hugs bug?

[Johan Nordlander]

Philippe Faes wrote:
> 
> Hugs (version februari 2000) keeps reporting unexpected ';' or
> unexpected '}' in files that don't even contain those characters. I know
> very little about Haskell (I just started to try and study the language)
> so my haskell files will probably not be correct. Still with this kind
> of messages I have no clue of what to change in my programs. I don't
> know if this is a bug, or something I'm doing wrong.
> I'm using a Linux2.2 operating system on an i386 processor.
> 
> I attached a haskell source file (which is probably not even good
> haskell syntax), and the unexpected error message reported by hugs. The
> latter file was created typing:
> hugs tree.hs > hugserror.txt
> 
> Thank you,
> 
> Philippe Faes
> 
> mailto:Philippe.Faes@rug.ac.be
> 

Hi Philippe,

The ';' Hugs complains about is inserted automatically during lexical
analysis, as part of the layout handling process.  It marks the end of
one definition, and the beginning of another.  Often errors involving
these ghost ';'s indicate that the layout is wrong.

In your case, however, the source of the error is that you're using a
data declaration for defining a type synonym on line 16.  Since
[Lijstelem] is not a correct right-hand side for a data declaration, the
lexer assumes that the declaration of Lijst has ended and inserts a ';'.
 But since [Lijstelem] isn't a new declaration either, you get the error
you mentioned.  

Write

  type Lijst = [Lijstelem]

instead, and you'll be fine.

All the best,
Johan


>   ------------------------------------------------------------------------
> __   __ __  __  ____   ___      _________________________________________
> ||   || ||  || ||  || ||__      Hugs 98: Based on the Haskell 98 standard
> ||___|| ||__|| ||__||  __||     Copyright (c) 1994-1999
> ||---||         ___||           World Wide Web: http://haskell.org/hugs
> ||   ||                         Report bugs to: hugs-bugs@haskell.org
> ||   || Version: February 2000  _________________________________________
> 
> Haskell 98 mode: Restart with command line option -98 to enable extensions
> 
> Reading file "/usr/local/share/hugs/lib/Prelude.hs":
> Parsing       Dependency analysis                   Type checking             Compiling         Reading file "tree.hs":
> Parsing
> ERROR "tree.hs" (line 16): Syntax error in data type definition (unexpected `;', possibly due to bad layout)
> Prelude> [Leaving Hugs]
> 
>   ------------------------------------------------------------------------
> -- haskell
> -- poging tot implementeren van trees en optimal search tree
> -- *** tree.hs ***
> -- cf cursus G&S p430
> 
> -- nieuwe types
>   type Weight = Float
>   type Cost   = Float
>   type Failweight = Weight
>   type Token = Char
> 
> -- datastucturen
>   data Tree      = Failnode Weight | Branch Token Tree Tree
> 
>   data Lijst     = [Lijstelem]
>   data Lijstelem = Le Weight Failweight
> 
> -- functies
> q :: Int -> Lijst -> Weight
> q 0 (Lelm _ fw):ls = fw
> q i l:ls | i>0 = q i-1 ls
>          | i<0 = error "fout in q"
> 
> p :: Int -> Lijst -> Weight
> 
> c :: Int -> Int -> Lijst -> Weight
> c i i _ = 0
> c i j l = (w i j l) + zoekmin
> 
> w :: Int -> Int -> Lijst -> Weight
> w 0 0 []     = error "fout in lijstbewerking in tree.hs"
> w i i l = q i
> w i j l = (w i j-1 l) + (q j) +(p j)
> -- er wordt niet gecontroleerd of i>j; dat zou een fout moeten opleveren
> 
> zoekmin  :: Int -> Int -> Lijst -> Weight
> zoekmin i j l = (c i (zoekroot-1 l) l) + (c (zoekroot l) j l)
> 
> zookroot ::  Int -> Int -> Lijst -> Int
> --moet nog geimplementeerd worden
> 
> optboom :: Int -> Int -> Lijst -> Tree
> optboom i i l = Failnode (q i)
> optboom i j l = Branch (optboom i zoekroot) (zoekroot) (optboom (zoekroot+1) j)
>   -- deze syntax klopt niet