This module contains Template Haskell code that can be used to automatically generate the boilerplate code for the generic deriving library.

To use these functions, pass the name of a data type as an argument:

{-# LANGUAGE TemplateHaskell #-} data Example a = Example Int Char a $(deriveGeneric ''Example) -- Derives Generic instance $(deriveGeneric1 ''Example) -- Derives Generic1 instance $(deriveGenericAnd1 ''Example) -- Derives Generic and Generic1 instances 

This code can also be used with data families. To derive for a data family instance, pass the name of one of the instance's constructors:

{-# LANGUAGE FlexibleInstances, TemplateHaskell, TypeFamilies #-} data family Family a b newtype instance Family Char x = FamilyChar Char data instance Family Bool x = FamilyTrue | FamilyFalse $(deriveGeneric 'FamilyChar) -- instance Generic (Family Char b) where ... $(deriveGeneric1 'FamilyTrue) -- instance Generic1 (Family Bool) where ... -- Alternatively, one could type $(deriveGeneric1 'FamilyFalse) 

General usage notes

Template Haskell imposes some fairly harsh limitations on ordering and visibility within a module. In most cases, classes derived generically will need to be derived using StandaloneDeriving after the deriveGeneric* invocation. For example, if Generically is a class that uses a Generic constraint for its instances, then you cannot write

data Fish = Fish deriving Show via (Generically Fish) $(deriveGeneric 'Fish) 

You must instead write

data Fish = Fish $(deriveGeneric 'Fish) deriving via Generically Fish instance Show Fish 

Furthermore, types defined after a deriveGeneric* invocation are not visible before that invocation. This may require some careful ordering, especially in the case of mutually recursive types. For example, the following will not compile:

data Foo = Foo | Bar Baz $(deriveGeneric 'Foo) data Baz = Baz Int Foo $(deriveGeneric 'Baz) 

Instead, you must write

data Foo = Foo | Bar Baz data Baz = Baz Int Foo $(deriveGeneric 'Foo) $(deriveGeneric 'Baz)