[Haskell] GADT: call for proper terminology

[Brian Hulley]

Doaitse Swierstra wrote:
> I would prefer notation like:
>
> data  Parser a      | Alt (Parser a) (Parser a)
>                     | Map ( b -> a)  (Parser b)
>                     | Succ a
>       Parser (a,b)  | Seq (Parser a) (Parser b)
>       Parser String | Lit (String -> Bool)
>       Parser [a]    | Many (Parser a)
>
> This takes away the noise in the heading of the current GHC notation
> (which is just plain confusing), and enables e.g. grouping of common
> alternatives,

The above is very similar to Bulat's proposal 
http://www.haskell.org/pipermail/haskell/2006-September/018466.html ie 
(adding the idea of using another layout block to group alternatives on the 
rhs):

    data
        Parser a  =
            Alt (Parser a) (Parser a)
            Map ( b -> a)  (Parser b)
            Succ a
       Parser (a,b) = Seq (Parser a) (Parser b)
       Parser String = Lit (String -> Bool)
       Parser [a] = Many (Parser a)

I don't think there's a good reason to use | to separate alternatives when 
we've already got {;} to form blocks of things, and to put things on the 
same line you'd just use:

    data {Hi Int = {One; Two; Three}; Hi a = Foo a}

This would also make it easier to replace the => syntax at some future point 
with the "guard-like" | syntax used in Clean (also suggested by Bulat in the 
above post).

Regards, Brian
-- 
Logic empowers us and Love gives us purpose.
Yet still phantoms restless for eras long past,
congealed in the present in unthought forms,
strive mightily unseen to destroy us.

http://www.metamilk.com