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Frederik Hanghøj Iversen 2019-10-11 16:28:19 +02:00
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* 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`.