Data.Accessor.Basic

Description

This module defines the Accessor type. It should be imported with qualification.

Synopsis

Documentation

The access functions we propose, look very similar to those needed for List.mapAccumL (but parameter order is swapped) and State monad. They get the new value of the field and the record and return the old value of the field and the record with the updated field.

fromSetGet :: (a -> r -> r) -> (r -> a) -> T r aSource

fromLens :: (r -> (a, a -> r)) -> T r aSource

self :: T r rSource

Access the record itself

null :: T r ()Source

Access a (non-existing) element of type ()

set :: T r a -> a -> r -> rSource

Set the value of a field.

(^=) :: T r a -> a -> r -> rSource

set as infix operator. This lets us write first ^= 2+3 $ second ^= 5+7 $ record.

compose :: [r -> r] -> r -> rSource

This is a general function, but it is especially useful for setting many values of different type at once.

get :: T r a -> r -> aSource

Get the value of a field.

(^.) :: r -> T r a -> aSource

get as infix operator. This lets us write record^.field^.subfield. This imitates Modula II syntax.

modify :: T r a -> (a -> a) -> r -> rSource

Transform the value of a field by a function.

(^:) :: T r a -> (a -> a) -> r -> rSource

modify as infix operator. This lets us write field^:subfield^:(2*) $ record, record$%field^:subfield^:(2*) or record$%field^:subfield^:(const 1).

(.>) :: T a b -> T b c -> T a cSource

Accessor composition: Combine an accessor with an accessor to a sub-field. Speak "stack".

(<.) :: T b c -> T a b -> T a cSource

Accessor composition the other direction.

 (<.) = flip (.>)

($%) :: a -> (a -> b) -> bSource

Flipped version of '($)'.