Indeed, the question is not wherever it's a monad or not, just to what
extent is the monad useful.
Dne po 11. 7. 2016 22:08 uživatel Olaf Klinke
As someone else on this list whose name I don't recall put it, there is no choice on whether to make Stream a monad or not. It simply _is_ a monad. Anyone with some CS education hearing 'diagonal of inifinite list of infinite lists' should immediately think of Georg Cantor.
import Data.Stream import Data.Ratio
type Real = Stream Rational -- approximate a real number by an ascending stream -- of lower bounds.
supremum :: Stream Real -> Real supremum = join -- If a stream of reals is index-wise ascending, -- the monad instance for Stream computes its supremum. -- Use this e.g. to compute any mathematical quantity -- defined as a supremum.
-- Olaf