Table of Contents

• 1. xcheck
  • 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. Validating Procedure Arguments
    • 1.6.2. Type-Safe Operations
    • 1.6.3. Debugging
  • 1.7. Common Pitfalls
  • 1.8. Error Conditions
  • 1.9. Implementation Notes
  • 1.10. Executable vs. Literal Summary
  • 1.11. See Also

1. xcheck

Tests whether an object has the executable attribute.

1.1. Syntax

any xcheck → bool

1.2. Stack Effects

Table 1. Before

Level	Object
0	any (any object)

Table 2. After

Level	Object
0	bool (true if executable, false if literal)

1.3. Description

xcheck tests whether the operand has the executable or literal attribute:

• Returns true if the object is executable

• Returns false if the object is literal

This tests the executable/literal attribute only, not the access attribute (e.g., execute-only, readonly).

1.4. PostScript Level

Level 1 and later

1.5. Examples

Checking names

/abc xcheck      % false (literal name)
abc xcheck       % true (executable name) - if abc is defined

Checking procedures

{ 1 2 add } xcheck      % true (procedures are executable)
{ 1 2 add } cvlit xcheck  % false (converted to literal)

Checking numbers and strings

123 xcheck       % false (numbers always literal)
(text) xcheck    % false (strings always literal)

1.6. Common Use Cases

1.6.1. Validating Procedure Arguments

/execute-if-proc {
  dup xcheck {
    exec
  } {
    % Not executable, handle differently
  } ifelse
} def

1.6.2. Type-Safe Operations

/safe-exec {
  dup xcheck not {
    /typecheck cvx exec
  } if
  exec
} def

1.6.3. Debugging

/show-attr {
  dup xcheck
  { (executable) }
  { (literal) }
  ifelse print
} def

1.7. Common Pitfalls

Tests Attribute, Not Access - xcheck does not test access permissions like execute-only.

% xcheck returns true even for execute-only objects
proc executeonly xcheck  % true

Most Objects Are Literal - Numbers, strings, and array literals are all literal by default.

Combine with type - Use type to check object type along with executability.

1.8. Error Conditions

Error	Condition
[stackunderflow]	No operand on stack

1.9. Implementation Notes

• Very fast operation (checks single bit in object header)

• Does not modify the object

• Works on any object type

• Complementary test to attribute queries

1.10. Executable vs. Literal Summary

Object Type	Default Attribute	Can Change?
Integer	Literal	No
Real	Literal	No
Boolean	Literal	No
String	Literal	Yes
Name	Depends on / prefix	Yes
Array	Literal ([ ])	Yes
Procedure	Executable ({ })	Yes
Mark	Literal	No
Null	Literal	No
Operator	Executable	No

1.11. See Also

• cvlit - Convert to literal attribute

• cvx - Convert to executable attribute

• rcheck - Test if readable

• wcheck - Test if writable

• type - Get object type