Now I'm trying to use stack to install and run GCHJS. Can someone help me figure out this error? I first created project 'proj01' using the ghcjs template via stack new proj01 ghcjs Then I typed stack build It ran for a while, then gave an error messages that starts "While building custom Setup.hs for package semigroupoids-5.0.0.4 using .... <very long description>, Process exited with code ExitFailure 1" But it didn't halt. Instead it started compiling Main.hs, and ended up saying "at least the following dependencies are missing: tagged >= 0.8.5 && <1 && ==0.8.1" I tried adding "tagged" to the extra-deps in the stack.yaml, but it didn't help. While I'm posting, is there a resource that explains background to this? I don't know much about "packages," "snapshots," "dependencies", means of specifying versions, cabal, or YAML files. Everything I find online seems to assume some background knowledge of these things. For instance the stack documentation talks about snapshots, but I can't find an explanation that I understand for what a "snapshot" actually is. Ditto for all these many concepts that go into configuring and building. D