On Feb 12, 2007, at 11:02 AM, [EMAIL PROTECTED] 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
Add the line
import Control.Monad
to the beginning of your program. The 'guard' function is not
automatically in scope.
Rob Dockins
Speak softly and drive a Sherman tank.
Laugh hard; it's a long way to the bank.
-- TMBG
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