Data.SOP.Dict

Explicit dictionaries.

When working with compound constraints such as constructed using All or All2, GHC cannot always prove automatically what one would expect to hold.

This module provides a way of explicitly proving conversions between such constraints to GHC. Such conversions still have to be manually applied.

This module remains somewhat experimental. It is therefore not exported via the main module and has to be imported explicitly.

Documentation

data Dict (c :: k -> Constraint) (a :: k) where

An explicit dictionary carrying evidence of a class constraint.

The constraint parameter is separated into a second argument so that Dict c is of the correct kind to be used directly as a parameter to e.g. NP.

Since: 0.2

Constructors

Dict :: c a => Dict c a

Instances

Show (Dict c a)

Defined in Data.SOP.Dict

Methods

showsPrec :: Int -> Dict c a -> ShowS

show :: Dict c a -> String

showList :: [Dict c a] -> ShowS

pureAll :: SListI xs => Dict (All Top) xs

A proof that the trivial constraint holds over all type-level lists.

Since: 0.2

pureAll2 :: All SListI xss => Dict (All2 Top) xss

A proof that the trivial constraint holds over all type-level lists of lists.

Since: 0.2

mapAll :: forall c d xs. (forall a. Dict c a -> Dict d a) -> Dict (All c) xs -> Dict (All d) xs

Lifts a dictionary conversion over a type-level list.

Since: 0.2

mapAll2 :: forall c d xss. (forall a. Dict c a -> Dict d a) -> Dict (All2 c) xss -> Dict (All2 d) xss

Lifts a dictionary conversion over a type-level list of lists.

Since: 0.2

zipAll :: Dict (All c) xs -> Dict (All d) xs -> Dict (All (c `And` d)) xs

If two constraints c and d hold over a type-level list xs, then the combination of both constraints holds over that list.

Since: 0.2

zipAll2 :: All SListI xss => Dict (All2 c) xss -> Dict (All2 d) xss -> Dict (All2 (c `And` d)) xss

If two constraints c and d hold over a type-level list of lists xss, then the combination of both constraints holds over that list of lists.

Since: 0.2

unAll_NP :: forall c xs. Dict (All c) xs -> NP (Dict c) xs

If we have a constraint c that holds over a type-level list xs, we can create a product containing proofs that each individual list element satisfies c.

Since: 0.2

unAll_POP :: forall c xss. Dict (All2 c) xss -> POP (Dict c) xss

If we have a constraint c that holds over a type-level list of lists xss, we can create a product of products containing proofs that all the inner elements satisfy c.

Since: 0.2

all_NP :: NP (Dict c) xs -> Dict (All c) xs

If we have a product containing proofs that each element of xs satisfies c, then All c holds for xs.

Since: 0.2

all_POP :: SListI xss => POP (Dict c) xss -> Dict (All2 c) xss

If we have a product of products containing proofs that each inner element of xss satisfies c, then All2 c holds for xss.

Since: 0.2

unAll2 :: Dict (All2 c) xss -> Dict (All (All c)) xss

Deprecated: 'All2 c' is now a synonym of 'All (All c)'

The constraint All2 c is convertible to All (All c).

Since: 0.2

all2 :: Dict (All (All c)) xss -> Dict (All2 c) xss

Deprecated: 'All2 c' is now a synonym of 'All (All c)'

The constraint All (All c) is convertible to All2 c.

Since: 0.2

withDict :: Dict c a -> (c a => r) -> r

If we have an explicit dictionary, we can unwrap it and pass a function that makes use of it.

Since: 0.2

hdicts :: forall h c xs. (AllN h c xs, HPure h) => h (Dict c) xs

A structure of dictionaries.

Since: 0.2.3.0