Table of Contents

• 1. def
  • 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. Variable Assignment
    • 1.6.2. Procedure Definitions
    • 1.6.3. Constant Definitions
  • 1.7. Common Pitfalls
  • 1.8. Error Conditions
  • 1.9. Implementation Notes
  • 1.10. Comparison with Related Operators
  • 1.11. See Also

1. def

Associates a key with a value in the current dictionary.

1.1. Syntax

key value def → –

1.2. Stack Effects

Table 1. Before

Level	Object
1	key (usually a name)
0	value (any object)

Table 2. After

Level	Object
(empty)	Current dictionary modified

1.3. Description

def associates key with value in the current dictionary (the one on top of the dictionary stack).

• If key already exists: replaces its value

• If key doesn’t exist: creates new entry

If the current dictionary is in global VM and value is a composite object in local VM, [invalidaccess] error occurs.

1.4. PostScript Level

Level 1 and later

1.5. Examples

Basic definition

/x 42 def       % Define x as 42
/pi 3.14159 def % Define pi

Redefining values

/count 1 def
/count count 1 add def  % count now 2

Defining procedures

/square { dup mul } def
5 square  % Returns 25

Defining in specific dictionary

/mydict 10 dict def
mydict begin
  /localVar 100 def  % Goes into mydict
end

1.6. Common Use Cases

1.6.1. Variable Assignment

/width 612 def
/height 792 def
/margin 72 def

1.6.2. Procedure Definitions

/average { add 2 div } def
/max { 2 copy gt { exch } if pop } def

1.6.3. Constant Definitions

/BLACK 0 def
/WHITE 1 def
/GRAY 0.5 def

1.7. Common Pitfalls

Defines in Current Dictionary - def always uses the current dictionary (top of dict stack), not a specific dictionary.

% Wrong way to define in specific dict
/mydict 5 dict def
/x 42 def  % Goes into userdict, not mydict!

% Right way
mydict begin
  /x 42 def  % Goes into mydict
end

Global/Local VM Mixing - Cannot store local VM objects into global VM dictionaries.

true setglobal  % Global VM mode
/globalDict 10 dict def
globalDict begin
  false setglobal
  /localArray [1 2 3] def  % Error: local in global!
  true setglobal
end

Dictionary Full (Level 1) - In Level 1, dictionary must have capacity. In Level 2, auto-expands.

Use Literal Names - Always use literal names (starting with /) for keys.

1.8. Error Conditions

Error	Condition
[dictfull]	Dictionary full (Level 1 only)
[invalidaccess]	Global VM dict receives local VM value
[limitcheck]	Dictionary expansion exceeds limits (Level 2)
[stackunderflow]	Fewer than 2 operands on stack
[typecheck]	Invalid operand types
[VMerror]	Insufficient VM for new entry or expansion

1.9. Implementation Notes

• Most efficient way to create dictionary entries

• In Level 2, may trigger dictionary expansion

• Key typically a name, but can be any object

• Definition is immediate (no delayed binding)

1.10. Comparison with Related Operators

Operator	Behavior
def	Define in current dictionary
store	Define in first dictionary containing key, or current if not found
put	Put into specific dictionary (requires dict on stack)

1.11. See Also

• load - Look up value from dictionary stack

• store - Store with different semantics

• put - Put into specific dictionary

• begin - Make dictionary current

• where - Find which dictionary contains key