data-accessor-template- Utilities for accessing and manipulating fields of records

Safe HaskellNone



This module provides an automatic Template Haskell routine to scour data type definitions and generate accessor objects for them automatically.



nameDeriveAccessors :: Name -> (String -> Maybe String) -> Q [Dec]Source

nameDeriveAccessors n f where n is the name of a data type declared with data and f is a function from names of fields in that data type to the name of the corresponding accessor. If f returns Nothing, then no accessor is generated for that field.

deriveAccessors :: Name -> Q [Dec]Source

deriveAccessors n where n is the name of a data type declared with data looks through all the declared fields of the data type, and for each field ending in an underscore generates an accessor of the same name without the underscore.

It is nameDeriveAccessors n f where f satisfies

 f (s ++ "_") = Just s
 f x = Nothing -- otherwise

For example, given the data type:

 data Score = Score { p1Score_ :: Int
 , p2Score_ :: Int
 , rounds :: Int

deriveAccessors will generate the following objects:

 p1Score :: Accessor Score Int
 p1Score = Accessor p1Score_ (\x s -> s { p1Score_ = x })
 p2Score :: Accessor Score Int
 p2Score = Accessor p2Score_ (\x s -> s { p2Score_ = x })

It is used with Template Haskell syntax like:

 $( deriveAccessors ''TypeName )

And will generate accessors when TypeName was declared using data or newtype.