Quick reminder to Future Dave, as I’m going to assume he’ll keep making the same mistake Past and Present Daves make.
When switching between my editor and GHCi REPL to test stuff out I often forget to add a
deriving (Show, Eq) or similar line to my data types. This normally occurs after I’ve just set up a bit of test data in the REPL, so if I just fix the data declaration and
:reload GHCi then my setup will be lost. We can use the StandaloneDeriving GHC extension to help here.