Test more GHC versions in travis

.travis.yml

@@ -1,5 +1,74 @@
+# Largely copied from https://github.com/ekmett/lens
+
 language: haskell
 
 branches:
   except:
     - gh-pages
+
+env:
+ - GHCVER=7.4.2
+ - GHCVER=7.6.3
+ - GHCVER=7.8.4
+ - GHCVER=7.10.1
+ - GHCVER=head
+
+matrix:
+  allow_failures:
+   - env: GHCVER=head
+
+before_install:
+  # If $GHCVER is the one travis has, don't bother reinstalling it.
+  # We can also have faster builds by installing some libraries with
+  # `apt`. If it isn't, install the GHC we want from hvr's PPA along
+  # with cabal-1.18.
+  - |
+    if [ $GHCVER = `ghc --numeric-version` ]; then
+      # Try installing some of the build-deps with apt-get for speed.
+      travis/cabal-apt-install --enable-tests $MODE
+      export CABAL=cabal
+    else
+      # Install the GHC we want from hvr's PPA
+      travis_retry sudo add-apt-repository -y ppa:hvr/ghc
+      travis_retry sudo apt-get update
+      travis_retry sudo apt-get install cabal-install-1.18 ghc-$GHCVER happy
+      export CABAL=cabal-1.18
+      export PATH=/opt/ghc/$GHCVER/bin:$PATH
+    fi
+  # Uncomment whenever hackage is down.
+  # - mkdir -p ~/.cabal && cp travis/config ~/.cabal/config && $CABAL update
+  - $CABAL update
+
+  # Update happy when building with GHC head
+  - |
+    if [ $GHCVER = "head" ] || [ $GHCVER = "7.8.3" ]; then
+      $CABAL install happy alex
+      export PATH=$HOME/.cabal/bin:$PATH
+    fi
+
+install:
+  - $CABAL install --dependencies-only --enable-tests
+  - $CABAL configure -flib-Werror --enable-tests $MODE
+
+script:
+ - $CABAL configure --enable-tests
+ - $CABAL build
+
+# Run tests
+ - $CABAL test
+
+# Check package for common errors
+# (enable after stable release)
+# - $CABAL check
+
+# Test that a source distribution can be built and installed
+# (enable after stable release)
+# - $CABAL sdist
+# - export SRC_TGZ=$($CABAL info . | awk '{print $2 ".tar.gz";exit}') ;
+#   cd dist/;
+#   if [ -f "$SRC_TGZ" ]; then
+#      $CABAL install --force-reinstalls "$SRC_TGZ";
+#   else
+#      echo "expected '$SRC_TGZ' not found";
+#      exit 1;
+#   fi