20 августа: DSL и макросы

from_macro.n

macro @from (start, end, body)
syntax ("from", start, "to", end, body) {
    System.Console.WriteLine("Compiling from...");
    <[
        for (mutable i = $start; i <= $end; i++) $body
    ]>
}

from_usage.n

using System.Console;

mutable i = 10;
from 3 to 5 {
    i--;
    WriteLine("hello");
}

pattern_matching.n

def a = 1;
def b = 2;
def pair = (b, a);
match (pair) {
    | (1, 1) => WriteLine("one in both");
    | (1, _) => WriteLine("one in first");
    | (x, 1) => WriteLine("one in second; first: " + x.ToString());
    | _ => WriteLine("no ones");
}

turtle_dsl.rb

class Turtle
  def initialize(&block)
    @x = 0
    @y = 0
    instance_eval &block if block_given?
  end

  def up
    @y -= 1
  end

  def down
    @y += 1
  end

  def left
    @x -= 1
  end

  def right
    @x += 1
  end

  def start(action)
    puts "turtle is #{action} at (#{@x},#{@y})"
  end
end


Turtle.new do
  up
  start :singing
  down
  3.times { left }
  start :dancing
  2.times { down }
end