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: http://www.haskell.org/ghc/docs/7.6.2/html/users_guide/syntax-extns.html#dis... 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.
I'll just leave it here: http://hackage.haskell.org/trac/ghc/wiki/Records
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. -IRS ________________________________________ From: haskell-cafe-bounces@haskell.org [haskell-cafe-bounces@haskell.org] on behalf of Johannes Waldmann [waldmann@imn.htwk-leipzig.de] Sent: Tuesday, April 16, 2013 8:17 AM To: haskell-cafe@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: http://www.haskell.org/ghc/docs/7.6.2/html/users_guide/syntax-extns.html#dis... 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. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
On Tue, Apr 16, 2013 at 4:05 PM, Sturdy, Ian
'vinyl' uses type-level literal strings and is very slick (although all fields with the same name have the same type)
This is not entirely true, depending on what you mean by "name". The following is just fine. You only have naming issues if you want to give @Field::"baz":::Int@ a name, that name is, unsurprisingly, tied to the field type of Int. {-# LANGUAGE DataKinds, TypeOperators #-} import Data.Vinyl type Foo = '["baz" ::: Int] type Bar = '["baz" ::: String] x :: PlainRec Foo x = Field =: 2 y :: PlainRec Bar y = Field =: "Two" Anthony
-IRS ________________________________________ From: haskell-cafe-bounces@haskell.org [haskell-cafe-bounces@haskell.org] on behalf of Johannes Waldmann [waldmann@imn.htwk-leipzig.de] Sent: Tuesday, April 16, 2013 8:17 AM To: haskell-cafe@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: http://www.haskell.org/ghc/docs/7.6.2/html/users_guide/syntax-extns.html#dis... 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.
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
True, and thank you for clarifying that. I was thinking of the names of the field data, not the type-level name of the field:
name = Field :: "name" ::: String
-IRS
________________________________________
From: acowley@gmail.com [acowley@gmail.com] on behalf of Anthony Cowley [acowley@seas.upenn.edu]
Sent: Tuesday, April 16, 2013 6:13 PM
To: Sturdy, Ian
Cc: haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] data types with overlapping component names (in one module)?
On Tue, Apr 16, 2013 at 4:05 PM, Sturdy, Ian
'vinyl' uses type-level literal strings and is very slick (although all fields with the same name have the same type)
This is not entirely true, depending on what you mean by "name". The following is just fine. You only have naming issues if you want to give @Field::"baz":::Int@ a name, that name is, unsurprisingly, tied to the field type of Int. {-# LANGUAGE DataKinds, TypeOperators #-} import Data.Vinyl type Foo = '["baz" ::: Int] type Bar = '["baz" ::: String] x :: PlainRec Foo x = Field =: 2 y :: PlainRec Bar y = Field =: "Two" Anthony
-IRS ________________________________________ From: haskell-cafe-bounces@haskell.org [haskell-cafe-bounces@haskell.org] on behalf of Johannes Waldmann [waldmann@imn.htwk-leipzig.de] Sent: Tuesday, April 16, 2013 8:17 AM To: haskell-cafe@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: http://www.haskell.org/ghc/docs/7.6.2/html/users_guide/syntax-extns.html#dis... 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.
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
participants (4)
-
Anthony Cowley -
Artyom Kazak -
Johannes Waldmann -
Sturdy, Ian