A javascript based morph
JavaScript Perl
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A javascript based morph.

What is morph?

Morph is a language and an idea of building language bottom-up with specially designed bottom-up extensible grammar. In other words it's a generalization of Lisps macros and Perl 6 mutable grammar.

Why Javascript?

  • it's high level
  • it's popular
  • it has good implementation
  • it has obvious language flaws
  • I like it


Javascripts for-in loop has a well-known flaw - it can iterate by ad-hoc inherited properties. The usual solution is wrapping loop body with obj.hasOwnProperty(key) which is annoying. How cool would be writing it like:

for (own key in obj) {
    // do something with own properties of obj

And you can do it in sky, by just adding a rule like:

rule ~ for (own <key:ident> in <object:expr>) <code-block> ~ {
    var temp = uniq_ident();
    return ~
        var <temp> = <object>;
        for (<key> in <temp>) {
            if (<temp>.hasOwnProperty(<key>))

Rules can help fix language flaws, avoid design pattern copy-paste, make DSLs. You can even morph one language into another and use them together.


Lots of things, actually. Most urgent are:

  • support repeat in rules
  • file scope for rules
  • lexical scope for rules
  • some compiler
  • make it usable

More distant ones:

  • morph Javascript into Javascript
  • fix well-known language flaws
  • morph CoffeeScript into Javascript
  • enable in-browser usage

Compiling strategies:

  • stay near the core, use target language types and their methods.
  • use wrappers for types, with custom behavior and methods.

The first one is simpler and will result in faster code. Second permits new types, operator overloading and such and will probably require optimization. Also, since we wrap a lower level target makes sense. Some smart optimizations such as defining what type is wrapped at compile time or generating several versions for different types will be useful.