[Haskell-cafe] using Haskell more like scripting language

[Leandro Ostera]

Correct me if I’m wrong but isn’t this precisely where GADTs would excel?
On Sun, 29 Jul 2018 at 09:04, Dennis Raddle <dennis.raddle at gmail.com> wrote:

> Thanks Vanessa. The issue is that not everything will have a position or
> velocity. And some things will have more than those. There's a large
> overlapping set of possibilities that I can't quite predict until after
> I've finished several versions.
>
> However, I think I have a solution. This is actually in Purescript, which
> has has extensible record types. Each object will be represented by its own
> unique record, but there are mechanisms to write polymorphic code that
> operates on just portions of the records. I think that will get me through
> the first few versions of this program.
>
> Purescript also has dynamic types, but I suspect those will be hard to
> debug. When I'm developing code, I like to get helpful error messages.
> Please, no untraceable crashes from many levels deep in the stack. I don't
> know if that's what happens when a dynamic type fails to be the expected
> type, but I do know that these kinds of crashes are even harder to debug in
> Purescript than Haskell, as they happen in the compiled Javascript (which I
> don't understand much).
>
> D
>
> Mike
>
>
> On Sat, Jul 28, 2018 at 9:14 PM, Vanessa McHale <vanessa.mchale at iohk.io>
> wrote:
>
>> If everything you use will have a color, position, and velocity I'd just
>> use a product type, i.e.
>>
>> data itemState = ItemState Color Point Vector
>>
>> or even
>>
>> data ItemState = ItemState (Maybe Color) (Maybe Point) (Maybe Vector)
>>
>> Alternately, if you do want to go the dynamic route, `Data.Dynamic` in
>> `base` actually has some facilities for dynamic programming
>>
>> On 07/28/2018 05:04 PM, Dennis Raddle wrote:
>>
>> I'm actually working in Purescript, but the issue is pretty much the same
>> as one would encounter in Haskell.
>>
>> My application (animation of math-related ideas) is changing constantly.
>> It's research, and I don't know where I'll be with it next week, or even
>> tomorrow.
>>
>> For instance, the kinds of "objects" I'm animating (numbers, equations)
>> and the way they move and interact with each other is a research project,
>> and I'm constantly ripping out parts of my application and scavenging them
>> for variations on a theme.
>>
>> My objects need state. At this point I'm thinking of just putting the
>> state into a map with strings as keys and some kind of sum type to
>> represent each data item I might need.
>>
>> So if I want to represent that an object has a particular color and
>> position and velocity,
>>
>> itemState = M.fromList
>>   [("color"   , DataColor  blue       )
>>   ,("position", DataPoint  500.0 100.0)
>>   ,("velocity", DataVector 50.0 45.0  ) ]
>>
>> Which starts to look more like a dynamically-typed scripting language.
>> But it's not hard to work with. I can uses lenses/prisms to inspect and
>> update state, and it's okay if my program crashes on encountering malformed
>> state.
>>
>> What this lets me do is create new objects that mix and match parts of
>> old objects, and copy and paste a lot of the code.
>>
>> Is there a better way to do this? Is there a compromise I can make that
>> will allow the compiler to help me out more with finding errors at compile
>> time?
>>
>> D
>>
>>
>>
>>
>>
>>
>>
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