On Oct 8, 2009, at 11:43 , michael rice wrote:
This doesn't:
import System.Random
main = do
gen <- getStdGen
let (randNumber, newGen) = randomR (1,6) gen :: (Int, StdGen)
in putStrLn $ "Number is " ++ show randNumber
[michael@localhost ~]$ runhaskell zz.hs
zz.hs:4:2:
The last statement in a 'do' construct must be an expression
|
The problem here is that the "do" construct parses things a bit differently; if you're at the same indentation level, it inserts a (>>) on the assumption that the next line is an independent expression, so you need to indent the "in" a bit more to avoid it.
Note however that this usage is common enough that "do" provides a shorthand: you can simply omit the "in", and "let" will be parsed as if it were a statement:
> main = do
> gen <- getStdGen
> let (randNumber, newGen) = randomR (1,6) gen :: (Int,StdGen)
> putStrLn $ "Number is " ++ show randNumber
--
electrical and computer engineering, carnegie mellon university KF8NH