Lisp ERP

Get Hy with Tryton

Today I am going to talk about developing modules in Tryton using a dialect of Lisp called Hy.

I will talk a bit about Lisp.
I'll try to explain why Lisp.
We will see what Hy feels like.
Finally we will see how to write modules in Hy for Tryton.

I am guessing that many people her programs in python.

How many of you program in more than one programming language?

Do you prefer a language over another?

I do I like dialect of Lisp and even within the dialects I've one that I like best.

It’s been years since I moved as much as possible away for java and javacript in favour of clojure and clojurescript the lisp alternatives to them. I knew there was no clojure for python and even if there was it would had been an uphill battle, but hy is not clojure. Hy as I will explain it is very python while clojure is almost zero javanish.

I didn’t choose tryton because python. I didn’t come to Tryton thinking that I may be able program in a Lisp dialect even though I really really really like Lisps and in particular I love clojure. I really thought that I would had to learn python and live a bit of a pythonic life. In fact the first module that I wrote was and still is written in python. Finding out that I could write most of the code of my tryton modules in Lisp made me a very happy developer. I love Lisp and I feel very fortunate that I can program with Hy while developing modules in Tryton. I still live a minor pythonic life though Hy and reading Tryon’s code.

Tryton Rocks

local support
open source / org / foundation
community
tech: architecture, postgres, scenarios, testing, …

My path to Lisp

What's this thing?

AI course

I want it

Paul Graham - Hackers and painters 2005
Abelson & Sussman SICP lectures and book

Yes I can!

Rich Hickey - Clojure

Lisp?

By John McCarthy 1958ish at MIT.
Lisp : family of programming languages.
Flavors. Common Lisp, Scheme, Racket…
Functional. Dynamic. Garbage Collected. Code-as-data. REPL…

New Flavors of Lisp

Java 1995 -> Clojure 2007'
Erlang 1986 -> LFE 2008
Javascript 1995 -> Clojurescript (cljs) 2011'
Python 1990 -> Hy 2013'

Clojure for JVM vs Hy for Python

Clojure Hosted (not Javaistic)

"Clojure is a robust, practical, and fast programming language with a set of useful features that together form a simple, coherent, and powerful tool."

dynamic
own data structure
control mutation/state
…

Hy Embedded (Pythonistic)

"Hy is a wonderful dialect of Lisp that’s embedded in Python."

"Since Hy transforms its Lisp code into the Python Abstract Syntax Tree, you have the whole beautiful world of Python at your fingertips, in Lisp form!"

Python data structures
Python truthiness

What's special about Lisp?

S-expression
simple syntax
infx notation
code-as-data - meta-programming

(operation operant1 op2 …)

(+ 1 2 3)
(if (event? 2) "yes" "what?")
(= 1 2)
(defn inc2 [x] (+ 2 x))

(((((())))))

buy one get two
print('hello') -> (print "hello")

Test hy

Hy Tryton Modules

pip install hy
create a module
__init__.py (as usual + import hy)
Write hylang files .hy files instead of python.
You still have to write the same xml files :)

Let's look at some code.

hello.hy

(import [trytond.model [ModelSQL ModelView fields]])

(defclass Hello [ModelSQL ModelView]
  "Hello World"
  [--name-- "hello"
   name (.Char fields "Name" :required True)
   greeting (.Function fields
                       (.Char fields "Greeting")
                       "get_greeting")]

  (defn get-greeting [self name]
    (.format "Hello {}" self.name)))

Example macro default

@classmethod
def default_company(cls):
    return Transaction().context.get('company')

(with-decorator classmethod
   (defn default-company [cls]
      (.get (. (Transaction) context) "company")))

(default company
    (.get (. (Transaction) context) "company"))

Macro source

(defn default-func-name [name]
  (+ "default_" (.replace name "-" "_")))

(defmacro default [field args &rest body]
  `(with-decorator classmethod
     (defn ~(HySymbol (default-func-name (name field)))
       ~(+ [(HySymbol "cls")] args) ~@body)))