Re: type equality symbol

Lennart Augustsson wrote:

I agree. There are other ways that to solve the same problem as the case distinction does.

On Dec 7, 2007 12:45 PM, Johannes Waldmann mailto:waldmann@imn.htwk-leipzig.de> wrote:

On Fri, 7 Dec 2007, Manuel M T Chakravarty wrote:

> The problem is that Haskell 98 already messed that up. > If type functions are to use lower-case letters, [...]

Yes.

The broken thing is that the upper/lower case distinction has syntactic importance in the language definition at all.

I guess this was introduced to avoid writing out some declarations. This is a bad design goal, especially so for a declarative language.

I agree that it is problematic that type synonyms need to start with uppercase because this means that if you convert between multi-param type classes and associated types etc you need to change the case of the relevant type "variables" (ditto for parameterized modules vs translucent modules, both possible extensions). However in general I think having the case distinction is a good idea, since it provides these benefits: 1) Allows tyvars in types to be identified and implicitly quantified 2) Eliminates pattern matching errors caused by mis-spelling constructors (although Cayenne solves this by putting parentheses around constructors) 3) Avoids the chaos of individual programmers making up their own idiosyncratic conventions regarding where to use lowercase and where to use uppercase. Having the distinction built into the language therefore eliminates controversy ... ;-) There is nevertheless a tricky problem with 2 possible extensions: ML style translucent modules + typecase. typecase would need data types to be in uppercase since they are constructors of (*) whereas translucent modules would expect to be able to use a data type where the signature expected a type (which needs to be lowercase). Of course a solution could be: -- abstract/ translucent module acts as a signature module FOO where type t : * module Foo :> FOO where data T = ... type t = T but not module Foo :> FOO where data t = ... -- as in ML Regards, Brian.