Re: [Haskell-cafe] Re: How does one get off haskell?

One way to avoid explicit, per-type unmarshalling is to use the existentialquantification extension to make a box type that you can store in a map, thus producing a heterogenous map of any types (with constraints). Cheers. ~Liam On 19 June 2010 04:08, aditya siram wrote:

I've written code with less bugs in Haskell than any other language I've used. And that's a credit to GHC and not because I'm a great programmer.

But I still don't know how to deal with the situation where you don't have a clear picture of your data  or heterogenous data that you are wrapping up in a type just to make the compiler happy?

Here's an example of the latter: I was writing some Haskell web app code where continuations are used to compose multi-step web transactions. The continuations were stored in a map keyed with a unique session id and invoked when the user POST'ed back that session id. The problem was that the map would only accept functions of one intermediate type and one result type. So I had to marshall/unmarshall all my functions to some common type (ContT () IO String  in my case) just so I could store it in the map - which felt kind of dirty.

While pointers on this particular problem would be appreciated, I think this is the kind of issue (needing to be flexible about data types) is a stumbling block for many beginning Haskell programmers.

-deech

On Fri, Jun 18, 2010 at 12:44 PM, Andy Stewart wrote:

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"Edward Z. Yang" writes:

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Excerpts from Bryan O'Sullivan's message of Fri Jun 18 13:16:58 -0400 2010:

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I'm inclined to disagree. It's precisely when the code is in a state of constant upheaval that I want the type system to be pointing out my dumb errors.

In my experience, the type system has forced me to care about thing that I don't want to care about (yet).  It's a different mindset: in the words of the prototyper: being first is valued over being correct.

This does mean that Haskell forces you to write long-term maintainable code from the get-go, yes. :-) Haha, that's true. :)

When i write Haskell code, it force me write *framework* code.

Sometimes, i wrote dirty code quickly, Haskell will told me :

  "Hey, bad code! Rewrite it! I don't accept dirty code ... bla bla ...".

Then i rewrite my code to make it flexible and maintainable.

Once you build beautiful framework code, you will find your life is so simple. :)

Cheers,

 -- Andy

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