12 Feb
2007
12 Feb
'07
11:14 a.m.
On Feb 12, 2007, at 11:02 AM, phiroc@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
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