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     Introducing ydb -
	A SYMBOLIC DEBUGGER FOR YACC GRAMMARS AND PARSERS
	A COMPLETE GRAMMAR DEVELOPMENT TOOL

ydb is a powerful new symbolic debugger for yacc grammars and parsers.
It provides an extensive set of tools for producing correct, conflict-free 
grammars at translate time, and for providing complete debugging control 
of an operating parser at run time.

ydb also provides crucial extensions to yacc, and frees the user from
yacc's most serious limitations.

FEATURES
********

ydb consists of two debuggers. One is for translate time, when your grammar
is translated into a C language parser; the other is for run time, when you
are using a program with a ydb parser compiled in. Both come with windowed
interfaces, using X and SunView, and terminal interfaces.

At translate time:

- ydb shows you how a parse would proceed if the parser chose one branch
  or the other of a conflict.

- ydb automatically generates a new precedence system to implement your
  decisions about conflicts, and writes it into your grammar file.

- ydb allows you to explore your grammar; for example, one command shows
  you typical strings derived from a nonterminal.

- ydb provides significant extensions to yacc. For example, you can compile
  more than one parser into a program. We built a C interpreter using two
  ydb parsers - one for the preprocessor feeding another for the main
  language.

At run time:

- ydb allows you to trace rule reductions, input tokens, the stack and
  other items of interest in your running parser.

- ydb allows you to break at particular rule reductions, at all rule
  reductions, at particular input tokens, or at other significant points.

- ydb can display the parse tree, grammar states, rules and other
  parser information.

ydb is thoroughly documented, and comes with an indexed user's manual,
a tutorial, a reference manual, a quick reference and extensive on line help.

APPLICATIONS
************

- for developers and maintainers of parsers, command interpreters and front
  ends, ydb provides greatly enhanced productivity and ease of use, plus
  freedom from yacc's most serious limitations.

- for educators, ydb is an ideal tool for demonstrating parsers. Your
  students can watch the stack grow and shrink, trace the rules as they
  are reduced, and in general get a window into a running parser.

- for researchers, ydb provides all the tools you need to take an
  interactive, exploratory approach to your grammars.

FOR MORE INFORMATION
********************

	Bloomsbury Software Group
	P.O. Box 390018
	Mountain View, CA 94039
	(415) 964-3486
	ydb@bsg.com or ...uunet!bsg!ydb