rubyhs/doc/presentation.org

* Introduction
Write a static analyzer for ruby.

Used an existing parser for ruby called `ruby-parse`.

`ruby-parse` can generate an AST in JSON format.

This made the task of writing a ruby parser simpler: Haskell comes
with a great JSON parser.  So we just have to specify how to convert
from the AST defined by `ruby-parse` to our own AST.

* Implementation
** ADTs
*** Purpose
Defining an Abstract Syntax Tree (AST) for Ruby using Algebraic Data
Types (ADTs).

*** Example
    -- Value represents any JSON data (object, string, number, null, array)
    Args       = Value
    Name       = Value
    Block      = [Definition]
    Definition = Module | Function | Send
    Namespace  = [Name]
    Send       = {args : Args, namespace : Namespace, name :: Name}
    Module     = {name : Name, block : Block}
    Function   = {name : Name, args : Args, block :: Block}

*** Live coding

Define `Function`
** Higher-order types
Missing a good example here.

** Type classes
*** Purpose
Be able to concert unstructured JSON data into our ADT.

*** Example
Consider the class

   class FromJSON a where
     parseJSON :: Value -> Parser a

It's saying that `a` is convertible from json if there is a function
`parseJSON` that takes a (json) `Value` and returns a `Parser a`.
`Parser a` can be thought of as a procedure for generating a value of
type `a`.

So for instance.  The monomorphic type `Parser Function` is a
procedure that generates a value of type `Function`:
*** Live coding
Define an instance for `FromJSON` for `Function`.

Define an instance for `FromJSON` for `Definition`.