On Wed, Jul 11, 2007 at 12:57:53PM -0700, brad clawsie wrote:
> but i would like to be able to express some of these error cases in a
> more structured manner
okay, i'm going to answer my own question for the sake of documenting it
for others who might be interested. thanks to andrew and brandon for clues
module Main (main) where
data ErrorTestType = ErrorA | ErrorB Int | ErrorC String
instance Show ErrorTestType where
show ErrorA = "Error A"
show (ErrorB n) = "Error B:" ++ (show n)
show (ErrorC s) = "Error C:" ++ (show s)
type ErrorTestT = Either ErrorTestType
f :: IO (ErrorTestT String)
f = do
print "type something:"
s <- getLine
case length s of
1 -> return (Left ErrorA)
2 -> return (Left (ErrorB (length s)))
3 -> return (Left (ErrorC "error c"))
_ -> return (Right s)
main = do
r <- f
case r of
(Left e) -> print e
(Right a) -> print a
return ()
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