[Haskell-cafe] Over general types are too easy to make.
krismicinski at gmail.com
Sun Sep 2 21:10:20 CEST 2012
On Sun, Sep 2, 2012 at 12:06 PM, Alexander Solla <alex.solla at gmail.com> wrote:
> On Sun, Sep 2, 2012 at 9:40 AM, <timothyhobbs at seznam.cz> wrote:
>> The thing is, that one ALWAYS wants to create a union of types, and not
>> merely an ad-hock list of data declarations. So why does it take more code
>> to do "the right thing(tm)" than to do "the wrong thing(r)"?
> Because a union type is a complex union of parts, and the parts need to be
> deconstructed in order to be acted upon. There is not a unique way to do
> this -- different "unwrappings" have different properties and must match
> your use case.
> Perhaps you should read "Data types ala carte" (W. Swiestra) , which
> provides an approach to constructing "open" data types (i.e., sum types to
> which new summands can be added)
>  http://www.cs.ru.nl/~W.Swierstra/Publications/DataTypesALaCarte.pdf
If you're going to suggest that line of thinking you might also the
concept of rows in general.., though I'm not sure that's really quite
what he wants.
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