Uxntal Labels

A label is a non-numeric, non-opcode, and non-runic symbol that correspond to a number between 0 and 65536. A label name is made of two parts, a scope and a sublabel. Sublabels can be added to a scope with the &name rune, or by writing the full name, like @scope/name. Note that a labels like bed, add and cafe are considered numeric.

Functions are simply labels that will be jumped to, and returned from.

@func ( a b -- c )
	&loop
		INC GTHk ?&loop
	ADD JMP2r

Constants are labels that hold a specific value through the entire execution of the program. They allow to assign a name to a number, making the code more readable.

|1400 @limit

Enums are labels with padded members of equal sizes that can be used as constants in a program, they typically begin by rolling back the program address with |00:

|00 @Suit &clubs $1 &diamonds $1 &hearts $1 &spades

Structs are labels with padded members of different sizes, that maps on a data-structure, they typically begin by rolling back the program address with |00:

|00 @Person &name $2 &age $1 &height $2

Labels can also be used with the padding runes to define a global length. For example, if one needs to specify a length of 0x30 for multiple members of a struct, a value can be specified as follow:

|30 @length
|00 @Struct &field $length

Scope

Uxntal objects are defined statically and allow for the enclosed methods to access encapsulated local &members. The example below contains an object with the method set-color, accessible from outside the scope as pen/set-color.

@pen
	&position &x $2 &y $2
	&color $1

&set-color ( color -- )
	,/color STR
	JMP2r

New methods and members can extend an existing scope from anywhere by creating a label with the scope name followed by a slash and the name of the extension. The &labels declared within the extension have the same access to local labels as the rest of the object.

@pen/get-position ( -- x* y* )
	,/x LDR2 ,/y LDR2
	JMP2r

When calling local methods the scope's name can be omitted, starting at the slash, like /method:

@pen/paint ( -- )
	/get-position canvas/draw-line-to
	JMP2r

Addressing

A labels is a way of assigning a name to a number. There are six ways to get the number corresponding to that label. Literal addressing prefixes the label with a LIT for Relative and Zero-Page addressing, and LIT2 for absolute addressing.

• Literal Relative, like ,label, pushes a relative distance byte to the label.
• Literal Zero-Page, like .label, pushes an absolute address byte to the label.
• Literal Absolute, like ;label, pushes an absolute address short to the label.
• Raw Relative, like _label, writes a relative distance byte to the label.
• Raw Zero-Page, like -label, writes an absolute address byte to the label.
• Raw Absolute, like =label, writes an absolute address short to the label.

Raw addressing is used for building data-structures and more advanced programs. A relatively common usage of raw runes is to create literals directly into the return stack:

[ LITr ab ] STHr INC ac

Anonymous Labels

Anonymous labels are designated with a curly bracket that points to its associated closing bracket, and can be nested. Under the hood, the opening bracket assembles to the address of the closing bracket which allows the destination address to be used like any other label such as a JCI ?{, a JMI, !{ or a plain literal ;{. Here are some example data-structures:

@counted-string
	_{ "foo 20 "bar }

@linked-list
	={ ={ "A } ={ "B ={ "C } } }

Unless Blocks

It is important to notice that in the case of a conditional jump, the lambda's content is jumped over when the flag byte is true.

[ LIT2 &last $1 -Mouse/state ] DEI DUP ,&last STR
DUP2 #0001 NEQ2 ?{ ( on down ) }
DUP2 #0101 NEQ2 ?{ ( on drag ) }
DUP2 #0100 NEQ2 ?{ ( on release ) }
POP2

The opening curly bracket assembles to a unique label reference, and the closing bracket to a corresponding matching label definition. They do not affect the scope.

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