What steps will reproduce the problem? 1.cabal install --gobal xmonad-contrib

[ 10 of 226] Compiling XMonad.Layout.MultiToggle ( XMonad/Layout/MultiToggle.hs, dist/build/XMonad/Layout/MultiToggle.o )

XMonad/Layout/MultiToggle.hs:162:9: Could not deduce (HList b w0) arising from the ambiguity check for ‛??’ from the context (HList b w) bound by the type signature for (??) :: HList b w => a -> b -> HCons a b at XMonad/Layout/MultiToggle.hs:162:9-42 The type variable ‛w0’ is ambiguous In the ambiguity check for: forall a b w. HList b w => a -> b -> HCons a b To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the type signature for ‛??’: (??) :: HList b w => a -> b -> HCons a b Failed to install xmonad-contrib-0.11.2 cabal: Error: some packages failed to install: xmonad-contrib-0.11.2 failed during the building phase. The exception was: ExitFailure 1

What version of the product are you using? On what operating system? Ubuntu 13.10 ghc 7.7.20131127 xmonad-contrib-0.11.2

We don't really support GHC HEAD, as it changes too rapidly and may have bugs accidentally introduced. If you need to use HEAD, try it with the latest version instead of one from November.

A newer ghc HEAD isn't going to fix this (rejecting such "ambiguous types" is a feature not a bug). Instead build from darcs, which has a not-so-satisfactory fix, with a command like:

cabal install http://code.haskell.org/xmonad/xmonad.tar.gz http://code.haskell.org/XMonadContrib/xmc.tar.gz

I didn't want to commit to saying it was a HEAD bug, since I'm not keeping track and it did look like it was intended to be a feature; but such bugs have been known to creep in, and there's little point in pursuing further if it's not reproducible in the latest GHC.

Issue 565 has been merged into this issue.

This error still exists when building the current release version of xmonad/xmonad-contrib with GHC 7.8.2. Is there any chance that a fix for this issue could be made available on Hackage?

@ sim...@cryp.to. I originally filed the bug, and the suggested fix of compiling from darcs worked for me (it took a while to get around to it and I forgot to comment on the bug). Does it work for you?

Well, I can verify that adding the "ambiguous types" extension to the Cabal file remedies the issue.

I uploaded 0.11.3 which has the fix we put in darcs.