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.
• icu - libicu is used for locale-aware case conversions.

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

Development

Running the tests

To run all tests, run npm run test. This will run both the scheme runtime unit tests and the snapshot tests.

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 cd test-snapshots && spago install <packages...>.

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))
>