* introduction

** How does PostScript relate to other languages?
Introduce parts of the language by comparing PostScript to other languages. 

*** Forth
**** Similarities
stack based

separate execution, paramater, and environment stack

They both read in text, build up data structures in memory, and
interpret the data structures.

**** Differences
Forth binding is at compile time.
PostScript binding is at run time and scan time (autobind).

Forth compiler (outer interpreter) reads in text and builds up functions
out of pointers to other functions, and in-line literals.
The compiler is built into the language, extensible by the user. 

The Forth interpreter (inner interpreter) threads through compiled
Forth code by dereferencing pointers until it reaches executable code.
The causal (sic) user does not modify the inner interpreter.

The PostScript scanner reads in text and builds up data structures that
represent code, variables, and the environment, which the interpreter
executes. You can't modify the PostScript scanner.
But you can write your own data structure interpreters.

Forth does no type checking at run time. The only things on the stack
are 16 bit (or 32 bit, or whatever) numbers. Forth functions can't
find out what type their arguments are by looking, they assume the
things on the stack are of the type they're expecting.  You write
different functions to handle for different types.

Each PostScript object on the stack (or anywhere else) has a type.
The stack is 64 bits wide, and each object includes type information,
and either an atomic object (number, boolean, null, etc), or a pointer
to the object body (array, file, string, etc). PostScript functions
can be polymorphic. They can tell the type of the objects on the
stack, so you can write functions that handle different types of
arguments. 

*** Lisp
**** Similarities
dynamic binding
polymorphism
code is composed of data structures
**** Differences
more direct control over your environment than in Lisp
Because it's stack based, you can return multiple values without going
through contortions.

*** SmallTalk
**** Similarities
object oriented
class based
inheritance
**** Differences

*** English (or whatever)
**** Similarities
Literal objects -- nouns
Executable objects -- verbs
**** Differences
Free form, the order of the words does not matter. What matters is the
order of the objects on the stack. 

*** Data types
**** Integers, strings, boolean, null
**** Names
**** Polymorphic arrays
**** Dictionaries

*** Interpreter
**** PS Functions are executable arrays
**** 3 separate stacks:
***** Operand stack
****** Argument passing
***** Execution stack
****** Array containing PS objects being executed
***** Dictionary stack
****** A PS process's scope

** NeWS extensions to PS
*** Magic dictionaries
**** Process, Canvas, Event, Font
*** Object oriented programming package

* left brain (analytical)
  object deck (True Names)
* right brain (creative)
  cyberspace projector (Vacuum Flowers)

* References:
** True Names
** Vacuum Flowers
** Object Oriented Programming in NeWS
  Owen M. Densmore
  Proc. 3rd Usenix Computer Graphics Workshop, Monterey, CA, November, 1986
** A User-Interface Toolkit in Object-Oriented PostScript
  Owen M. Densmore, David S. H. Rosenthal
** Adobe Red Book
** Adobe Green Book