1. CPSC 311: Definitions of Programming Languages
Instructor: Steven Wolfman
(and this is one of the only sets of slides you'll see all term!)
Welcome to CPSC 311, where we'll metaphorically dig our hands into the metaphorical guts of programming languages!
But first, what's the most common security flaw in a program?

2. Digression: Security Once upon a time...
...buffer overflows were the most common security vulnerability in programs.
Can you overflow an array in Java?
If yes: how?
If no: why not?
Image from Wikipedia article on buffer overflows.

3. Digression: Security And now...
...cross-site scripting (a type of code injection, not in SQL and less funny) vulnerabilities are the most common security vulnerability in programs.
How should we protect against these?
xkcd.org
Facebook was running into these kinds of problems and other related straightforward bugs.
Show example from FaceBook talk. Turns code like:
$div =
'<div id="console" class="consoleLog">'.
htmlspecialchars($logEntry).
'</div>';
Into code more like:
<div id="console" class="consoleLog">
{$logEntry}
</div>;
Facebook
XHP (among other things)

4. Outline Why should you care about this course?
How will this course work?
Why Racket?
How are Scheme and Racket related?
Why Scheme/Racket?
Start learning Racket

5. Why should you care about this course?
Programming languages are the key tools that define how we think about computations, and what we're able to create.
What you learn during this course will give you the power to learn, choose, and craft your tools effectively.

6. How would you draw this picture ...
... using a computer?
Source Code
Compiler
Object Code
(Running example from “Little Languages” by Jon Bentley.)

7. Which way is better? Slideware, graphics library, or... Source Code
Compiler
Object Code
Describe using the PIC language, and compile:
ellipse “Source” “Code”
arrow
box “Compiler”
ellipse “Object” “Code”
PIC is a “domain specific” language for describing pictures.

8. Which way is better?
What if the picture you wanted to draw looks like this ?

9. Which way is better?
What if the picture you wanted to draw looks like this ?
PIC description of this picture:
pi = ; n = 10; r = .5
s = 2*pi/n
for i = 1 to n-1 do {
for j = i + 1 to n do {
line from r*cos(s*i), r*sin(s*i)
to r*cos(s*j), r*sin(s*j) }

10. Which way is better? A C program that draws the same picture:
#include “graphics.h” // A graphics library
main() {
double pi = ; int n = 10;
double r = 0.5;
double s = 2*pi/n;
for (int i = 1; i<=n-1; i++)
for j = i + 1; j<=n; j++)
line(r*cos(s*i), r*sin(s*i),
r*cos(s*j), r*sin(s*j) ); }

11. Three Ways to Describe a Picture
Use a Picture Drawing program like PowerPoint.
Use a Special “Domain Specific” Picture Language
Use a General Purpose Programming Language and a “Graphics Library”.
Which is “best” under what circumstances and why?

12. Another example...
What if the picture you wanted to draw looks like this ?

13. The CHEM Language CHEM = “Molecule Picture” Language
special constructs for this specific purpose
compiled to PIC code
Excerpt from picture's CHEM description:
R1: ring4 pointing 45 put N at 2
doublebond -135 from R1.V3 ; O
backbond up from R1.V1 ; H
frontbond -45 from R1.V4; N
H above N
bond left from N ; C
...

14. How PIC is Implemented PIC input TROFF PostScript Lexical Analysis
Syntax Analysis
Code Generation
TROFF
Print
PostScript

15. How PIC is Implemented “Little” Languages Everywhere! PIC input
PIC Language
Lexical Analysis
Syntax Analysis
Code Generation
TROFF
TROFF Language
Print
PostScript
PostScript Language

16. How PIC is Implemented “Little” Languages Everywhere! PIC input
PIC Language
Lexical Analysis
Lexer C Code
LEX Tool
Lex input
Lex Language
Syntax Analysis
Compile
Parser C Code
YACC Tool
Yacc input
Yacc Language
Code Generation
Code Gen
C Code
TROFF
TROFF Language
Print
PostScript
PostScript Language

17. Outline Why should you care about this course?
How will this course work?
Why Racket?
How are Scheme and Racket related?
Why Scheme/Racket?
Start learning Racket

18. Definition of Programming Languages
We'll study programming languages:
how they work
how they let us say the things they let us say
what different design features languages can have
how those features fit together

19. Approach
1. Play with programs that exploit some language design choice.
2. Deeply explore the choice by building an interpreter that executes the language (defining an “interpreter semantics”).
3. Ask questions like: How would programmers perceive/use these design choices differently? How are they defined differently in the interpreter?
4. Tinker with the language and interpreter.
And.. repeat!

20. Outline Why should you care about this course?
How will this course work?
Why Racket?
How are Scheme and Racket related?
Why Scheme/Racket?
Start learning Racket

21. Racket's plai module
plai is a module (a “#lang option”) in Racket that supports several useful structures for building interpreters.
Racket is a rich and flexible (and compatible) extension of Scheme.
Scheme is a simple, elegant, yet extremely powerful language uniquely suited to “interpreter semantics”.
So we have to learn plai. Let's get started!