poly-arity-0.1.0: Tools for working with functions of undetermined arity

Data.Function.Poly

Synopsis

Documentation

type family TypeListToArity (xs :: [*]) (r :: *) :: * where ... Source #

Provide a type-level list of types xs, and a final result type r, construct a chain of arrows -> / n-ary function (which is right-associative) of each type in xs, ending in r.

Equations

 TypeListToArity '[] r = r TypeListToArity (x ': xs) r = x -> TypeListToArity xs r

type family ArityToTypeList (r :: *) :: [*] where ... Source #

The inverse of TypeListToArity.

Equations

 ArityToTypeList (x -> r) = x ': ArityToTypeList r ArityToTypeList r = '[]

type family Result (f :: *) :: * where ... Source #

Equations

 Result (x -> r) = Result r Result r = r

type family ArityMinusTypeList (r :: *) (xs :: [*]) :: * where ... Source #

Trim an n-ary function / chain of arrows -> with a type-level list of types xs, where each element of xs must unify with each element of the cons-list made with ->.

Equations

 ArityMinusTypeList r '[] = r ArityMinusTypeList (x -> r) (x ': xs) = ArityMinusTypeList r xs

type family InjectLast (x :: *) (f :: *) :: * where ... Source #

Injects a type to the base of the function arity chain.

Equations

 InjectLast x f = TypeListToArity (Append (ArityToTypeList f) x) (Result f)

type family Append (xs :: [*]) (x :: *) :: [*] where ... Source #

Equations

 Append '[] y = y ': '[] Append (x ': xs) y = x ': Append xs y

type family ExpectArity (xs :: [*]) (f :: *) :: Constraint where ... Source #

Inductively constrain a function's initial arity to match a type list; as a read-only style of static arity assurance.

Equations

 ExpectArity '[] f = () ExpectArity (x ': xs) (x -> remainder) = ExpectArity xs remainder

type family ExpectLast (x :: *) (f :: *) :: Constraint where ... Source #

Expect the last parameter in your stack of arity to have a type.

Equations

 ExpectLast x (x -> remainder) = () ExpectLast x (y -> remainder) = ExpectLast x remainder

type family Head (xs :: [k]) :: k where ... Source #

Duplicate of singletons Head function for kind-polymorphic type-level lists.

Equations

 Head (x ': xs) = x

type family Tail (xs :: [k]) :: [k] where ... Source #

Equations

 Tail (x ': xs) = xs

data HList xs where Source #

Constructors

 HNil :: HList '[] HCons :: (x :: *) -> HList xs -> HList (x ': xs)

class ExpectArity xs f => ConsumeArity xs f result | xs f -> result where Source #

Lift the HList's internal type-level list of types to a constraint context.

Minimal complete definition

appN

Methods

appN :: f -> HList xs -> result Source #

Use a heterogeneously-typed list of values as input to an n-ary function, where types must unify statically.

Instances

 ConsumeArity ([] *) r r Source # MethodsappN :: r -> HList [*] -> r Source # (ConsumeArity xs f r, ExpectArity ((:) * x xs) (x -> f)) => ConsumeArity ((:) * x xs) (x -> f) r Source # MethodsappN :: (x -> f) -> HList ((* ': x) xs) -> r Source #

type family HasResult (f :: *) (r :: *) :: Constraint where ... Source #

Shows that an n-ary function f precisely ends with r.

Equations

 HasResult r r = () HasResult (x -> r') r = HasResult r' r