Macros Without Parentheses

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.x6[ Macros ] .x3[Without] .huge[ Parentheses ]

Luc Fueston

slides linked from post on

### mrluc.github.com

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## I'm from .x2[MN]

## But I live half of each year in .lg[South America.]

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### No waves = .x2[Lisp-style macros] for .x2[CoffeeScript] .sm[in < 100 lines]

![ hammock driven development ](./img/ecu_code.jpg)

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# Not because I'm a wise Lisp Greybeard.

# Because it's fun, and

## I ♥ Ruby and CoffeeScript, and .x2[macros are what you miss about Lisp.]

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# Not because I'm a wise Lisp Greybeard.

# Because it's fun, and

## I ♥ Ruby and CoffeeScript, and .x2[macros are what you miss about Lisp.]

.center.x2[ `.lisp (setf x 4)` ]

.x4[ When you inevitably] .x6[ leave. ]

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# 1. What are macros?

# 2. Introducing macros.coffee

# 3. The view from Ruby

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macros are

# Named AST transforms

non-snarky reminder:

# String -> Tokens -> AST

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# So, if you want macros.

## What do you do to the AST?

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# Do Two Things to the AST

![Macro Stage Visualized](img/macros_diagram.png)

## Find and compile named definitions

## Apply definitions to calls

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# So, once you have macros.

## What do you do with them?

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# 1. Domain Specific Languages

# 2. Control Flow

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# Domain-Specific Languages

Macros can be used for the same purpose as macro methods.

.ruby
    obj = fighter do
      acts_like :beserker
      
      attack do
        flail_wildly
      do
    end

# if Ruby had macros, might compile to: 
    obj = Fighter.new.instance_exec { 
      include get_behavior_module(:beserker) 
      
      def attack() 
        super @enemy, :flail_wildly 
      end
      self
    }

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# Control Flow Though Experiment

## Compile-time > run-time for control structures.

def iif(cond, ok, notok) 
      if cond 
        ok.call()            # slowness d'oh!
      else 
        notok.call()         # slowness d'oh!
      end 
    end

iif 2 > 1, 
      ->{ p "success!"},     # user d'oh!
      ->{ p "humbuggery!"}   # user d'oh!

# and 2 lambdas per 'elseif'

## Macros have no inherent runtime penalty.

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# Know what you want to say?

# Know what you want it to mean?

# Both expressions parse?

# .x2[Macros can do that.]

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in coffeescript

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.lg[macros.coffee is]

#### a straightforward implementation that works as described

![Macro Stage Visualized](img/macros_diagram.png)

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## .center.x2[ Not a fork]
# .center[ Wraps CoffeeScript, does two things ]

nodes: (str, strict=@strict)=>

@ast = CoffeeScript.nodes str

if !strict or uses_macros(@ast) 
                
        @find_and_compile_macros()           #1 definitions

@macroexpand() until @all_expanded() #2 calls

@ast

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87 lines

Annotated source with Docco

![docco](img/implementation.jpg)

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.x2[`npm install macros.coffee`]

Boy, it would be embarrassing if that didn't work right now.

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# Require it, then require files with macros

## No macros in the entry file

require 'macros.coffee'
    app = require 'my-app' #now it hooks nodejs require()
    
    app.start()

## Declaration in files with macros

.coffeescript
    'use macros'

mac instant_2_plus_2 (n)->
      backquote {z:2}, quote ->
        z + z
    
    instant_2_plus_2()

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# Namespaces are coming (easy)

## They'll be declarations too:

.x2[ `.ruby 'use macros.name'` ]

.x2[ `.ruby 'in macros.name'` ]

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Debugging is ... interesting.

Compiling works, but is meh.

jashenkas could break AST deepcopy with a single well-placed closure

don't have a 'vision' yet for lots of biggish questions.

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# what good is it?

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if you're doing:

### language experiments
### ast mangling (control flow)

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## .center[ QUIZ ]

x = 37

x for x in [1..10]

console.log x

(a) `.coffeescript x is 37`

(b) `.coffeescript x is 10`

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## .center[ QUIZ ]

x = 37

x for x in [1..10]

console.log x

<s> (a) `.coffeescript x is 37` </s>

<s> (b) `.coffeescript x is 10` </s>

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# gensyms to the rescue
## 'para': list comprehensions in spanish

.coffeescript
    x = 37
    para .hl[x] en [1..10] si (.hl[x] > 3) hazte eso pues -> .hl[x]
    x is 37

inside the loop

.javascript
 for (_i = 0, _len = _ref.length; _i < _len; _i++) {
 .hl[x_g9] = _ref[_i];
 if (.hl[x_g9] > 3) {
 .hl[x_g9];

}
    }

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# async control flow

.coffeescript
    if x = async_fn .hl[cc()]
      p x
    else
      p "Onoz"

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## `cc` is a 20-line macro

.javascript
    agreet(function(__thang) {
      var x;
      if (x = __thang) {
        p(x);
      } else {
        p('Ohnoz');
      }
    });

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# If you mangle the AST,

# why not use an abstraction built for it?

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# Closure.

# Compilation.

## two abstractions that work great together

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# Macros only work in:

- Lisps and '()-like languages, including Clojure

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# Macros only work in:

- Lisps and '()-like languages, including Clojure
- MetaLua
- Potion (_why's language)
- __Factor__
- __Julia__
- others

## Languages where macros turned out to be a mistake:

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# Macros only work in:

- Lisps and '()-like languages, including Clojure
- MetaLua
- Potion (_why's language)
- __Factor__
- __Julia__
- others

## Languages where macros turned out to be a mistake:

- Maybe CoffeeScript, now.

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# Ruby Issues

- _RubyMacros_ - real macros

- use a special require
  - requires RedParse
  - about 2 years old

- _rbx transforms_ - GoGaRuCo 2011 lightning talk on this. Yehuda seems interested in them.

- Rubinius only
  - no one has written actual macros yet
  - but you could totally do it

- __Ruby needs canonical representation.__

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# Books on Macros

## Free

- _On Lisp_ - pg

- _Let Over Lambda_ - Hoyte

## Non-free

- _PAIP_ - Norvig

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no way there's time for

# .x2[ Questions? ]

superluc@gmail.com

github.com/mrluc/macros.coffee
 
Thanks Ruby.mn ♥