[Haskell-beginners] How to print the name of a variable

[Ozgur Akgun]

You're right, if you implement the type class independent of the value
you'll end up with associating names with types.

I use it as an interface to your method actually - sorry I didn't make it
clear enough.

So, something like this:

data NamedInt = NamedInt Int String

instance HasName NamedInt where
    name (NamedInt _ n) = n
    updateName n (NamedInt v _) = NamedInt v n

Now, if you want, you can have a Num instance for Named Int, redirect
everything to the inner-int, and here you go. You can use NamedInt as a Num
seamlessly.

Cheers,

On 20 March 2010 11:03, Stephen Tetley <stephen.tetley at gmail.com> wrote:

> Hi Ozgur
>
> Doesn't that associate names with types rather than names with values
> though:
>
> instance HasName Int where
>  name = "Int"
>
>
> > printWithName (1::Int)
> Int: 1
>
> > printWithName (70::Int)
> Int: 70
>
> I think the same is achievable with Data.Typeable / Data.Data although
> how to do it is somewhat buried...
>
> For associating names and values you'd still need to do it 'by hand'
> with something like
>
> data Named a = Named String a
>  deriving (Show)
>
> or
>
> type Named a = (String,a)
>
> Best wishes
>
> Stephen
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>



-- 
Ozgur Akgun
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