kure-2.14.0: Combinators for Strategic Programming

Portabilityghc
Stabilitybeta
MaintainerNeil Sculthorpe <neil@ittc.ku.edu>
Safe HaskellSafe-Inferred

Language.KURE.Lens

Contents

Description

This module defines the KURE Lens type, along with some useful operations.

Synopsis

Lenses

data Lens c m a b Source

A Lens is a way to focus on a sub-structure of type b from a structure of type a.

Instances

Monad m => Category (Lens c m) 

lens :: Translate c m a ((c, b), b -> m a) -> Lens c m a bSource

The primitive way of building a Lens. If the unfocussing function is applied to the value focussed on then it should succeed, and produce the same value as the original argument (of type a).

lensT :: Lens c m a b -> Translate c m a ((c, b), b -> m a)Source

Convert a Lens into a Translate that produces a sub-structure (and its context) and an unfocussing function.

focusR :: Monad m => Lens c m a b -> Rewrite c m b -> Rewrite c m aSource

Apply a Rewrite at a point specified by a Lens.

focusT :: Monad m => Lens c m a b -> Translate c m b d -> Translate c m a dSource

Apply a Translate at a point specified by a Lens.

pureL :: Monad m => (a -> b) -> (b -> a) -> Lens c m a bSource

Construct a Lens from two pure functions.

failL :: Monad m => String -> Lens c m a bSource

The failing Lens.

catchL :: MonadCatch m => Lens c m a b -> (String -> Lens c m a b) -> Lens c m a bSource

A Lens is deemed to have failed (and thus can be caught) if either it fails on the way down, or, crucially, if it would fail on the way up for an unmodified value. However, actual failure on the way up is not caught (as by then it is too late to use an alternative Lens). This means that, in theory, a use of catchL could cause a succeeding Lens application to fail. But provided lens is used correctly, this should never happen.

testLensT :: MonadCatch m => Lens c m a b -> Translate c m a BoolSource

Check if the focusing succeeds, and additionally whether unfocussing from an unchanged value would succeed.

bidirectionalL :: Monad m => BiTranslate c m a b -> Lens c m a bSource

Construct a Lens from a BiTranslate.

injectL :: (Monad m, Injection a g) => Lens c m a gSource

A Lens to the injection of a value.

projectL :: (Monad m, Injection a g) => Lens c m g aSource

A Lens to the projection of a value.