[Haskell-cafe] Laziness question

From: http://en.wikibooks.org/wiki/Haskell/Laziness Given two functions of one parameter, f and g, we say f is stricter than g if f x evaluates x to a deeper level than g x Exercises    1. Which is the stricter function? f x = length [head x] g x = length (tail x) Prelude> let f x = length [head x] Prelude> let g x = length (tail x) Prelude> f undefined 1 Prelude> g undefined *** Exception: Prelude.undefined Prelude> So, g is stricter than f? Wouldn't both functions need to evaluate x to the same level, *thunk* : *thunk* to insure listhood? f x = length [head *thunk* : *thunk*] g x = length (tail *thunk* : *thunk*) Michael