Safe Haskell | None |
---|---|

Language | Haskell2010 |

- type family TypeListToArity xs r :: *
- type family ArityToTypeList r :: [*]
- type family Result f :: *
- type family ArityMinusTypeList r xs :: *
- type family InjectLast x f :: *
- type family Append xs x :: [*]
- type family ExpectArity xs f :: Constraint
- type family ExpectLast x f :: Constraint
- type family Head xs :: k
- type family Tail xs :: [k]
- class ExpectArity xs f => ConsumeArity xs f result | xs f -> result where
- appN :: f -> HList xs -> result

- type family HasResult f r :: Constraint

# Documentation

type family TypeListToArity xs r :: * 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`

.

TypeListToArity `[]` r = r | |

TypeListToArity (x : xs) r = x -> TypeListToArity xs r |

type family ArityToTypeList r :: [*] Source

The inverse of `TypeListToArity`

.

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

ArityToTypeList r = `[]` |

type family ArityMinusTypeList r xs :: * 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 `->`

.

ArityMinusTypeList r `[]` = r | |

ArityMinusTypeList (x -> r) (x : xs) = ArityMinusTypeList r xs |

type family InjectLast x f :: * Source

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

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

type family ExpectArity xs f :: Constraint Source

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

ExpectArity `[]` f = () | |

ExpectArity (x : xs) (x -> remainder) = ExpectArity xs remainder |

type family ExpectLast x f :: Constraint Source

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

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

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

type family Head xs :: k Source

Duplicate of singletons
`Head`

function for kind-polymorphic type-level lists.

Head (x : xs) = x |

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.

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.

ConsumeArity ([] *) r r Source | |

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