Switch .travis.yml to hvr's mult-ghc-travis.

Author: mboes

.travis.yml

@@ -1,4 +1,26 @@
-language: haskell
+# Travis script based on https://github.com/hvr/multi-ghc-travis
 
-ghc:
- - '7.10'
+env:
+  - CABALVER=1.22 GHCVER=7.10.1
+
+before_install:
+  - travis_retry sudo add-apt-repository -y ppa:hvr/ghc
+  - travis_retry sudo apt-get update
+  - travis_retry sudo apt-get install cabal-install-$CABALVER ghc-$GHCVER
+  - export PATH=/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:$PATH
+
+install:
+  - cabal --version
+  - echo "$(ghc --version) [$(ghc --print-project-git-commit-id 2> /dev/null || echo '?')]"
+  - travis_retry cabal update
+  - cabal install --only-dependencies --enable-tests --enable-benchmarks
+
+script:
+  - cabal configure --enable-tests --enable-benchmarks -v2
+  - cabal build
+  - cabal test
+  - cabal check
+  - cabal sdist
+  # check that the generated source-distribution can be built & installed
+  - SRC_TGZ=$(cabal info . | awk '{print $2;exit}').tar.gz &&
+      (cd dist && cabal install --force-reinstalls "$SRC_TGZ")