one-liner-instances

This package uses machinery from one-liner in order to provide default implementations for methods from Num, Fractional, Floating, Semigroup, and Monoid. These will work for any types (deriving Generic) that are made with one constructor, whose fields are all instances of that typeclass.

So, gPlus (generic addition) will work for:

data Tup1 a b = Tup1 a b            -- requires Num a, Num b
data Tup2 a   = Tup2 Int a          -- requires Num a, Num b
data Tup3     = Tup3 Int Double
data Tup4 a b = Tup4 Int Double     -- no constraint on a or b

But not on:

data Tup5 a   = Tup2 String a       -- String is not an instance of Num

These are implemented by applying the operation to every field.

Newtype wrappers

Similar to WrappedMonoid and WarppedMonad from base, some convenient newtype wrappers are provided that will give free instances of Num, etc. for appropriate types:

If a is a data type (deriving Generic) with a single constructor whose fields all have instances of Num, then GNum a has a Num instance (and same for Fractional, Floating, etc.).

If a is a data type (deriving Generic) with a single constructor whose fields all have instances of Semigroup, then GMonoid a has a Semigroup instance (and same for Monoid).