Library Stdlib.extraction.ExtrHaskellNatInteger
Extraction of nat into Haskell's Integer
Disclaimer: trying to obtain efficient certified programs
by extracting nat into Integer isn't necessarily a good idea.
See comments in ExtrOcamlNatInt.v.
Extract Inductive nat => "Prelude.Integer" [ "0" "Prelude.succ" ]
"(\fO fS n -> if n Prelude.== 0 then fO () else fS (n Prelude.- 1))".