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Upgrading packages/Updating to GHC 7

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A list of common problems upgrading packages to GHC 7.

If you maintain packages, this is for you.

Contents

1 -XMonoLocalBinds

If you use -XGADTs or -XTypeFamilies you get -XMonoLocalBinds, which says that local let/where bindings are not auto-generalised. There's a blog post that explains the change, and what do to about it:

2 base 3 goes away

There is no base 3 now, after being deprecated for several years, so dependencies on base 3 won't compile with GHC 7.

3 -fglasgow-exts is deprecated

-fglasgow-exts is deprecated, and no longer enables GADTs or TypeFamilies. Use individual language flags (or better yet, pragmas) instead.

4 Quasiquotation data constructor modified

The QuasiQuoter constructor now takes four arguments instead of 2. (quoteType and quoteDec were added). One solution: use record syntax to set only the quoters you provide. This allows code to remain backwards compatible.

5 Quasiquotation: [$foo|...|] -> [foo|...|]

Quasiquoter invocation no longer requires a leading dollar sign. The leading dollar is now allowed, but deprecated.

6 Required library versions

A list of libraries and their earliest (known) GHC 7 ready version:

  • network >= 2.2.1.8
  • mtl >= 1.1.1.0
  • quickcheck >= 2.3.0.2
  • stringsearch >= 0.3.2