Do not use Prelude; concoct our own Happy_Prelude alias (#325)

[sgraf812]

This is in order to undo a breaking change caused by users writing import Prelude hiding (null).

Fixes #325.

[sgraf812]

cabal.project to test the candidate:

packages:
  . 
  http://hackage.haskell.org/package/happy-lib-2.1.2/candidate/happy-lib-2.1.2.tar.gz
  http://hackage.haskell.org/package/happy-2.1.2/candidate/happy-2.1.2.tar.gz

[andreasabel]

Would HappyPrelude (CamlCase) be more in style of this codebase?

[andreasabel]

cabal.project to test the candidate:

packages:
  . 
  http://hackage.haskell.org/package/happy-lib-2.1.2/candidate/happy-lib-2.1.2.tar.gz
  http://hackage.haskell.org/package/happy-2.1.2/candidate/happy-2.1.2.tar.gz

I tested this with building Agda-2.6.4.3, and it worked fine!

[sgraf812]

Would HappyPrelude (CamlCase) be more in style of this codebase?

Perhaps, yes. On the other hand, all the other qualified imports are of the form Happy_Data_Array (for example). Furthermore, there is an alias type Happy_Int = Int#, so it's not like there is a fixed convention to follow.

I think I would prefer HappyPrelude, but if we switch to that case convention, we should do it consistently throughout the generated code. Not in this patch, though, and it is not an itch that I feel much of an urge to scratch.