Use Haskell instead of bash in the installer

[jship]

PR for Haskell-ifying the installer.

[jship]

Having trouble with Travis where the vim plugin install is taking way too long: https://travis-ci.org/jship/haskell-vim-now/builds/243505406?utm_source=github_status&utm_medium=notification

This doesn't happen on my local Windows box. Shooting to reproduce this on my Mac tomorrow. Potentially a problem with Turtle.shell usage (https://github.com/begriffs/haskell-vim-now/pull/253/files#diff-29ed8a7e59b022f088bb09fc93c6df99R466) on Linux. On Windows, the nullShell helper is temporarily being used due to some weird behavior where the console write position is getting changed resulting in overwritten output.

[jship]

Looks like https://travis-ci.org/jship/haskell-vim-now/jobs/243507578 got passed the plugin install via use of nullShell and is now chugging along in the helper binary installs.

[jship]

Build 9 from my fork is green when helper binary install is skipped: https://travis-ci.org/jship/haskell-vim-now/builds/243786289?utm_source=github_status&utm_medium=notification

Build 8 timed out.

The CI build for this pull request (https://travis-ci.org/begriffs/haskell-vim-now/builds/243786312?utm_source=github_status&utm_medium=notification) failed because of the existing HVN install.

[begriffs]

I tried rebuilding on CI without cache, but the build still fails. I think the problem is this default repo path. It has already cloned the repo from my account, and then the new path conflicts:

The source repository path [https://github.com/jship/haskell-vim-now.git] does not match the
origin repository of the existing installation [https://github.com/begriffs/haskell-vim-now.git].
Please remove the existing installation [/home/travis/.config/haskell-vim-now] and try again.

[jship]

Thanks - updated it to the main repo.

[begriffs]

So I've been thinking about this PR. The changes are enormous (thanks for your hard work), is there a way to maybe start more gradually, like keep the bash scripting for the majority of the installer? We could delegate to a turtle Haskell script for one of the tasks you mentioned is tricky in bash.

A little time would verify that introducing the Haskell bit is stable for everybody. Then we could start increasing the amount of Haskell. I know it's nice to switch over entirely for Windows support, but I anticipate one big rewrite as introducing a lot of moving parts that could be difficult to debug.

[jship]

The gradual introduction sounds very reasonable to me. A couple good candidate areas:

1. neovim.sh
2. The setup_haskell portion of the installer.

neovim.sh is nice because it is completely standalone. I don't have that script's code implemented in this PR but can put together an equivalent Haskell script if we choose this as the intro Haskell portion.

The setup_haskell piece would be good to reduce the time taken when installing helper binaries. The Haskell version in this PR stack installs just the helper binary packages and nothing else. The bash version stack installs just about everything returned by the stack list-dependencies which is a big time-sink. The helper binaries are stored in a plain Haskell list and that list is fed as input to a mustache template to build the dependencies cabal file. This is a lot easier to work with/filter than doing the equivalent text munging in bash. The mustache template is embedded directly in the source so that makes for one less file in the repo too.

Let me know what you think. Should we close this PR? I can open a new one with just whatever we decide on.

[begriffs]

Let's try setup_haskell since it'll be sure to be hit whenever someone runs the installer and we'll get to work out any problems that way.

I'll close this PR and you can open another just for that part.