Hi, C:\Temp>yhc Main.hs -underscore Compiling Main ( Main.hs ) yhc: Prelude.head: empty list Answer: the -underscore flag enables this behaviour, the -underscore flag is broken, since its a real crash I can debug this pretty easy - i even have half an idea where its happening. Anyone want the -underscore flag to stick around, and not just be the default which can't be turned off? For that matter: Compliance Options: -underscore Enable H'98 underscore-is-lower-case (default=off) -puns Enable pre-98 named-field puns (default=on) -98 Haskell 98 compliance (default=off) Why is -98 off, why is -puns on (what are puns!!!) and lets kill this -underscore option. The n+k option died, others deserve to die too :) Thanks Neil