[Haskell-cafe] data types with overlapping component names (in one module)?

Sturdy, Ian sturdyi12 at mail.wlu.edu
Tue Apr 16 22:05:40 CEST 2013

I have seen some talk about fixing this, but none anywhere close to reality. As far as what you can use now, there are several libraries implementing alternatives to records; 'vinyl' uses type-level literal strings and is very slick (although all fields with the same name have the same type), while 'fields' uses template Haskell (and I think there are some others as well). I have used 'vinyl' a fair amount with great success; the others I cannot evaluate from experience.

From: haskell-cafe-bounces at haskell.org [haskell-cafe-bounces at haskell.org] on behalf of Johannes Waldmann [waldmann at imn.htwk-leipzig.de]
Sent: Tuesday, April 16, 2013 8:17 AM
To: haskell-cafe at haskell.org
Subject: [Haskell-cafe] data types with overlapping component names (in one     module)?

What is the current situation: can we have two types
with overlapping component names in one module?

module M where
data T1 = C1 { foo :: Int }
data T2 = C2 { foo :: String }

It seems not (ghc says: Multiple declarations of 'foo'). This comes close:
but still requires the definitions to reside in different modules?

This is a major pain (it forces me to spread the source over several files),
and also a show-stopper when selling Haskell to OO folks, who "naturally"
assume that a class also denotes a scope. (And that you could nest them.)

Are/were there plans/proposals to address this?

- J.W.

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