> you (and the compiler) will know and agree upon whether the same input will yield the same output What exactly does this mean? Haskell has plenty of non-dete

> you (and the compiler) will know and agree upon whether the same input will yield the same output What exactly does this mean? Haskell has plenty of non-deterministic functions — everything involving IO, for instance. I know that IO is non-deterministic, but how is that expressed within the language?