Portability | TemplateHaskell |
---|---|
Stability | experimental |
Maintainer | Edward Kmett <ekmett@gmail.com> |
Safe Haskell | Trustworthy |
Control.Lens.TH
Description
- makeLenses :: Name -> Q [Dec]
- makeLensesFor :: [(String, String)] -> Name -> Q [Dec]
- makeClassy :: Name -> Q [Dec]
- makeClassyFor :: String -> String -> [(String, String)] -> Name -> Q [Dec]
- makeIso :: Name -> Q [Dec]
- makePrisms :: Name -> Q [Dec]
- makeLensesWith :: LensRules -> Name -> Q [Dec]
- defaultRules :: LensRules
- data LensRules = LensRules (String -> Maybe String) (String -> Maybe String) (String -> Maybe (String, String)) (Set LensFlag)
- lensRules :: LensRules
- classyRules :: LensRules
- isoRules :: LensRules
- lensIso :: Simple Lens LensRules (String -> Maybe String)
- lensField :: Simple Lens LensRules (String -> Maybe String)
- lensClass :: Simple Lens LensRules (String -> Maybe (String, String))
- lensFlags :: Simple Lens LensRules (Set LensFlag)
- data LensFlag
- simpleLenses :: Simple Lens LensRules Bool
- partialLenses :: Simple Lens LensRules Bool
- buildTraversals :: Simple Lens LensRules Bool
- handleSingletons :: Simple Lens LensRules Bool
- singletonIso :: Simple Lens LensRules Bool
- singletonRequired :: Simple Lens LensRules Bool
- createClass :: Simple Lens LensRules Bool
- createInstance :: Simple Lens LensRules Bool
- classRequired :: Simple Lens LensRules Bool
- singletonAndField :: Simple Lens LensRules Bool
- generateSignatures :: Simple Lens LensRules Bool
Constructing Lenses Automatically
makeLenses :: Name -> Q [Dec]
Build lenses (and traversals) with a sensible default configuration.
makeLenses = makeLensesWith lensRules
makeLensesFor :: [(String, String)] -> Name -> Q [Dec]
Derive lenses and traversals, specifying explicit pairings of (fieldName, lensName)
.
If you map multiple names to the same label, and it is present in the same constructor then this will generate a Traversal
.
e.g.
makeLensesFor [("_foo", "fooLens"), ("baz", "lbaz")] ''Foo makeLensesFor [("_barX", "bar"), ("_barY", "bar)] ''Bar
makeClassy :: Name -> Q [Dec]
Make lenses and traversals for a type, and create a class when the type has no arguments.
e.g.
data Foo = Foo { _fooX, _fooY ::Int
}makeClassy
''Foo
will create
class HasFoo t where foo ::Simple
Lens
t Foo instance HasFoo Foo where foo =id
fooX, fooY :: HasFoo t =>Simple
Lens
tInt
makeClassy = makeLensesWith classyRules
makeClassyFor :: String -> String -> [(String, String)] -> Name -> Q [Dec]
Derive lenses and traversals, using a named wrapper class, and specifying
explicit pairings of (fieldName, traversalName)
.
Example usage:
makeClassyFor "HasFoo" "foo" [("_foo", "fooLens"), ("bar", "lbar")] ''Foo
Make a top level isomorphism injecting into the type.
The supplied name is required to be for a type with a single constructor that has a single argument
e.g.
newtype List a = List [a] makeIso ''List
will create
list :: Iso [a] [b] (List
a) (List
b)
makeIso = makeLensesWith isoRules
makePrisms :: Name -> Q [Dec]
Configuring Lenses
makeLensesWith :: LensRules -> Name -> Q [Dec]
Build lenses with a custom configuration.
Default lens rules
data LensRules
This configuration describes the options we'll be using to make isomorphisms or lenses.
Rules for making fairly simple partial lenses, ignoring the special cases for isomorphisms and traversals, and not making any classes.
Rules for making lenses and traversals that precompose another lens.
lensIso :: Simple Lens LensRules (String -> Maybe String)
Lens to access the convention for naming top level isomorphisms in our lens rules.
Defaults to lowercasing the first letter of the constructor.
lensField :: Simple Lens LensRules (String -> Maybe String)
Lens to access the convention for naming fields in our lens rules.
Defaults to stripping the _ off of the field name, lowercasing the name, and rejecting the field if it doesn't start with an '_'.
lensClass :: Simple Lens LensRules (String -> Maybe (String, String))
Retrieve options such as the name of the class and method to put in it to build a class around monomorphic data types.
lensFlags :: Simple Lens LensRules (Set LensFlag)
Retrieve options such as the name of the class and method to put in it to build a class around monomorphic data types.
data LensFlag
Flags for lens construction
partialLenses :: Simple Lens LensRules Bool
Enables the generation of partial lenses, generating runtime errors for every constructor that does not have a valid definition for the lens. This occurs when the constructor lacks the field, or has multiple fields mapped to the same lens.
buildTraversals :: Simple Lens LensRules Bool
In the situations that a lens would be partial, when partialLenses
is
used, this flag instead causes traversals to be generated. Only one can be
used, and if neither are, then compile-time errors are generated.
handleSingletons :: Simple Lens LensRules Bool
Handle singleton constructors specially.
singletonRequired :: Simple Lens LensRules Bool
Expect a single constructor, single field newtype or data type.
createClass :: Simple Lens LensRules Bool
Create the class if the constructor is simple and the lensClass
rule matches.
createInstance :: Simple Lens LensRules Bool
Create the instance if the constructor is simple and the lensClass
rule matches.
generateSignatures :: Simple Lens LensRules Bool
Indicate whether or not to supply the signatures for the generated lenses.
Disabling this can be useful if you want to provide a more restricted type signature or if you want to supply hand-written haddocks.