details here - https://github.com/JPMoresmau/scion-class-browser/issues/4
This is probably due to lose conduit dependency. Meanwhile, I will try to compile scion-browser with different versions of conduit and see what happens.
Ok, I just tried compiling it with different conduit library version (originally I have used latest conduit-0.5.5):
cabal install -with-compiler="/home/evgenij/programming/haskell/compilers/ghc-7.4.2/bin/ghc" scion-browser-0.2.12 -constraint=conduit==0.4.0
On GHC-7.6.1 it did not compile at all, because some dependencies needed to be rebuild to older versions and they can't be rebuilded with new compiler.
On GHC-7.4.2 it also needed to rebuild some dependencies, but it did compile without errors.
It seems only the latest version of conduit (0.5.5) does not let scion-browser-0.2.12 compile. The previous version - 0.5.4.2 - compiles on both compilers.
Yep, Michael Snoyman has confirmed that a change in conduit has broken that code, and provided me with the solution, will upload the fixed code to github today.