[zmoazeni]

The post links to this page http://www.haskell.org/haskellwiki/Heterogenous_collections and one of other solutions is to use existential types to do it. But the author even said:

However, I don’t think this is a good use case. We can get around this problem in a cleaner and safer way by using the type system rather than subverting it.

[AnimalMuppet]

Right, I know he said that. But my point is, his solution doesn't scale well to a more complicated problem. (Unless I misunderstood either his solution or your point?)

[tel]

There are more real solutions which scale better, but in these toy problems it's hard to get to the meat of the problem. Sometimes the "existential antipattern" is a good choice (see Oleg's finally tagless encoding of, say, the linear lambda calculus). Sometimes creative use of static structure can scale much more neatly than lists of concrete objects.