Easy syntax question

Mike Gunter [email protected]
27 Aug 2001 12:44:45 -0700



Or, if you need several cases, you can use something like:


> funcGuard n | n `elem` [2,5,9]   = 5
>             | n `elem` [4,18]    = 1
>             | otherwise          = 7 
  
or, if you want an expression:

> caseGuard n     = case undefined of
>                    _ | n `elem` [2,5,9]   -> 5
>                      | n `elem` [4,18]    -> 1
>                      | otherwise          -> 7

        mike


Dean Herington <[email protected]> writes:

> Mark Carroll wrote:
> 
> > I can write a function x :: Integer -> Integer that returns 5 if I give it
> > 2, 5 or 9, or 7 otherwise. Say,
> >
> > x 2 = 5
> > x 5 = 5
> > x 9 = 5
> > x _ = 7
> >
> > Generally, this is a question about where multiple cases lead to the same
> > thing, maybe even in the middle of a function. (Like C's "case 1: case 2:
> > case 3: foo; break;".)
> >
> > Does it get any better than this, though? I can't convince 'case' to do
> > something like,
> >
> > case n of
> >   2,5,9 -> 5
> >   otherwise -> 7
> >
> > Am I missing some syntax somewhere? I'm lost in the grammar in the Haskell
> > report.
> >
> > -- Mark
> 
> I would write:
> 
> > if elem n [2,5,9] then 5 else 7
> 
> Dean