Hello,
the "Advanced Monads" page in the Haskell Wikibook
(http://en.wikibooks.org/wiki/Haskell/Advanced_monads) contains the following
example of a List Monad
pythags = do
x <- [1..]
y <- [x..]
z <- [y..]
guard (x^2 + y^2 == z^2)
return (x, y, z)
However, whenever you load that function definition into Hugs or GHCi, you get a
message saying that "guard" is an undefined variable.
Does anyone know why?
Thanks.
phiroc
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