Feature request: spago script

[Unisay]

I'd ❤️ to have an analog of stack's script feature:
https://docs.haskellstack.org/en/stable/GUIDE/#script-interpreter
https://www.fpcomplete.com/haskell/tutorial/stack-script/#running-a-script

Example:

$ head myscript.ps

outputs:

#!/usr/bin/env spago
-- spago script
import Prelude
...

then

$ chmod u+x myscript.ps
$ ./myscript.ps

[klntsky]

The obvious problem are node.js dependencies (spago does not manage them).

I guess it's possible to write a tiny wrapper over npm (built-in into spago) that would handle them. Would be cool!

[f-f]

@klntsky we'll start dealing with "install NPM dependencies" once we switch to the new registry (which keeps track of these), so I'd say it's fine to add them here.

We already have the flag --dependency in spago repl which we could reuse here, and we could just introduce a --npm-dependency flag here to deal with NPM stuff.

However, a first implementation of this feature should not care about NPM stuff at all and just do the PureScript side of things - which I suspect it would solve 80% of the usecases anyways

[ozkutuk]

I have been trying my hand at this, but I am not sure how I can go on with interpreting the script. Is compiling to a temporary directory and running it immediately a sensible way to approach this? I couldn't think of any other way, given the options purs executable offers.

[f-f]

The other day in the FP slack I described this feature as "spago repl in a temp folder + adding the script to the sources + spago run". A bit more formally:

For the first iteration I would skip the whole thing about interpreting the shebang in files (as proposed in the first post), and concentrate on getting the following to work:

spago script --tag psc-13.8-sometag -d prelude -d effect myscript.purs

This would:

• create a new project in a temp dir, where we eventually set the package set to the requested one, and eventually pulled the specified dependencies. Note that we have all the machinery to do this for when spago repl is called outside of a project, except for the --tag flag, which is handled in spago init and spago upgrade-set, so it should be easy to pull in
• then we compile this temp project with its normal sources, while adding also the current location of the script to them
• then we call spago run on this temp project, giving the script module (which we could actually fix to Main) as the entry point

Note: it might be very slow to create/download/compile a whole new project for every invocation of spago script. So maybe we can create a local .spago directory that contains a folder for this project (so not a temp one), with a name based on something like "the hash of the parameters passed to the command" (i.e. the set, the dependencies, the script name) so that we can reuse the project on subsequent invocations if only the script changes

@ozkutuk does this make sense?

[ozkutuk]

Sorry for the late response. I have waited until I had a deeper look into the code, but was unable to spare the time required. Despite that, I have understood the approach you describe. I am not working on this for the time being, but I will post an update when I could spare the effort to pick this up again.

[f-f]

@ozkutuk no worries and thank you for the update!

[JordanMartinez]

Just FYI. purescript/purescript#4214 will likely be getting merged soon.