Thanks all, So, in a do expression let x = 1 y = 2 etc. in z = 1 + 2 if <bool expr> then etc. else etc. Is this deviation documented somewhere? Michael --- On Thu, 10/8/09, Brandon S. Allbery KF8NH <allbery@ece.cmu.edu> wrote: From: Brandon S. Allbery KF8NH <allbery@ece.cmu.edu> Subject: Re: [Haskell-cafe] Let it be To: "michael rice" <nowgate@yahoo.com> Cc: "Brandon S. Allbery KF8NH" <allbery@ece.cmu.edu>, haskell-cafe@haskell.org Date: Thursday, October 8, 2009, 11:53 AM 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 -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.comsystem administrator [openafs,heimdal,too many hats] allbery@ece.cmu.eduelectrical and computer engineering, carnegie mellon university KF8NH