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