Control.Reference.TH.Generate

This module can be used to generate references for record fields. If the field surely exists, a Lens will be generated. If the field may not exist, it will be a Partial lens.

It will have the maximum amount of polymorphism it can create.

If the name of the field starts with "_", the name of the field will be the same with "_" removed. If not, the reference name will be the field name with "_" added te the start.

The following code sample:

data Maybe' a = Just' { _fromJust' :: a }

              | Nothing'

$(makeReferences ''Maybe)



data Tuple a b = Tuple { _fst' :: a, _snd' :: b }

$(makeReferences ''Tuple)

Is equivalent to:

data Maybe' a = Just' { _fromJust' :: a }

              | Nothing'

              

fromJust' :: Partial (Maybe' a) (Maybe' b) a b

fromJust' = partial (case Just' x -> Right (x, y -> return (Just' y))

                           Nothing' -> Left (return Nothing'))



data Tuple a b = Tuple { _fst' :: a, _snd' :: b }

fst' :: Lens (Tuple a c) (Tuple b c) a b

fst' = lens _fst' (b tup -> tup { _fst' = b })

snd' :: Lens (Tuple a c) (Tuple a d) c d

snd' = lens _snd' (b tup -> tup { _snd' = b })

Documentation

makeReferences :: Name -> Q [Dec]

Creates references for fields of a data structure.

debugTH :: Q [Dec] -> Q [Dec]

Shows the generated declarations instead of using them.