Type) a b | rl -> vo a b

Instances