Choices, choices... Firstly, C uses an array not a list so you can too:

data Person = Person{ name :: UArray Int Char, age :: Int } deriving (Show)

Of course there is no bound on the type to be of length 10, the length would be bound at creation time:

stephen = Person { name = array (0,9) (zip [0..] "stephen") , age = 0 }

Quite horrible - but not significantly worse than C unless you believe the array size declator is defining the array type rather than just its storage size. Hmm. Sized types are a possibility but are quite advanced, certainly they give more 'static guarantees' than C provides (or just about anything else except dependent-types...). One example is here e.g: http://hackage.haskell.org/package/sized-types Tuples are another possibility but quite unwieldy: no special syntax, you would need to write conversion functions:

type Name = (Char,Char,Char,Char,Char,Char,Char,Char,Char,Char)

You could wrap a String inside a newtype and provide a special constructor, hiding the Name10 constructor via a module:

newtype Name10 = Name10 { getName10 :: String }

makeName10 :: String -> Name10 makeName10 s | length s > 10 = Name10 $ take 10 s | otherwise = Name10 s -- pad if you like here

Essentially it depends what you want to do with the sized string - generally you will loose string syntax[*] and all the list processing functions that work on strings as they are just lists of Char. This might not be a good balance for the safety you want. Best wishes Stephen [*] But you can overload string syntax for nefarious purposes (adding more complexity): http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extension... 2009/12/1 Srikanth K :

Hi,    I want to define a record say "Student".  The 'C' equvivalent for the same could be

struct Person {      char name[10]      int age }

The closest I can find for doing such a thing in haskell appears to be

data Person = Person{      name :: [char]      age :: Int }

I have not yet been able to find a suitable way to specify the constraint on the length of list(name in this case). So can someone let me know how we can impose this length constratint on the list  and derive a new type.

If standard haskell doesn't give this flexibility, are there any extensions in ghc to achieve the same. - Srikanth _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners