macros.coffee

Down-and-dirty, 100-line (cake loc shows 87, actually) implementation of Lisp-style macros for CoffeeScript. Annotated Source

You can install it like so:

npm install macros.coffee

And then require() it before requiring any file(s) that use macros:

require "macros.coffee"
app = require "my_application_that_uses_macros" 

app.start()

Or, to compile to javascript files from the command line (currently very flaky):

$ macros.coffee app/*.coffee

Examples

Some examples can be seen in the /test directory. Use of quote, backquote, macro-defining-macros, call-with-current-callback (cc()) ...

Writing Macros

Macros are functions that operate on nodes of a program's Abstract Syntax Tree (AST). Here's a basic macro.

mac foo (nodes)->
  CoffeeScript.nodes "x = 2"

foo() becomes x = 2;.

More complex or messy macros may want access to two other arguments that are passed in every macro: the parent node, and the global Macros object containing all of the macro definitions.

Basic Macro Tools: Quote, Backquote and Gensyms

A macro that replaces occurrences of x with a 2:

mac two_for_x (n)->
  backquote (x:2), n

two_for_x( y = x ) # produces y = 2

Backquote is a function that performs the implied replacement on an AST. Quote, on the other hand, is a macro, not a function because it needs to do this:

node1 = quote -> 2 + 2
node2 = CoffeeScript.nodes "2+2"
node1.compile() is node2.compile()

Here's a useless example that assigns x, y, and z to a value:

mac assign_xyz ({args:[val,rest...]})->
  backquote {val:val}, quote ->
    x = y = z = val

assign_xyz 12

... why???

I wrote this because I really, REALLY wanted to write macros in CoffeeScript. In Ruby, the buy-in to message-passing goes deep, and you can override most of the language, but in JS/CS metaprogramming is limited to tricks on this.

If you want to fork this and make it better, or build a substantially more 'heavy-duty' implementation, I'll probably end up using yours.