On 17 February 2005 14:03, Ross Paterson wrote:

On Thu, Feb 17, 2005 at 01:40:31PM +0100, Mirko Rahn wrote:

...

The function Language.Haskell.Parser.parseModule behaves somehow strange and disagrees with ghc-6.* about the set of accepted inputs. An example:

-- file T1.hs: main = do args <- getArgs if null args then return [] else do ps <- mapM process args mapM print ps

The Report (section 9.3, especially notes 1 and 2) says "A nested context must be further indented than the enclosing context", so this is illegal. GHC and Hugs have innovated here, but only where the inner context is a do expression; they don't accept

f xs = case xs of y:ys -> case ys of z:zs -> zs

GHC also has a bug in this area which we discovered recently, and affects mixed layout/non-layout code. This is accepted, and it shouldn't be: f x = case x of False -> do { return x; } Cheers, Simon