Re: efficiency

By the way, I don't understand why Haskell98 provides both strictness flags and newtype declarations.... it seems to me that newtype M [a1 a2 ....] = MC (...) should be exactly the same as data N [b1 b2 ....] = NC !(...)

The Haskell report (in the "Datatype Renamings" section, 4.2.3, -- the one on newtype) explains the difference. Translating some of the examples there to your names, with

newtype M = M Int m (M i) = 42 data N = N !Int n (N i) = 42

we get Main> m undefined 42 but Main> n undefined *** Exception: Prelude.undefined mike