Sacrifice generic deriving, the NFDataPDyn module, and a couple functions from the PatAlg module, in exchange for true Haskell98 conformance (portability). You need to set PARALLELISM_EXPERIMENT, USE_WW_DEEPSEQ, USE_SOP, and NFDATA_INSTANCE_PATTERN to False if you set HASKELL98_FRAGMENT to True. (One thing it insists on is -XPatternGuards, although this could be relieved in the obvious way...)

We can selectively use par instead of seq, which is interesting.

The SOP generic function is probably more performant, anyway! (This will be forced False if HASKELL98_FRAGMENT is True.)

Depend on deepseq and deepseq-generics, to provide conditional deep forcing. This is optional.

For NFDataP, if a pattern match fails a warning is output to stderr.

Use the generics-sop package instead of GHC.Generics (in GNFDataN) and instead of SYB (in NFDataPDyn). If USE_SOP is False, and NFDataPDyn, GNFDataP, and GSeqable modules will not be available. Also, if USE_SOP is False, then JUST_ALIAS_GSEQABLE must be False (this is not done for you; the language of Cabal flags makes it hard to write such logic, probably by design!...).

A flag to assist debugging, affecting a few modules.