Show HN: multimethod.js - a Clojure-inspired multimethod library for JavaScript

by KrisJordan • 15 years ago

49 10 15 years ago

cfontes• 15 years ago

Nice stuff, I liked the approach.

But what is the benchmark for this kind of structure against regular JS workflow? I guess it will be slower, but how much ?

KrisJordan3• 15 years ago

Good question.

Performance will depend on a number of factors, such as how complex your dispatch function is, how complex your dispatched values and match values are (deep equality becomes more expensive as the compared objects grow in complexity), and how many methods are registered. In general, it is much more expensive than native switch statements or prototype chain lookups.

If performance is of utmost importance and you can substitute a switch statement or prototype hierarchy for a multimethod, you should. Multimethods are a useful pattern for achieving things that either aren't possible in switch (add/remove cases dynamically, deep equality case matching) or are not naturally/painlessly expressed with a prototype hierarchy.

swannodette2• 15 years ago

It doesn't have to be any slower than highly optimized switch statements if you're willing to compile to JavaScript. All you need analysis / compilation support. I've been working on this for a while now for Clojure / ClojureScript.

brian_c• 15 years ago

Neat! I made something (I think) similar a while back, also inspired by Clojure. Mine's more of a proof-of-concept, as I have zero Clojure experience outside some very casual reading.

https://github.com/brian-c/patterned-function

hyperturtle• 15 years ago

I like this very much. It's like a lightweight dispatcher/router/alternative to tons of switches/if & elses. And also that the source is very short and readable.

gerggerg2• 15 years ago

in coffeescript:

    fib = (n) -> switch n
      when 0 then 0
      when 1 then 1
      else fib(n-1) + fib(n-2)

    alert fib 20

KrisJordan3• 15 years ago

While fib is a good example of concisely illustrating the control flow of a multimethod, it is a bad example of where it makes sense to use a multimethod. What is interesting about a multimethod is you can change your dispatch logic and bind new cases well after your multimethod function is constructed. In situations like fib where you know every case you need to handle up front you should certainly use 'switch'.

To illustrate this flexibility in the context of fib, multimethod.js, and CoffeeScript:

   > fib = multimethod()
           .when(0, 0)
           .when(1, 1)
           .default (n) -> fib(n)
   > fib 20
   6765

   > fib.dispatch (n) -> n.numberVal or n
   > fib 20
   6765

   > fib { numberVal: 20 }
   6765

   > fib.when 2, 1
   > fib.when 3, 2
   > fib 20
   6765 (now "optimized" with fewer recursive calls than before)

gerggerg2• 15 years ago

Could you comment on a good use-case for this? A time when it would actually be better to construct a switch block dynamically vs all at once.

Show HN: multimethod.js - a Clojure-inspired multimethod library for JavaScript

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