Doomsday Manual

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<- script:reference|Reference guide ^ ^ Operator expressions ->

====== Basic expressions ======

===== Numbers and strings =====

All numbers are internally stored as 64-bit floats.

  $ print 5, 5.5, -3.141592657
  5 5.5 -3.14159

Hexadecimal numbers use the "0x" prefix.

  $ print 0x100, 0X123
  256 291

Underscores can be inserted in numbers at any points. This is only to improve readability for humans; the parser ignores them.

  $ print 'Underscores for readability: %x' % 0x0012_3456
  Underscores for readability: 0x123456
  
Text strings can use single, double, or triple quotes. Single and double are semantically equal. C-like escape sequences are supported, for example ''\n'' for a newline. Triple-quoted strings can contain newlines and quotes without having to escape them with a backslash.

  $ print "Hello", 'World'
  Hello World
  
  $ print """I can "span"
  newlines."""
  I can "span"
  newlines.


===== Arrays and dictionaries =====

Arrays are created using brackets around comma-separated elements.

  $ print [1, 2, 3]
  [ 1, 2, 3 ]

The elements of arrays can be of any type.

  $ print [1, [2, 3], 4]
  [ 1, [ 2, 3 ], 4 ]

Dictionaries contain key-value pairs. A dictionary is created with curly brackets. 

  $ print {'a': 10, 'b': 5}
  { a: 10, b: 5 }

Keys and values can be of any type. 
  
  $ print {'a': 'b', 1: ['b', {5:6, 6:7}], ['array', 'as', 'key']: 'oh my'}
  { 1: [ b, { 5: 6, 6: 7 } ], [ array, as, key ]: oh my, a: b }


===== Other value types =====

Time values store a specific point in time. The built-in function ''Time()'' returns the current local time.

  $ print 'The time is now:', Time()
  The time is now: 2019-11-19 21:33:16.501


===== Constants =====

There are reserved keywords for commonly used constants.

  $ print True, False, None, Pi
  True False (none) 3.14159


===== Built-in functions =====

The built-in ''len()'' function returns the size/length of its argument.

  len("abcd") ⇒ 4
  len([1, 2, 3, 4]) ⇒ 4
  len({1:2, 3:5, 8:13}) ⇒ 3

There are functions for extracting all the keys or all the values of a dictionary into an array.

  dictkeys({1:2, 3:5, 8:13}) ⇒ [ 1, 3, 8 ]
  dictvalues({1:2, 3:5, 8:13}) ⇒ [ 2, 5, 13 ]

The functions ''Text()'' and ''Number()'' convert the argument to a text string or a number.

  $ print Text(123), Number("123")
  123 123

One can give a string argument to the ''Time()'' function to parse as a time and date.

  $ print "Beginning of March 2011:", Time("2011-03-01")
  Beginning of March 2011: 2011-03-01 00:00:00.000
  
  $ print Time("2000-01-02 03:04:05.678")
  2000-01-02 03:04:05.678

If the parsing fails, the resulting value represents an undefined point in time. A valid time evaluates to True and an undefined time evaluates to False when used as a boolean condition.
  
  $ print 'Invalid time:', Time("123-123"), Time("")
  Invalid time: (undefined Time) (undefined Time)

The ''timedelta()'' function calculates the difference between two points in time.
  
  $ print 'Thousand seconds later:', timedelta(Time(), Time() + 1000)
  Thousand seconds later: 1000

The ''serialize()'' and ''deserialize()'' functions convert their argument to/from a sequence of bytes. This is useful for instance when saving and reading values to/from a file. All values created in scripts can be serialized. The contents of a serialized block of memory cannot be modified via Doomsday Script.

  $ a = [1, 'One', {1:'One'}]
  
  $ print a
  [ 1, One, { 1: One } ]
  
  $ b = serialize(a)
  
  $ print b
  (Block of 46 bytes)
  
  $ print deserialize(b)
  [ 1, One, { 1: One } ]

The ''eval()'' function evaluates its argument as a script and returns the return value from it. The script gets runs in the same namespace where ''eval()'' was called.

  $ a = eval(""" 'arg' + 'ument' """)
  
  $ print a
  argument
  
  $ eval("""print "Printed from eval():", a""")
  Printed from eval(): argument
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