Data.Accessor
Description
This module provides a simple abstract data type for a piece of a data stucture that can be read from and written to. In contrast to Data.Accessor.Basic it is intended for unqualified import.
- type Accessor r a = T r a
- accessor :: (r -> a) -> (a -> r -> r) -> Accessor r a
- setVal :: Accessor r a -> a -> r -> r
- (^=) :: T r a -> a -> r -> r
- getVal :: Accessor r a -> r -> a
- (^.) :: r -> T r a -> a
- (^:) :: T r a -> (a -> a) -> r -> r
- getA :: Monad m => Accessor r a -> StateT r m a
- putA :: Monad m => Accessor r a -> a -> StateT r m ()
- (=:) :: Monad m => Accessor r a -> a -> StateT r m ()
- (%=) :: Monad m => T r a -> a -> StateT r m ()
- modA :: Monad m => Accessor r a -> (a -> a) -> StateT r m ()
- (%:) :: Monad m => T r a -> (a -> a) -> StateT r m ()
- (.>) :: Accessor a b -> Accessor b c -> Accessor a c
- (<.) :: Accessor b c -> Accessor a b -> Accessor a c
Documentation
type Accessor r a = T r aSource
An Accessor r a is an object that encodes how to
get and put a subject of type a out of/into an object
of type s.
In order for an instance of this data structure a to be
an Accessor, it must obey the following laws:
getVal a (setVal a x r) = x setVal a (getVal a r) r = r
Arguments
| :: (r -> a) | get method |
| -> (a -> r -> r) | set method |
| -> Accessor r a |
Construct an Accessor from a get and a set method.
Arguments
| :: Accessor r a | record field |
| -> a | value |
| -> r | original record |
| -> r | new record with field |
Set a value of a record field that is specified by an Accessor
(^=) :: T r a -> a -> r -> rSource
set as infix operator.
This lets us write first ^= 2+3 $ second ^= 5+7 $ record.
Arguments
| :: Accessor r a | record field |
| -> r | record |
| -> a | value of the field in the record |
Get a value from a record field that is specified by an Accessor
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).
getA :: Monad m => Accessor r a -> StateT r m aSource
A structural dereference function for state monads.
putA :: Monad m => Accessor r a -> a -> StateT r m ()Source
A structural assignment function for state monads.
(=:) :: Monad m => Accessor r a -> a -> StateT r m ()Source
An "assignment operator" for state monads.
(=:) = putA
modA :: Monad m => Accessor r a -> (a -> a) -> StateT r m ()Source
A structural modification function for state monads.