In the last part #2 of the purescript series I got Purescript and it's executable installed, using yarn. Pulp seems to be the default "build system and package manager for PureScript projects" as Bodil Stokke states in her 1st commit to the project. Let me explore it a bit.

After having explored a tiny bit of Purescript in the last post, I want to build stuff now. The book says to install bower and pulp, I just do that a bit different, by using yarn for it and not installing the packages globally.
NOTE: If you still prefer installing it globally, use yarn global instead of yarn for running yarn commands.

> yarn add bower --save
yarn add v0.15.1
# ...snip...
└─ bower@1.8.0
✨  Done in 4.33s.
# ...snip...
> yarn add pulp --save
# ...snip... maaaaany lines (means many dependencies) :)
✨  Done in 6.30s.

I don't worry too much about bower yet, I want to see what pulp can do :).

Pulp - "A build tool for PureScript projects"

As mentioned in the last post, we have ./node_modules/.bin in our PATH, which allows us now to run pulp, which executes the binary located in there. Let's see what pulp has to offer:

> pulp
* Error: Expected command
Usage: pulp [global-options] <command> [command-options]

Global options:
  --before <string>       Run a shell command before the operation begins. Useful with `--watch`, eg. `--watch --before clear`.
  --bower-file -b <file>  Read this bower.json file instead of autodetecting it.
  --else <string>         Run a shell command if an operation finishes. Useful with `--watch`, eg. `--watch --then 'say Done' --else 'say
                          Failed'`
  --help -h               Show this help message.
  --monochrome            Don't colourise log output.
  --then <string>         Run a shell command after the operation finishes successfully. Useful with `--watch`, eg. `--watch --then 'say
                          Done'`
  --version -v            Show current pulp version.
  --watch -w              Watch source directories and re-run command if something changes.

Commands:
  browserify  Produce a deployable bundle using Browserify.
  build       Build the project.
  docs        Generate project documentation.
  init        Generate an example PureScript project.
  login       Obtain and store a token for uploading packages to Pursuit.
  psci        Launch a PureScript REPL configured for the project.
  publish     Publish a previously tagged version to Bower and Pursuit.
  run         Compile and run the project.
  server      Launch a development server.
  test        Run project tests.
  version     Bump and tag a new version in preparation for release.

Use `pulp <command> --help` to learn about command specific options.

I mentioned it in the first post of this series, that Purescript can also be compiled to browser-compatible code, that is what the browserify command will do. Exciting imho. I assume the build command will just build it to commonjs, which I could then use in nodejs. We will see.
I want to try to apply my little knowledge of Purescript on the shell, so I run pulp psci.

> pulp psci
* ERROR: No bower.json found in current or parent directories. Are you in a PureScript project?

Alright, so it might be time to really do pulp init as the book suggests, even pulp version shows this error message. Fine. Convinced. I just wanted to play a little bit :).

> pulp init
* Generating project skeleton in /Users/wk/purescript-series
* ERROR: Found /Users/wk/purescript-series/.gitignore: There's already a project here. Run `pulp init --force` if you're sure you want to overwrite it.

Actually that is true, since I had been playing before and did add this .gitignore file. Ok, so let's force it.

> pulp init --force
* Generating project skeleton in /Users/wk/purescript-series
bower purescript-prelude#*      cached https://github.com/purescript/purescript-prelude.git#2.4.0
bower purescript-prelude#*    validate 2.4.0 against https://github.com/purescript/purescript-prelude.git#*
bower purescript-console#*      cached https://github.com/purescript/purescript-console.git#2.0.0
# ...snip...

diff after pulp init
The diff after `pulp init`
Oh, wow this created some stuff. I was looking at the source code of pulp init and saw that some new files will be created. Instead of going through each of them and pasting all the code here, see the diff (as an image on the left). I see that my Main.purs was overridden by more complex Purescript code. Not sure if I will keep that :). Next the book suggests to write (or paste) a short Purescript script into Main.purs, finally a real hello-world. Yeah.

module Main where

import Control.Monad.Eff.Console

main = log "Hello, World!"

And now I want to see that one running! So pulp run is the right thing. But wait, I will take baby steps, so let me run pulp build before, it should do what I expect, just build the source and do two things:

  1. verify our source code and throw a warning for the missing type annotation and
  2. generate the source code into the output directory.

And it does. The output is verbose and shows what gets compiled and as expected a warning. I already know from the last post that main without a type annotation will give a warning, and it does.

> pulp build
* Building project in /Users/wk/purescript-series
Compiling Data.NaturalTransformation
# ...snip...
Compiling Control.Monad.Eff.Console
Compiling Control.Monad.Eff.Unsafe
Compiling Main
Compiling PSCI.Support
Warning found:
in module Main
at /Users/wk/purescript-series/src/Main.purs line 5, column 1 - line 5, column 12

  No type declaration was provided for the top-level declaration of main.
  It is good practice to provide type declarations as a form of documentation.
  The inferred type of main was:

    forall t1.              
      Eff                   
        ( console :: CONSOLE
        | t1                
        )                   
        Unit                


in value declaration main
# ...snip...
* Build successful.

Confirmed. The compiler complains about main and the missing type declaration. The build succeeded. And the source should have a console.log in it.

> cat output/Main/index.js 
// Generated by psc version 0.10.7
"use strict";
var Control_Monad_Eff_Console = require("../Control.Monad.Eff.Console");
var main = Control_Monad_Eff_Console.log("Hello, World!");
module.exports = {
    main: main
};

And so it does. Awesome. Now just to make confirm, I run pulp run. And it should execute the compiled source.

> pulp run
* Building project in /Users/wk/purescript-series
* Build successful.
Hello, World!

Yep. It printed hello-world. Enough for now. The build tool works and I have seen a proper hello-world.

In the next post I will finally open the REPL and play a little bit with Purescript and afterwards I plan to try out the different building options, such as building it with browserify for a browser compatible JS file.