If you simply want color names to correspond to Ints, you can just define them at the top level:

red = 1 blue = 2 green = 3

What are you trying to gain here by having the color namespace? 2012/3/10 Ovidiu Deac :

Thanks for the answers. I guess my example with the colors was misleading. In that case it makes sense to use an abstract type.

In my case an abstract type is not ok. What I want is a set of int constants i.e. some names for some ints that I will use in my code, to avoid magic numbers in the code.

Of course I could define them like this: red = 1 blue = 2

...but that would pollute the namespace

Also I don't want to define them in a separate file. I would like to define them in the same file where I use them.

I already tried this approach:

module Main where

import ....

module Colors where   red = 1   blue = 2 .....

but the compiler complains at the line "module Colors where". It says: parse error on input `module'

...

In Haskell this would usually be an abstract type:

   data Color = Red | Blue | ...

You could then use functions to convert between integers and colors.

   fromColor :: Color -> Int    toColor   :: Int -> Maybe Color

You could also derive an Enum instance and get the conversion functions 'fromEnum' and 'toEnum' for free, although in that case the 'toEnum' function is less safe (no Maybe):

   data Color = Red | Blue | ...                 deriving Enum

   fromEnum :: Color -> Int    toEnum   :: Int -> Color

Greets, Ertugrul

-- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

A name space in Haskell is a module, and GHC only allows one module per file. So I would put these in a separate file, or do manual namespacing using prefixes, as in "colorRed". On Mar 10, 2012 11:14 AM, "Ovidiu Deac" wrote:

What are you trying to gain here by having the color namespace?

...

I want to avoid polluting the global namespace and to avoid name collisions.

As I said, the example with the colours wasn't probably a good one.

Let me change the question: How can I create a sub-namespace in the same file?

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

2012/3/10 Ovidiu Deac

I already tried this approach:

module Main where

import ....

module Colors where red = 1 blue = 2 .....

but the compiler complains at the line "module Colors where". It says: parse error on input `module'

Right, you can have only one module per file. You would define them in a separate file, possibly making use of qualified imports:

module Constants.AColors where red = 1 blue = 2

module Constants.BColors where yellow = 1 red = 2

module Main where import qualified Constants.AColors as AC import qualified Constants.BColors as BC ... -- code that uses AC.red and BC.red

This is not entirely ideal from the standpoint of using types to help manage your data, but without more details as to how you're using them, it's hard to present appropriate solutions. -- brandon s allbery allbery.b@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms