Table of Contents

• 1. stopped
  • 1.1. Syntax
  • 1.2. Stack Effects
  • 1.3. Description
  • 1.4. PostScript Level
  • 1.5. Examples
  • 1.6. Common Use Cases
    • 1.6.1. Error Handler Pattern
    • 1.6.2. Try Multiple Methods
    • 1.6.3. Resource Cleanup
  • 1.7. Common Pitfalls
  • 1.8. Error Conditions
  • 1.9. Implementation Notes
  • 1.10. Standard Error Handler
  • 1.11. Advanced Pattern
  • 1.12. See Also

1. stopped

Executes an object with error catching capability.

1.1. Syntax

any stopped → bool

1.2. Stack Effects

Table 1. Before

Level	Object
0	any (object to execute - typically procedure)

Table 2. After (normal completion)

Level	Object
(varies)	Results from execution
0	false

Table 3. After (stopped)

Level	Object
(varies)	Partial results from execution
0	true

1.3. Description

stopped executes any (typically a procedure).

• If any runs to completion normally: returns false

• If any terminates via stop: returns true

Regardless of outcome, execution resumes at the next object after stopped.

This provides PostScript’s primary error-catching mechanism.

1.4. PostScript Level

Level 1 and later

1.5. Examples

Basic error catching

{
  % Code that might fail
  10 0 div
} stopped {
  % Error occurred
  (Division error caught) print
} if

Normal completion

{
  1 2 add
} stopped
% Returns: 3 false (normal completion)

Explicit stop

{
  errorCondition { stop } if
  normalCode
} stopped {
  (Stopped explicitly) print
} if

1.6. Common Use Cases

1.6.1. Error Handler Pattern

{
  % Main code
  riskyOperation
} stopped {
  % Error handler
  handleerror
} if

1.6.2. Try Multiple Methods

{
  % Try preferred method
  preferredMethod
} stopped {
  % Try fallback
  { fallbackMethod } stopped {
    % Last resort
    defaultMethod
  } if
} if

1.6.3. Resource Cleanup

file (r) file
{
  % Process file
  { processFile } stopped {
    file closefile  % Cleanup
    stop  % Re-raise error
  } if
} stopped {
  % Outer error handler
} if
file closefile  % Always close

1.7. Common Pitfalls

Catches All Errors - stopped catches ALL errors, including those you might not expect.

{
  typoError  % Undefined name
  realCode
} stopped pop
% Error silently caught!

Stack State - Operand and dict stacks not automatically cleaned on stop.

{
  1 2 3
  stop
} stopped {
  % Stack still contains: 1 2 3
  clear  % Must clean up manually
} if

Standard Error Pattern - Default PostScript error handlers use this pattern.

1.8. Error Conditions

Error	Condition
[stackunderflow]	No operand on stack

1.9. Implementation Notes

• Creates new execution context

• Execution stack level saved

• Operand/dictionary stacks not affected by unwinding

• PostScript’s exception handling mechanism

1.10. Standard Error Handler

The default error handler uses stopped:

% Simplified version
{
  % User code
} stopped {
  handleerror
} if

1.11. Advanced Pattern

Nested error handling

{
  % Outer try
  {
    % Inner try
    criticalOperation
  } stopped {
    % Handle inner error
    recoverFromCritical
    stop  % Propagate to outer
  } if

  normalContinuation
} stopped {
  % Handle outer error
  finalRecovery
} if

1.12. See Also

• stop - Terminate stopped context

• exit - Exit loop

• exec - Execute object

• Error Handling (to be documented)