[Haskell-cafe] How is laziness defined?

[TJ]

I would think that with 100% laziness, nothing would happen until the
Haskell program needed to output data to, e.g. the console. Quite
obviously that's not it. So how is laziness defined in Haskell?

I remember vaguely someone saying that pattern matching on a value
forces it to be evaluated. Is that right? What else?

This is one of the things that just boggles my mind everytime I try to
wrap it around this thing called Haskell ;)

Cheers,

TJ