Update Chapter 2 - Testing Code Using the Interactive Mode

[p2327]

After following the step up to the secion Testing Code Using the Interactive Mode, executing
$ spago repl will throw:

purs repl: PSCi requires the psci-support package.
For help getting started, visit https://github.com/purescript/documentation/blob/master/guides/PSCi.md
spago: callCommand: purs repl ".spago/console/v4.4.0/src/**/*.purs" ".spago/effect/v2.0.1/src/**/*.purs" ".spago/prelude/v4.1.1/src/**/*.purs" ".spago/psci-support/v4.0.0/src/**/*.purs" "src/**/*.purs" "test/**/*.purs"  (exit 1): failed

Please add current instructions to load the psci-support package, like so:

spago install psci-support

This code was written on MacOSX Mojave 10.14.6 using:

• spago==v0.14.0.0
• purs==v0.13.6
• npm==6.14.4

[hdgarrood]

This is strange - an explicit spago install psci-support shouldn't be necessary, especially since psci-support already appears to be listed in the dependencies section in exercises/chapter2/spago.dhall.

[JordanMartinez]

So, funnily enough, if one just runs spago repl in a directory that doesn't have a spago.dhall file in it, this will work fine.

However, if one runs spago init and then spago repl, it will produce this error because a spago install was never ran. Thus, while it may be listed as a dependency, psci-support is never installed into that local folder, so that spago repl can function correctly.

[hdgarrood]

Interesting, good find! Perhaps spago repl should ensure that all dependencies are installed before attempting to start the repl, then?

[JordanMartinez]

It should only if a spago.dhall file exists in the directory in which it runs. Otherwise, it should work as it currently does when there isn't such a file.

[JordanMartinez]

There's already an issue for this, but it doesn't quite address this particular problem: purescript/spago#550

[hdgarrood]

I opened purescript/spago#611

[hdgarrood]

This is apparently a bug in spago which should be fixed as of the next release.

[JordanMartinez]

This bug no longer appears if one uses Spago v0.15.2.

To close this, we should update the repo to use that version of Spago in its instructions. However, the Spago release is a breaking change, so I don't know whether that would be problematic in other areas.

[hdgarrood]

The only breaking change is the removal of an obscure CLI flag which I doubt this repo was using, so I think updating will be fine.

[milesfrain]

To close this, we should update the repo to use that version of Spago in its instructions.

Do we need to specify specific tool versions?
Any reader who runs the suggested:

npm install -g spago

will get the latest version (0.15.2 currently).

https://book.purescript.org/chapter2.html#installing-tools

[hdgarrood]

Yeah, I'd be tempted to just leave this. I think asking people to try updating their tools if things go wrong is the correct approach in general.

[JordanMartinez]

Do we need to specify specific tool versions?

At one point, I didn't specify the version of tools in my learning repo. Then, breaking releases were made that messed up a number of the commands I listed. So, I think it's better to list a specific tool version. That way, one can ensure that entire repo is updated before upgrading.

However, some tools (e.g. Spago) are more mature now than when I made that decision. So, I don't know whether that's really desirable at this point either.

Regardless, I don't think we should specify tool versions until it becomes an issue.