multifun

Clojure-inspired multimethods for JavaScript.

Why?

Problem statement: JavaScript does not offer native constructs to facilitate the orchestration of functions.

Say we need to generate code that greets someone in a given programming language:

greetings('clojure', 'John');
//=> '(print "Hi John!")'

greetings('shell', 'John');
//=> 'echo "Hi John!"'

Here's one classic implementation:

const greetings = (lang, name) => {
  switch (lang) {
    case CLOJURE:
      return greetings_clojure(name);
    case SHELL:
      return greetings_shell(name);
    default:
      throw new Error(`unknown: ${lang}`);
  }
};

Let's take a moment to identify the important bits:

1. We need some parameters (pink)
2. We need a dispatch value to make a decision (yellow)
3. We need a "decision tree" (green)
4. We need a fallback (orange)

Everything else is just implementation details....

It is these details that multifun intends to manage so that you can focus on what matters the most:

How does it work?

const multifun = require('@customcommander/multifun');

const xyz =
  multifun
    ( dispatching_fn
    , 'xxx', handle_xxx_fn
    , 'yyy', handle_yyy_fn
    , 'zzz', handle_zzz_fn
    // ...
    , fallback_fn
    );

xyz(...);

Here are the parameters to multifun:

1. The 1st parameter is the dispatching function. It takes all the parameters passed to xyz and returns a value.

2. Then you have a serie of value & handler pairs. If a value is strictly equal to the dispatched value, its handler is applied to the parameters passed to xyz. (No other pairs will be evaluated.)

3. And finally a fallback function if no values matched. It is applied to the parameters passed to xyz.