wchogg at gmail.com
Mon Feb 12 11:12:25 EST 2007
On 2/12/07, phiroc at free.fr <phiroc at free.fr> wrote:
> the "Advanced Monads" page in the Haskell Wikibook
> (http://en.wikibooks.org/wiki/Haskell/Advanced_monads) contains the
> 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?
In the context of the tutorial, guard isn't defined until the next section:
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