Safe Haskell	Safe
Language	Haskell98

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.

Synopsis

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 a Source #

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

accessor Source #

Arguments

:: (r -> a)	get method
-> (a -> r -> r)	set method
-> Accessor r a

Construct an Accessor from a get and a set method.

setVal Source #

Arguments

:: Accessor r a	record field `f`
-> a	value `x` to be set
-> r	original record
-> r	new record with field `f` changed to `x`

Set a value of a record field that is specified by an Accessor

(^=) :: T r a -> a -> r -> r infixr 5 Source #

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

getVal Source #

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

(^.) :: r -> T r a -> a infixl 8 Source #

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

(^:) :: T r a -> (a -> a) -> r -> r infixr 5 Source #

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 a Source #

Deprecated: Data.Accessor.Monad.Trans.State.get from data-accessor-transformers package

A structural dereference function for state monads.

putA :: Monad m => Accessor r a -> a -> StateT r m () Source #

Deprecated: Data.Accessor.Monad.Trans.State.set from data-accessor-transformers package

A structural assignment function for state monads.

(=:) :: Monad m => Accessor r a -> a -> StateT r m () infix 1 Source #

Deprecated: use (Data.Accessor.Monad.Trans.State.%=) from data-accessor-transformers package

An "assignment operator" for state monads.

(=:) = putA

(%=) :: Monad m => T r a -> a -> StateT r m () infix 1 Source #

Infix variant of set.

modA :: Monad m => Accessor r a -> (a -> a) -> StateT r m () Source #

Deprecated: Data.Accessor.Monad.Trans.State.modify from data-accessor-transformers package

A structural modification function for state monads.

(%:) :: Monad m => T r a -> (a -> a) -> StateT r m () infix 1 Source #

Infix variant of modify.

(.>) :: Accessor a b -> Accessor b c -> Accessor a c infixl 9 Source #

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

(<.) :: Accessor b c -> Accessor a b -> Accessor a c infixr 9 Source #

Accessor composition the other direction.

(<.) = flip (.>)

You may also use the (.) operator from Category class.