[Haskell-cafe] Manual type-checking in graphs: Avoidable?

[Tom Ellis]

On Fri, Feb 19, 2016 at 12:07:14PM +0100, Johannes Waldmann wrote:
> > .. a graph that described which people own which hamsters,
> 
> This is a bipartite graph, or, a relation. You want a type like
> 
> data Rel src tgt a =
>   Rel { fore :: ! ( M.Map src (M.Map tgt a) )
>       , back :: ! ( M.Map tgt (M.Map src a) )
>       }
> 
> where src = People, tgt = Hamster, and a = Bool.

I agree.  FGL seems inappropriate to model people owning hamsters because
you genuinely want to reflect the difference between people and hamsters by
having two different node types.