Compile fail with GHC HEAD #41

snoyberg opened this Issue May 22, 2013 · 5 comments


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I get the following error message when using the newest GHC HEAD:

    Illegal instance declaration for ‛BufferType String’
      (All instance types must be of the form (T a1 ... an)
       where a1 ... an are *distinct type variables*,
       and each type variable appears at most once in the instance head.
       Use -XFlexibleInstances if you want to disable this.)
    In the instance declaration for ‛BufferType String’
Failed to install HTTP-4000.0.7

4000.2.8 compiles fine for me with GHC 7.7.20130720.

juhp commented Sep 7, 2013

base needs a version bump now as of 7.7.20130828

I opened a pull request for this in issue 46.


Same error with The Glorious Glasgow Haskell Compilation System, version 7.7.20130904 for 4000.2.8

schell commented Nov 7, 2013

I have the same issue, cabal versioning is forcing an attempt to compile 4000.0.7.

hsenag commented Mar 31, 2014

As far as I understand this is fixed or not reproducible in the latest version.

If there's a problem with cabal selecting an old version I'm not sure if there's anything much the HTTP package can do about it.

@hsenag hsenag closed this Mar 31, 2014
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