Data.Accessor.Template

data-accessor-template-0.2.1.12: Utilities for accessing and manipulating fields of records

Safe Haskell | None
Language | Haskell98

Data.Accessor.Template

Description

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

Synopsis

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

# Documentation

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

`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]

`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`.