Lingo bytecode

File Format
Name	Lingo bytecode
Ontology	Electronic File Formats Development Lingo bytecode

This is a partial, work-in-progress examination of the bytecode created when Lingo code is compiled in Macromedia Director 4.0. This is also sometimes known as IML, or Idealized Machine Language. It describes instructions for a stack-based virtual machine.

Each instruction is one, two or three bytes.

• If the first byte is in the range 0x00-0x3F, then the full instruction is one byte.
• If the first byte is in the range 0x40-0x7F, then the full instruction is two bytes.
• If the first byte is in the range 0x80-0xFF, then the full instruction is three bytes.

Constant blobs like string literals are stored after the bytecode, and referred to by records that are six bytes long regardless of the actual length of the data. This means the first constant will be referred to as 0x00, the second constant as 0x06, the third as 0x0C, and so on. Integer literals over 32767 and floating-point number literals are also stored as constants.

There is also a namelist for referring to external identifiers, stored separately from the bytecode. This is a simple array of strings.

01	exit			Leave the current function immediately and return to its caller. Automatically added as the final step of a function.
02
03	0 FALSE		+1	Push zero onto the stack.
04	(a * b)	-2	+1	Pop two values from the stack, multiply them together and push the result.
05	(a + b)	-2	+1	Pop two values from the stack, add them together and push the result.
06	(a - b)	-2	+1	Pop two values from the stack, subtract the second from the first and push the result.
07	(a / b)	-2	+1	Pop two values from the stack, divide the first by the second and push the result.
08
09	(-a)	-1	+1	Pop one value from the stack, negate it and push the result.
0A	(a & b)	-2	+1	Pop two values from the stack, concatenate them and push the resulting string.
0B	(a && b)	-2	+1	Pop two values from the stack, concatenate them with one space character added in between, and push the resulting string.
0C	(a < b)	-2	+1	Pop two values from the stack, push 1 if the first is less than the second and 0 if not.
0D	(a <= b)	-2	+1	Pop two values from the stack, push 1 if the first is less than or equal to the second and 0 if not.
0E	(a <> b)	-2	+1	Pop two values from the stack, push 0 if the two values are the same and 1 if they are not.
0F	(a = b)	-2	+1	Pop two values from the stack, push 1 if the two values are the same and 0 if they are not.
10	(a > b)	-2	+1	Pop two values from the stack, push 1 if the first is greater than the second and 0 if not.
11	(a >= b)	-2	+1	Pop two values from the stack, push 1 if the first is greater than or equal to the sceond and 0 if not.
12	(a and b)	-2	+1	Pop two values from the stack, push 1 if both are logically true and 0 if not.
13	(a or b)	-2	+1	Pop two values from the stack, push 1 if either are logically true and 0 if not.
14	(!a)	-1	+1	Pop one value from the stack, push 0 if it is logically true and 1 if not.
15	(a contains b)	-2	+1	Pop two values from the stack, push 1 if the first is a string that contains the second and 0 if not.
16
17	(char a of c) (char a to b of c)	-9	+1	String slice. The nine arguments it takes from the stack are: -9 Index of the first character -8 Index of the last character (or zero if unspecified) -7 Unknown -6 Unknown -5 Unknown -4 Unknown -3 Unknown -2 Unknown -1 The string itself Use zero for the unknown parameters. Lingo uses one-based indexing for string slicing.
18
19
1A
1B	(field 1)	-1	+1	Pop a cast ID (name or number), push the value of that cast member's text property.
1C
1D
1E		-1	+1	Some kind of list transformation or check, seen used just before setting the actorList to []. More research is needed to know exactly what is happening there.
1F	[#key: value]	-1	+1	Pops a list that must be in the form [#symbol1, val1, #symbol2, val2 ...] to transform into [#symbol1: val1, #symbol2: val2 ...]

41 XX	1 .. 127		+1	Push integer of value XX, which must be between 1 and 127, inclusive. To push zero, use 03. To push larger integers, use 81 XX YY.
42 XX	a, b, c	-XX	+1	Pop the specified number of values off the top of the stack, create an unparenthesized argument list containing them (i.e. for a call statement like myFunction 1, 2, 3), and push that to the stack.
43 XX	[a, b, c]	-XX	+1	Pop the specified number of values off the top of the stack, create a list for them (which can also be used for a parenthesized call expression like set result = myFunction(1, 2, 3)), and push that to the stack.
44 XX	"literal" 0.5 32768		+1	Push a constant from local constant records onto the stack. These records seem to be six bytes long (regardless of the actual size of the constant value), so pushing the first one is 44 00, the second is 44 06, the third is 44 0C, etc.
45 XX	#symbol		+1	Push a symbol with a name from namelist[XX]. Note that the name will be stored as "name", not "#name".
46 XX
47 XX
48 XX
49 XX	(someGlobal) where previously declared: global someGlobal		+1	Push the value of a global variable with a name from namelist[XX].
4C XX	(someLocal)		+1	Push the value of a local variable. The local variable records seem to be 6 bytes long, so the first is pushed with 4C 00, the second with 4C 06, etc.
4D XX
4E XX
4F XX	set someGlobal = 0	-1		Pop one value and use it to set the global variable with name from namelist[XX].
50 XX
51 XX
52 XX	set someLocal = 0	-1		Pop one value and use it to set a local variable. See code 4C 00 for a note about local variable records.
53 XX
54 XX	end repeat			Unconditional backwards jump by XX bytes, relative to the first byte of this instruction.
55 XX
56 XX
57 XX	someFunction 1,2,3 (someFunction(1,2,3))	-1	+1 OR +0	Call the function with name from namelist[XX]. The top value on the stack must be an argument list. If the argument list was created with code 43 XX, one return value will be pushed to the stack. If the argument list was created with code 42 XX, no return value will be pushed.
58 XX
59 16	put "extra" into textVar	-1		(Not sure how the target value is specified, needs more research)
59 25	put "extra" after textVar	-1		(See above)
59 35	put "extra" before textVar	-1		(See above)
5A XX
5B 05	delete word 3 of textVar	-1		(See above)
5C 00	(the date)	-1	+1	Pop a date formatting ID, and push the current date, formatted according to it: 09 the date, the short date 0A the abbreviated date, the abbrev date, the abbr date 0B the long date
5C 03	(the checkMark of menuItem 1 of menu 1)	-3	+1	Pop [item ID, menu ID, property ID] and push the value of the specified menu item property, using these property IDs: 02 checkMark 03 enabled
5C 06	(the cursor of sprite 3)	-2	+1	Pop [sprite ID, property ID] and push the value of the specified sprite property, using these property IDs: 04 castNum 05 constraint 06 cursor
5C 08	(the number of castMembers)	-1	+1	Pop a stat ID from the stack and push the value of the stat, using these stat IDs: 02 (the number of castMembers)
5C 09	(the picture of cast "bob") (the name of cast 3)	-2	+1	Pop [cast ID, property ID] from the stack and push the value of the cast property, using these property IDs: 01 name 02 text 08 picture 0A number 11 foreColor 12 backColor
5D 03	set the enabled of menuItem 3 of menu 5 = FALSE	-3		Pop [menuItem ID, menu ID, new value, property ID] and set the menu item property. See the table for code 5C 03 for menu item property IDs.
5D 06	set the constraint of sprite 3 = 0	-3		Pop [sprite ID, new value, property ID] and set the sprite property. See the table for code 5C 06 for sprite property IDs.
5D 09	set the backColor of cast "bob" = 0	-3		Pop [cast ID, new value, property ID] and set the cast property. See the table for code 5C 09 for cast property IDs.
5E XX
5F XX	(the someProperty)		+1	Push the value of the contextual property with the name at namelist[XX].
60 XX	set the someProperty = 0	-1		Pop a value and use it to set the contextual property with the name at namelist[XX].
61 XX	(the someProperty of someVariable)	-1	+1	Pop a property-owning object from the stack, and push the value of this object's property with the name at namelist[XX].

81 XX YY	128 .. 32767		+1	Push the integer ((XX * 0x100) + YY). Larger integers and floats are pushed using constants.
93 XX YY	exit repeat			Unconditional jump: Advance by ((XX * 0x100) + YY) bytes, relative to the first byte of this instruction (i.e. it may be 3 more than you are expecting)
95 XX YY	if somethingIsTrue then repeat while somethingIsTrue	-1		Conditional jump: Pop a value, and if it is logically FALSE, advance by ((XX * 0x100) + YY) bytes, relative to the first byte of this instruction

Syntactic Sugar

Some functions get special syntax when written out in source code, but the compiler just transforms it into something more common. Here is a mapping that shows the equivalent in plain, generalized Lingo that gets used for the bytecode.

Specialized Syntax	Generalized Syntax
play frame 10 of movie "theMovie"	play 10, "theMovie"
play frame 10	play 10
play movie "theMovie"	play 1, "theMovie"
play done	play
repeat with i = 15 to 20 ... end repeat	set i = 15 repeat while i <= 20 ... set i = i + 1 end repeat
repeat with i = 15 down to 10 ... end repeat	set i = 15 repeat while i >= 10 ... set i = i - 1 end repeat
sound fadeIn 5	sound #fadeIn, 5
sound fadeIn 5, 10	sound #fadeIn, 5, 10
sound fadeOut 5	sound #fadeOut, 5
sound fadeOut 5, 10	sound #fadeOut, 5, 10