Copyright | (c) 2010-2011 Patrick Bahr |
---|---|

License | BSD3 |

Maintainer | Patrick Bahr <paba@diku.dk> |

Stability | experimental |

Portability | non-portable (GHC Extensions) |

Safe Haskell | None |

Language | Haskell98 |

This module defines some utility functions for deriving instances for functor based type classes.

- abstractNewtypeQ :: Q Info -> Q Info
- abstractNewtype :: Info -> Info
- normalCon :: Con -> (Name, [StrictType])
- normalCon' :: Con -> (Name, [Type])
- normalConExp :: Con -> Q (Name, [Type])
- normalConStrExp :: Con -> Q (Name, [StrictType])
- abstractConType :: Con -> (Name, Int)
- tyVarBndrName :: TyVarBndr -> Name
- containsType :: Type -> Type -> Bool
- containsType' :: Type -> Type -> [Int]
- newNames :: Int -> String -> Q [Name]
- tupleTypes :: Int -> Int -> [Name]
- derive :: [Name -> Q [Dec]] -> [Name] -> Q [Dec]
- liftSumGen :: Name -> Name -> Name -> Q [Dec]
- findSig :: [Name] -> [Dec] -> Q (Maybe ([Name], [Name]))

# Documentation

abstractNewtype :: Info -> Info Source

This function abstracts away `newtype`

declaration, it turns them into
`data`

declarations.

normalCon :: Con -> (Name, [StrictType]) Source

This function provides the name and the arity of the given data constructor.

normalCon' :: Con -> (Name, [Type]) Source

normalConStrExp :: Con -> Q (Name, [StrictType]) Source

Same as normalConExp' but retains strictness annotations.

abstractConType :: Con -> (Name, Int) Source

This function provides the name and the arity of the given data constructor.

tyVarBndrName :: TyVarBndr -> Name Source

This function returns the name of a bound type variable

containsType :: Type -> Type -> Bool Source

containsType' :: Type -> Type -> [Int] Source

newNames :: Int -> String -> Q [Name] Source

This function provides a list (of the given length) of new names based on the given string.

tupleTypes :: Int -> Int -> [Name] Source

derive :: [Name -> Q [Dec]] -> [Name] -> Q [Dec] Source

Helper function for generating a list of instances for a list of named
signatures. For example, in order to derive instances `Functor`

and
`ShowF`

for a signature `Exp`

, use derive as follows (requires Template
Haskell):

$(derive [makeFunctor, makeShowF] [''Exp])

liftSumGen :: Name -> Name -> Name -> Q [Dec] Source

This function lifts type class instances over sums
ofsignatures. To this end it assumes that it contains only methods
with types of the form `f t1 .. tn -> t`

where `f`

is the signature
that is used to construct sums. Since this function is generic it
assumes as its first argument the name of the function that is
used to lift methods over sums i.e. a function of type

(f t1 .. tn -> t) -> (g t1 .. tn -> t) -> ((f :+: g) t1 .. tn -> t)

where `:+:`

is the sum type constructor. The second argument to
this function is expected to be the name of that constructor. The
last argument is the name of the class whose instances should be
lifted over sums.