Algebrick - Algebraic types and pattern matching for Ruby

14 May 2013 Tags:

I've just released a new gem algebrick which brings algebraic types and pattern matching to Ruby. It's not as powerfull as Haskell's but it can still be quite useful. Let me give you a quick taste of the syntax.

Quick example

Load DSL for type definition and define some algebraic types

extend Algebrick::DSL

type_def do
  tree === empty | leaf(Integer) | node(tree, tree)
end

Now types Tree(Empty | Leaf | Node), Empty, Leaf(Integer) and Node(Tree, Tree) are defined. Lets add some methods, don't miss the pattern matching example.

module Tree
  # compute depth of a tree
  def depth
    match self,
          Empty >> 0,
          Leaf >> 1,
          # ~ will store and pass matched parts to variables left and right
          Node.(~any, ~any) --> left, right do
            1 + [left.depth, right.depth].max
          end
  end
end

Methods are defined on all values of type Tree

Empty.depth                                        # => 0
Leaf[10].depth                                     # => 1
Node[Leaf[4], Empty].depth                         # => 2
Node[Empty, Node[Leaf[1], Empty]].depth            # => 3

Do you wish to know more?