@transformation

Communicating Sequential Processes introduced by Tony Hoare is great way of thinking about structuring concurrent problems. If you are curious Rob Pike explains the concept very well in this video:

While Communicating Sequence Processes (CSP) is a very powerful paradigm, it is also a bit daunting and verbose for simple programs. Especially there is a very interesting class of programs that just takes input, executes a series of steps and transformations and outputs the data again. There are numerous examples of the relevance of this class of programs, Unix pipelines, stream processing like RxJS or even just a sequential program.

One of the big benefits of CSP is that you can control the buffering of channel between sub-processes, this gives you back presure and declarative concurrency out of the box. So compared to normal streaming libraries, you can create composable building block and control the concurrency from the consumer.

This collection of libraries seek to build an extensive toolkit of processing steps, that can be composed into processing pipelines.

Packages

• @transformation/core - the core API that everything builds on top of.
• @transformation/csv - read and write CSV files.
• @transformation/ejs - write files with EJS templates.
• @transformation/file - read and write files.
• @transformation/glob - find files using glob patterns.
• @transformation/process - work with child processes.
• @transformation/stream - integrate with Node streams.

Changelog

Example

Let's try to make a small program that prints packages in this project has a local dependency on another package.

• glob search for all package.json files in the packages directory
• read the content of each of the package.json files in parallel
• parse the content as JSON
• extend the structure with a new field: localDependencies, that is containing dependencies starting with @transformation/
• filter out packages that don't have local dependencies
• print out the result

const fs = require("fs").promises;

const { glob } = require("./packages/glob");

const {
  extend,
  filter,
  map,
  parallel,
  program,
  tap,
} = require("./packages/core");

const main = async () => {
  await program(
    glob("./packages/*/package.json"),
    parallel(map(fs.readFile), 4),
    map(JSON.parse),
    extend({
      localDependencies: map(({ dependencies }) =>
        Object.keys(dependencies).filter((dependency) =>
          dependency.startsWith("@transformation/")
        )
      ),
    }),
    filter(({ localDependencies }) => localDependencies.length > 0),
    tap(
      ({ name, localDependencies }) =>
        `${name} => ${localDependencies.join(", ")}`
    )
  );
};

main();

You can also take a look at these tools that uses this library:

• workspace-cache
• offline-github-changelog

Acknowledgment

The library is build on top of a very nice CSP library called medium.

MIT License

Copyright (c) 2020 Sune Simonsen mailto:sune@we-knowhow.dk

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.