Stefan O'Rear
Indeed, you've caught on an important technical distinction.
Lazy: Always evaluating left-outermost-first.
I think most people would rather use the term "normal order¨ for that; lazy means evaluating in normal order /and/ not evaluating the same expression twice. normal order: (\a -> a + a) (2+2) => (2+2) + (2+2) => 4 + (2+2) => 4 + 4 => 8 lazy: (\a -> a + a) (2+2) => (2+2) + (2+2) -- but we still know that both these (2+2)s are the same => 4 + 4 => 8 That might be slightly confusing because I've used (+), which is strict. It might have been better to use Ss and Ks, but less succinct...
Non-strict: Behaving as if it were lazy.
non-strict: giving the same answers as if it were normal order. A haskell implementation could, in principle, conform to the non-strict requirement without doing any of the update in place that makes laziness.
Haskell's semantics are non-strict in nature, but there is no requirement for laziness. All optimizing haskell compilers are non-lazy.
???? -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk