Data.Function.Poly

Documentation

type family TypeListToArity xs r :: *

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 :: [*]

The inverse of TypeListToArity.

Equations

ArityToTypeList (x -> r) = x : ArityToTypeList r

ArityToTypeList r = `[]`

type family Result f :: *

Equations

Result (x -> r) = Result r

Result r = r

type family ArityMinusTypeList r xs :: *

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 ArityTypeListIso c l r = (ArityMinusTypeList c l ~ r, c ~ TypeListToArity l r)

type family InjectLast x f :: *

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 :: [*]

Equations

Append `[]` y = y : `[]`

Append (x : xs) y = x : Append xs y

type family ExpectArity xs f :: Constraint

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

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

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

Equations

Head (x : xs) = x

type family Tail xs :: [k]

Equations

Tail (x : xs) = xs

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

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

Methods

appN :: f -> HList xs -> result

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

Instances

ConsumeArity ([] *) r r

(ConsumeArity xs f r, ExpectArity ((:) * x xs) (x -> f)) => ConsumeArity ((:) * x xs) (x -> f) r

type family HasResult f r :: Constraint

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

Equations

HasResult r r = ()

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