Re: [Haskell-cafe] Managing a sum type with a lot of constructors

My input I'm parsing into a data structure is URL query string like <key>=<value> and separated by a delimiter. Ultimately what I want back is of type `Data.Set.Set Text (v :: *)`. However I don't know how to represent that and don't want to build an HList like interface for it. On Wed, 23 Aug 2017 18:45:13 -0700 Michael Burge wrote:

If you have that many constructors, you probably aren't pattern-matching against the whole thing everywhere. So you could extract the few functions that use the entire type for case analysis into a typeclass, make each constructor its own type, and implement the typeclass:

Instead of:

something :: A -> IO () something A1 = putStrLn "hello" something (A2 _) = putStrLn "world"

Use:

data A1 data A2 = A2 Int

class RelatedConst a of something :: a -> IO ()

instance RelatedConst A1 where something _ = putStrLn "hello"

instance RelatedConst A2 where something _ = putStrLn "world"

Then, each declaration and instance could go in its own file.

If on the other hand, you are using lots of partial case matches everywhere, see if there are commonalities and extract a typeclass for each group

On Wed, Aug 23, 2017 at 6:29 PM, Adam Flott wrote:

...

I have a sum type with a lot of constructors and I'm not sure how to represent the type with maintainability in mind. For example,

data A = A1 | A2 Int | A3 Text Int32 Bool | ... | A100 Bool

Every inner type is concrete. There are 100+ constructors with no sign of ever getting reduced.

What technique would you recommend to keep the sum type approach but not having to define them all in one spot? I'm thinking 1 inner type + 1 function to construct per file (if that's possible). _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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