Text processing

1
Text processing

• Programming Language Design and Implementation
  (4th Edition)
• by T. Pratt and M. Zelkowitz
• Prentice Hall, 2001
• Section 12.1

2
Desktop publishing

• Traditional publication systems
• WYSIWYG - What you see is what you get
• Typewriters examples of early WYSIWYG systems
• More complex today - Multiple fonts, colors,
  embedded graphics
• Need for embedded commands to describe layout of
  document
• Three approaches to desktop publishing
• WYSIWYG
• Page description languages
• Document compiling

3
WYSIWYG

• A common approach in PC world
• Tools like Microsoft Word and Corel WordPerfect
• Embedded commands in document to control layout
  (fonts, colors, font size, location of objects)
• Rich Text Format (RTF) - An ASCII language for
  describing such layout. Can be used to pass
  information among different processors

4
LaTeX

• TeX Document processing system
• developed by Donald Knuth
• a macro processing system for creation of string
  text (i.e., documents)
• Arcane syntax
• LaTeX Macros for TeX
• a set of macros developed for TeX by Leslie
  Lamport
• creates a series of environments and control
  structures similar to programming language
  structures
• for lack of a better term, we often refer to the
  compiling of the book as various chapters are
  processed by the TeX program
• This book developed using LaTeX

5
LaTeX execution

• Executes much like a traditional compiler
• First pass
• Read in text and create output format.
• Create symbol table for all internal references
  (section numbers, page numbers, figure numbers)
• Create table of contents and index, if desired
• Second pass
• Read in text and create output format.
• This time, internal references are correct
  because of symbol table created during pass 1.
• Third pass
• If no changes made to symbol table by pass 2,
  same as pass 2 otherwise repeat pass 2, again
  until no further changes are made to symbol table
• Why more than 2 passes? - Think of putting a
  table of contents at beginning of a report.

6
LaTeX features

• LaTeX creates environments that make TeX easier
  to use. These behave much like C or Pascal scope
  rules
• For example, one can begin and end a list of
  items
• Numbered
• \beginenumerate
• \item text Prints as number 1
• \item text prints as number 2
• \endenumerate End of list
• Bulleted (itemized)
• Named (description)
• Starting new sections or subsections
  automatically adjusts the appropriate section
  numbers. LaTeX has a syntax similar to the
  block-structured style of a programming
  languages.

7
LaTeX structure
8
LaTeX execution

• By invoking LaTeX, the latex.tex macros are read
  into TeX to create commands for chapters,
  sections, subsections, figures, tables, lists,
  and the numerous other structures needed to write
  simple documents.
• The documentstyle command (in LaTeX) allows the
  user to add other style features.
• The required article parameter causes article.sty
  to be read in to tailor latex.tex with commands
  needed for an article. For example, there are no
  chapters in articles, but for style book (i.e.,
  book.sty), chapters are defined.
• 11pt defines the size of the text font (11-point
  type), and art11.sty is read giving additional
  information on line and character spacing for 11-
  point type. The TeX program along with
  article.sty and art11.sty form the standard way
  to process a LaTeX article.
• Mystyle.sty defines addition maccros a user can
  add to tailor LaTeX for a specific document.

9
Page description languages

• A Postscript program consists of five components
• 1. An interpreter for performing calculations. A
  simple postfix execution stack is the basic
  model.
• 2. A language syntax. This is based on Forth.
• 3. Painting extensions. An extension to Forth
  with painting commands for managing the process
  of painting text and pictures on a sheet of
  paper.
• 4. Defines a virtual machine for drawing
  information (text and graphics on a page). The
  showpage operator causes the described page to be
  displayed
• 5. Conventions. A series of conventions, not part
  of the formal Postscript language, that various
  printers use for consistency in presentation. Use
  of these conventions makes it easier for
  transporting postscript documents from one
  system to another.

10
Postscript execution model

• A Postscript program consists of a sequence of
  commands that represent the postfix of the
  algorithm necessary to paint the document.
• Postscript execution begins with two entries
  initially on the stack, which the program may not
  remove
• Systemdict is the system dictionary, which
  represents the initial binding of Postscript
  objects to their internal representation.
• Userdict is the user dictionary, which represents
  the new definitions included within this
  execution of a Postscript program. This may
  include redefinition of primitive objects already
  defined in systemdict.

11
Sample Postscript command

• Each argument is stacked on Postscript stack
• /box newpath 0 0 moveto 0 1 lineto 3 1 lineto 3
  0 lineto closepath def
• /box Add name box to stack. / says this is a
  definition and not to evaluate arguments, only
  move to stack (like quote in LISP)
• newpath start a new path
• moveto Take top two stack arguments and move
  cursor to that (X,Y) location
• lineto Draw line from current cursor to the
  (X,Y) address, which is the top two stack numbers
• closepath Draw line back to newpath location
• def Everything within ... is defined to be
  command box
• Note that the command box now draws a rectangle
  from (0,0) to (0,1) to (3,1) to (3,0) and back to
  (0,0)

12
Summary

• Note differences between models
• LaTeX and MS Word - define the layout of the
  final document
• Postscript - defines a program which computes the
  final layout. A Postscript printer contains an
  interpreter that executes the Postscript program
  to produce the final printed document

13
Postscript execution stacks

• 1. The operand stack contains the operands as
  they are stacked,executed, and unstacked.
• 2. The dictionary stack contains only dictionary
  objects. This stack defines the scope and context
  of each definition.
• 3. The execution stack contains executable
  objects. For the most part, these are functions
  in intermediate stages of execution.
• 4. The graphics state stack manages the context
  for painting objects on the page
• A Postscript program is a sequence of ASCII
  characters. As each token is read, its definition
  is accessed in the stack (by first looking in
  userdict and then systemdict) and executed by an
  appropriate action.

14
Document conventions

• Conventions built into all Postscript
  interpreters
• The leading comment should be!PS That informs
  the interpreter that the file is a Postscript
  program.
• Each page of a document is usually bracketed by a
  save and a restore command to isolate that page
  from the effects of other pages.
• DocumentFonts a list of fonts used in the
  document
• Title an arbitrary string, the title of the
  document
• Creator the name of the program that created
  the file
• CreationDate the date and time of creation
• Pages the number of pages in the document.
• BoundingBox the four values that represent the
  lower left and upper right corners of the page
  that are actually painted by the program. This
  allows the pages to be inserted into other
  documents.

15
Postscript summary

• Postscript was developed to be a virtual machine
  architecture that can be used to create printable
  documents. Postscript of a document is not meant
  to be read by a programmer. However, the syntax
  is quite simple and easily understood.
• Postscript has been developed further by Adobe
  with the creation of their Portable Document
  Format (PDF). PDF is a form of compressed
  Postscript. PDF readers are freely available over
  the Internet, and most Web browsers can display
  PDF files. PDF has become ubiquitous for the
  transmission and display of formatted documents.
• Giving away PDF display programs was a shrewd
  move for Adobe because they sell the Acrobat
  program needed to create PDF documents.