Data.Record.Field.Indexable

Composition operators for collection fields.

Documentation

class Indexable a i where

Class of collection types that can be indexed into.

TODO: This should probably be a single-parameter type class with two associated types instead.

Associated Types

type Element a :: *

Methods

indexGet :: i -> a -> Maybe (Element a)

indexSet :: i -> Maybe (Element a) -> a -> a

unsafeIndexGet :: i -> a -> Element a

Instances

Indexable IntSet Int

Integral i => Indexable [a] i

Indexable (IntMap a) Int

(a1 ~ a2, Ord a1) => Indexable (Set a1) a2

(i1 ~ i2, IArray a e, Ix i1) => Indexable (a i1 e) i2

(k1 ~ k2, Ord k1) => Indexable (Map k1 a) k2

(#!) :: (Field a, Indexable (Dst a) i) => a -> i -> Src a :-> Maybe (Element (Dst a))

Compose a field with an Indexable collection safely.

 r .# coll #! idx

returns Nothing if idx was not found from the collection, and Just v if v was found.

 r .# coll #! idx =: Just v

sets the value at idx in the collection to be v. If the value wasn't in the collection, it's inserted. The exact semantics of insertion depend on the actual collection in question.

 r .# coll #! idx =: Nothing

removes the value at idx from the collection, if possible.

(#!!) :: (Field a, Indexable (Dst a) i) => a -> i -> Src a :-> Element (Dst a)

As (#!), but reading a nonexistent value will likely result in a bottom value being returned. Also, the resulting field cannot be used to remove values.