omit-generics aims to make deriving Eq and Ord instances
easier by giving the programmer control over what fields to ignore.
This is best explained by an example:
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE DerivingVia #-}
import GHC.Generics
import GHC.Generics.Omit
data Person = Person { name :: String, age :: Int, metadata :: [String] }
deriving stock Generic
deriving Eq via (Omit '["age", "metadata"] Person)Now, when we compare Person for equality, the age and metadata
fields are ignored!
Person "Steve" 43 ["loves cats"] == Person "Steve" 1 ["loves dogs", "is a baby"]
> True