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. (This was once up-to-date, but may have become in need of some attention. 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 SYB for generics. NFDataPDyn and GNFDataP modules will not be available.

A flag to assist debugging, affecting a few modules.