Resolving dependencies... cabal: Could not resolve dependencies: next goal: happstack-clientsession (user goal) rejecting: happstack-clientsession-7.3.0, 7.2.7, 7.2.6, 7.2.5, 7.2.4, 7.2.3, 7.2.2 (global constraint requires ==7.2.1) trying: happstack-clientsession-7.2.1 trying: base-4.8.1.0/installed-4f7... (dependency of happstack-clientsession-7.2.1) trying: transformers-base-0.4.4 (dependency of happstack-clientsession-7.2.1) trying: transformers-0.4.2.0/installed-21d... (dependency of transformers-base-0.4.4) next goal: mtl (dependency of happstack-clientsession-7.2.1) rejecting: mtl-2.2.1, 2.2.0.1, 2.2 (conflict: happstack-clientsession => mtl>=2.0 && <2.2) rejecting: mtl-2.1.3.1, 2.1.2 (conflict: transformers==0.4.2.0/installed-21d..., mtl => transformers==0.3.*) rejecting: mtl-2.1.1, 2.1 (conflict: base==4.8.1.0/installed-4f7..., mtl => base<4.6) rejecting: mtl-2.0.1.1 (conflict: transformers==0.4.2.0/installed-21d..., mtl => transformers==0.2.*) rejecting: mtl-2.0.1.0, 2.0.0.0 (conflict: base==4.8.1.0/installed-4f7..., mtl => base<4.6) rejecting: mtl-1.1.1.1, 1.1.1.0, 1.1.0.2, 1.1.0.1, 1.1.0.0, 1.0 (conflict: happstack-clientsession => mtl>=2.0 && <2.2) Backjump limit reached (change with --max-backjumps).