[Haskell-cafe] pythags

[Creighton Hogg]

On 2/12/07, phiroc at free.fr <phiroc at free.fr> wrote:
>
> 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


In the context of the tutorial, guard isn't defined until the next section:
additive monads.
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