purescm

purescm - Chez Scheme backend for PureScript

Installation

Install requisites:

• chezscheme - you should have the scheme command available in your $PATH.
• libpcre2 - purescm has a runtime dependency on the 16-bit variant of pcre2. Check your package manager for pcre2 or pcre2-16 or similar.

You can install purescm with npm:

npm i --global purescm

Usage

The best way to use purescm is to use the spago integration for alternative PureScript backends. In spago.yaml use the backend config like so:

workspace:
  backend:
    cmd: purescm
    args:
      - "build"

Then to compile your purescm project you can run:

spago build

This will produce output under output/. You can run the compiled program with:

purescm run

Bundling

Scheme files can be precompiled to a single Chez program:

purescm bundle-app

which generates a single file output/main which can be run with scheme or petite:

scheme --program output/main

Vendored Dependencies

In order to represent Array and record types in purescm, the backend has a runtime dependency on implementation of SRFI 214 (Flexvectors). This is due in part to how vectors are more like "arrays" than "array lists".

We vendor chez-srfi using the following steps:

1. Clone chez-srfi at the project root.

2. Navigate to chez-srfi and run ./install.chezscheme.sps ../vendor. This should produce an srfi folder inside of vendor.

3. Copy the desired SRFIs from vendor/srfi into vendor/purs/runtime/srfi. Make sure to also copy the SRFIs and other scheme files (e.g. the ones in the private folder) that they depend on. The library-requirements function can aid in this process.

4. Modify the copied scheme files such that the library names align with the folder structure. sd makes this easy!

sd "\(srfi " "(purs runtime srfi " vendor/purs/**/*.sls

5. To verify, simply invoke the Scheme REPL:

$ scheme --libdirs ./vendor:
Chez Scheme Version 9.5.8
Copyright 1984-2022 Cisco Systems, Inc.

> (import (purs runtime srfi :125))
>

Snapshots

To run snapshots, run npm run test. To overwrite old snapshots with the latest output, run npm run test -- -a "--accept". To add a new snapshot, create a file called Snapshot.X.purs where X indicates what is being tested. If a snapshot needs a dependency, install it by running spago -x test-snapshots/spago.dhall install <packages...>. The snapshots have their own spago.dhall file so as not to pollute the purescm binary with unneeded dependencies.