[Haskell-cafe] How to determine correct dependency versions for a library?

[eyal.lotem at gmail.com]

Especially in the case of base, not sure how upper bounds help at all:

If incompatible, you break with or without upper bounds. Actually getting errors related to Num instances is more informative IMO. 
If compatible, you just get false negatives and errors. 
In either case cabal can't install an older base to make the build work, so what do you gain?