Haskell — any easy way to put Data.Dynamic's in a Map?

Question

I want to map Data.Dynamics to other Data.Dynamics. But, I can't write

Map Dynamic Dynamic

because there's no Ord Dynamic. Is there any solution (like a version of Dynamic whose toDyn function only accepts Ord things, and reifies the typeclass upon boxing?)

The motivation for this is to have a map from Variables --> Values inside an EDSL compiler. (Clearly the variables can have different types). edit: Sorry, it's not necessary for this problem, I can/should just store the variable name as the key. But, I'm still interested in the question.

Thanks in advance!!

Answer 1

I hacked a solution if anyone is interested; it's a little tricky / fun :)

Code here: http://pastebin.com/KiJqqmpj .

(I also wrote one for higher-order types, which saves you the need of writing a Typeable1, if you always have the same higher-order type function: http://pastebin.com/aqjwFv9p . In some cases, writing Typeable1 instances can be hard.)

Some values:

float1 = mk_ord_dyn (1 :: Float)
float2 = mk_ord_dyn (2 :: Float)
int1 = mk_ord_dyn (1 :: Int)
int2 = mk_ord_dyn (2 :: Int)

A little test,

*OrdDynamic> int1 == int1
True
*OrdDynamic> int2 == int2
True
*OrdDynamic> int1 < int2
True
*OrdDynamic> int2 < float1
False
*OrdDynamic> float1 < int2
True
*OrdDynamic> int1 == float1
False

Answer 2

No, there is no way. By the types involved in the creating Dynamic there cannot be. If you want to be impure you can use StablePtr, but that's the best I can think of.

But by changing the type of toDyn to include Ord it can be done.