Given a sum type with an instance of Generic, This package lets you define producers for that sum type which the type checker expects to cover all of its constructors.
For example,
data T = First Int
| Second Bool
| Third String
deriving Generic
parseT :: Parser T
parseT
= getAlt
. total
. add First (Alt parseInt)
. add Second (Alt parseBool)
. add Third (Alt string)
$ end
If the parser were missing a branch for one of the constructors, you will get a type error. Unfortunately the type errors are usually not very helpful but may be improved in future versions.
The SumTotality module exports a simplified interface that expects all
constructors of the sum type to take a single argument. The
SumTotality.NArity module exports an interface that works with constructors
of any arity but has worse type errors.
Note that totality is only guaranteed if each constructor has different
arguments, otherwise you could potentially replace the constructor argument to
one of the adds with a different constructor of the same type.