On 2004-07-26 at 18:10BST =?iso-8859-1?q?Stu=20White?= wrote:

Hi

I'm not especially experienced in using haskell, and I could use some help.

As part of a project, I'm trying to construct a data type that can represent three values as a 'triple' (as opposed to a 'tuple'),

you could just use triples: (a,b,c)

and then make a function so that I can sort these values into ascending order.

I'm having a few problems with the code that I have at the minute (I suspect its riddled with errors!)

type Triple = Triple {

"type" is essentially for renaming types, you want "data" here.

entry 1 :: a;

You can't have spaces in field names. Make those changes and see what hugs or ghci says to it.

<DIV>Hi</DIV>

(and more html snipped) Please don't send html messages to the list! Jón -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk

Stu White writes:

type Triple = Triple {

data Triple = Triple { -- 'type' is for synonyms, 'data' for user-defined

entry 1 :: a; entry 2 :: a; entry 3 :: a;

entry_1 :: a; -- field names must be a single identifier entry_2 :: a; entry_3 :: a;

sortTriple :: Triple a -> Triple a;

sortTriple :: (Ord a) => Triple a -> Triple a -- an ordering constraint on the 'a' is implied

} deriving (Show, Eq) where

-- You can't have a 'where' clause on a datatype definition. Presumably you -- are trying to express that the 'sortTriple' component is invariant. If -- so, then remove it from the datatype and write it at the toplevel. If -- you rather mean that it has a default definition that can be overridden, -- then you can keep it in the datatype, but you will need to add the default -- functional value to each new Triple you create, perhaps with a 'smart' -- constructor: -- mkTriple x y z = Triple x y z sortTriple

sortTriple t@(Triple x y z) | (y

sortTriple t@(Triple x y z s) -- you omitted the fourth component of the Triple | (y