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List of Names
- Language type:
T - Threaded or stack-based
PostScript is a threaded interpreted
language with stack-based semantics.
While usable for general-purpose
computation, PostScript was specially
designed to drive graphic devices,
initially printers, and has a large set
of operators for rendering onto a page.
In terms of syntax and semantics,
Forth: operators use data from a stack,
and place their results back on the stack.
PostScript data types include floating-point
numbers, strings, fonts, files, vectors,
Defined procedures are simply code
sequences stored in dictionaries.
The essence of PostScript is its model
of execution. In a threaded interpreted
language, a program simply consists of
a series of tokens. The interpreter
processes each token in turn, with
no look-ahead or complex parsing needed.
Supporting this style requires storage
for intermediate results, PostScript
uses several stacks: a code stack, a
data stack, and a dictionary stack. (There
is also a special stack just for graphical
contexts, as needed for the rendering model,
making a total of four stacks.)
Threaded interpreted languages can be
difficult to use, but they offer the
advantage that interpreters for them can
be very compact and fast. As PostScript
was originally designed to execute inside
a printer or similar device with very
little memory, compactness was an important
Several implementations of
PostScript exist, but the two main
ones are the commercial implementations
from Adobe Systems, and the free
Ghostscript implementation from
The current version of PostScript language
is Level 3. PostScript level 2 is also
still very widely used in printers and
other devices. Implementations of
PostScript for GUI systems use a
language dialect called
"Display PostScript," that includes
special operators and slightly different
semantics to accomodate user interaction.
John Warnock et al, Adobe Systems, 1982.
- See Also:
PostScript is a simple language, in
terms of syntax and structure. The
complexity, when learning it, comes
from the richness of its graphics model
and the large set of built-in operators.
Adobe Systems, the company that owns
PostScript, publishes a fine set of books
on learning the language. These first
editions of these books, published around
1985, were originally
blue for the tutorial, red for the reference,
and green for the cookbook. The current
edition of the PostScript reference manual
is no longer red, but it is still sometimes
referred to as "the red book."
The first mass-market printer to support
PostScript was the Apple LaserWriter.
most high-end laser printers and many
typesetters supported the language.
An interesting thing about PostScript is
that most programmers who learn it don't
do so because they want to write PostScript
programs, they do it because they want to
write programs to generate PostScript code
to draw graphics.
PostScript is a descendant of an older
graphics language, also co-invented by
John Warnock, called JaM.
- Sample code:
Descriptions in this dictionary are ©1997-99 Neal Ziring. Some
examples copyright of their respective authors. Some
technologies and languages are trademarked. Permission to
copy descriptions is granted as long as authorship credit is preserved.
Comments on this dictionary, corrections and suggestions, are all welcome.
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Dictionary and script maintained by Neal Ziring, last major modifications 3/18/98. Most recent
additions to dictionary and master list, 1/00.