sato-shi / supervis.es

supervis.es

This is some example code that demonstrates extending the sequence method that is common to functional programming to absorb some monadic abstractions.

Please use Github Issues or comment on Commits to provide feedback. All thoughts are welcome.

yak-shaving

The canonical source code is coffee-src/supervis.es.coffee. The code is tested using npm test, and a pretest script compiles the CoffeeScript to JavaScript in lib/supervis.es.js. jasmine-node then interprets the specs in the spec folder (they're also written in CoffeeScript).

To try it, you'll need node, jasmine-node, CoffeeScript, and their respective dependencies.

code organization

The key function is sequence. In naïve form, sequence appears to create a pipeline through a series of unary functions, much like functional composition in reverse:

plusOne = (n) -> n + 1
double = (n) -> n * 2

sequence(plusOne, double, double)(1)
  #=> 8

If the first argument to sequence is an instance of Supervisor, then sequence will use the Supervisor to wrap and unwrap values along the way. Here is the above example using the Writer monad:

plusOne = (n) -> [n + 1, "(#{n}) -> #{n + 1}; "]
double = (n) -> [n * 2, "(#{n}) -> #{n * 2}; "]

sequence(Supervisor.Writer, plusOne, double, double)(1)
  #=> [ 8, '(1) -> 2; (2) -> 4; (4) -> 8; ' ]

If the first argument isn't a Supervisor instance, sequence actually uses the Identity monad behind the scenes.

At this time, I've coded up:

1. Identity
2. Maybe
3. Writer
4. List
5. Promise
6. Callback

The Promise monad wraps a ridiculously simple Promise implementation. Errors fall through much like the Maybe monad. Callback is an implementation of Haskell's infamous "Continuation" monad: You can sequence asynchronous callback functions without ugly nesting.

feedback wanted

Yes please!

• File a Github Issue
• Comment on a Commit
• Fork this and issue a Pull Request

Thanks!