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Who Am I

Tim Washington
Software Developer - InterruptSoftware.ca

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My Progression

OO
Design Patterns
Language Design
Functional Programming

Guiding Principle: maximize expressive power

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Concept of Computation

What does it mean to compute?

Me: to compute is an actualization (or concrete version) of a mathematical function.

Alan Turing: his ideas of computation can be found in

his contributions to the concept of an algorithm and
his description of a turing machine

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Algorithm

An algorithm is just a step-by-step procedure for calculations.
Those steps are expressed as a finite list of well-defined instructions for calculating a function.

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Turing Machine (a gross simplification)

A theoretical computer, that

i) consumes an infinite ribbon of tape and
ii) can perform read and write operations on the tape and
iii) alters its own state

The concept is that a Turing machine can calculate anything that is computable, no matter the complexity (ie. anything for which there is a function).

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Let's look at 2 programming models and how they address the question of how we should go about computing...

Object-Oriented Languages
Lisp

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OBJECT-ORIENTED

OO is actually a programming paradigm, based on what Alan Kay called the "Actors Model"

1. Everything Is An Object.
2. Objects communicate by sending and receiving messages
3. Objects have their own memory
4. Every object is an instance of a class
5. The class holds the shared behavior for its instances
6. To eval a program list, control is passed to the first object and the remainder is treated as its message.

This definition is derived from early versions of Smalltalk. Rule 6 shows Smalltalk's Lisp heritage

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LISP

1. Code is Data. You can think of your source file as an AST that gets loaded into the running system.
2. Functions is a first class object
3. Recursion

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Bookkeeping System in Java (OO)

XML / Java binding framework
XPath module
Language Design
Custom DSL implementation
Custom Shell to run language implementation

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Bringing in Clojure (LISP)

s-expressions (code is data) meant I didn't need XML as an extra data transfer language between my systems

XML / Java binding framework
XPath module

functions and macros removed need for a separate DSL and library

Language Design
Custom DSL implementation
Custom Shell to run language implementation

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Other Benefits

Much smaller code size

clojure syntax
immutable data
lazy evaluation
dynamic typing
concurrency primitives

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