Data.Dependent.Map examples

Question

Are there any examples anywhere of how to use the DMap type? The package documentation is very learned, and I know it if for reference only, but it is singularly unhelpful for one getting started. Google reveals nothing that I can see.

Hardfavored

What problem are you trying to solve that you think DMap will help you with? – Underestimate

I was thinking maybe it could be used to make a map where the values may have any different type depending on the type of key. – Hardfavored

Well, there is one in the README – Denizen

DMap is used very heavily in reflex, so you can take a look at that package. – Clem

Answer 1

From the Updated README.md example pull request. One need to implement GEq and GCompare instances for a GADT:

data Foo a where
  AnInt   :: Foo Int
  AString :: Foo String

deriveGEq      ''Foo
deriveGCompare ''Foo

dmap1 :: DMap Foo Identity
dmap1 = fromList [AnInt ==> 1, AString ==> "bar"]

main = do
  print $ dmap1 ! AnInt
  print $ dmap1 ! AString

Pecos