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Features of PostScript Syntax

  • Postfix (hence the name!)
  • Stack
  • Tacit/Concatative

Comments in PostScript start with % and end at newline.

Basic Syntax

First, we have the literals:

  • Integer: 123
  • Real: 123.456
  • Boolean: true, false
  • String: (This is a string)
  • Name: /Name
  • Array: [1 2 3]
  • Dictionary: << /Key /Value >>

Then, we got the operators

  • Arithmetic: add, sub, mul, div, mod
  • Comparison: eq, ne, gt, lt, ge, le
  • Logical: and, or, not
  • Stack manipulation: dup, exch, pop, clear

Closures

We can 'nest' operations by enclosing them in curly braces. These are 'procedures' but I'd like to call them 'closures'. PostScript is a tacit language. This means the code enclosed in curly braces have their own 'closure' --- similar to a function in Posix Shell. Whatever you pushed to stack before opening the curly closure, that is your 'argument stack'. Whatever you define in a 'curly closure' stays there:

/mynameOuter 10 def
10 push
11 push
{ 
  /mynameInner 10 def
  pop print % prints 11
  pop print % prints 10
}

Control Structures using Procedures (or Closures!)

Conditional Execution
Use if and ifelse for conditional operations:

/x 10 def
x 5 gt { (x is greater than 5) show } if

Loops
For repeating operations, you can use loop, repeat, for, and forall.

Example using for:

0 1 10 {  % From 0 to 10 incrementing by 1
    dup  % Duplicates the current number on the stack
    ( ) print
    =  % Prints the number
} for

Functions and Variables

Defining Variables
Use /name to declare a name and def to define a variable:

/x 10 def  % Defines x and sets it to 10

Creating Functions
Functions are defined as procedures and are bound to names:

/addOne { 1 add } def
3 addOne  % Returns 4

Graphics

PostScript is heavily used for drawing:

Basic Shapes

  • Line: newpath 100 100 moveto 200 200 lineto stroke
  • Rectangle: newpath 100 100 moveto 200 0 rlineto 0 100 rlineto -200 0 rlineto closepath stroke
  • Circle: 100 100 50 0 360 arc stroke

Color and Styles
Set colors and line styles using setrgbcolor, setlinewidth, etc.

1 0 0 setrgbcolor  % Red
2 setlinewidth  % Line width of 2
100 100 50 0 360 arc fill  % Draws a filled red circle