Do dependency analysis when kind-checking type declarations
This patch fixes Trac #4875. The main point is to do dependency analysis on type and class declarations, and kind-check them in dependency order, so as to improve error messages. This patch means that a few programs that would typecheck before won't typecheck any more; but before we were (naughtily) going beyond Haskell 98 without any language-extension flags, and Trac #4875 convinces me that doing so is a Bad Idea. Here's an example that won't typecheck any more data T a b = MkT (a b) type F k = T k Maybe If you look at T on its own you'd default 'a' to kind *->*; and then kind-checking would fail on F. But GHC currently accepts this program beause it looks at the *occurrences* of T.
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