This module defines the Accessor
type.
It should be imported with qualification.
- data T r a
- fromSetGet :: (a -> r -> r) -> (r -> a) -> T r a
- fromLens :: (r -> (a, a -> r)) -> T r a
- set :: T r a -> a -> r -> r
- (^=) :: T r a -> a -> r -> r
- compose :: [r -> r] -> r -> r
- get :: T r a -> r -> a
- (^.) :: r -> T r a -> a
- modify :: T r a -> (a -> a) -> r -> r
- (^:) :: T r a -> (a -> a) -> r -> r
- (.>) :: T a b -> T b c -> T a c
- (<.) :: T b c -> T a b -> T a c
- ($%) :: a -> (a -> b) -> b
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
(^=) :: 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
as infix operator.
This lets us write record^.field^.subfield
.
This imitates Modula II syntax.
(^:) :: 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)
.