Variables

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Declaring variables

As in other languages, you can declare variables in MCFPP to store, pass and process data.

Typical declaration:

#var <identifier> [as <type>] [= expression or value]
var i as int = 5;
var b as int = i * 6;

#type inferred
var j = 5; # j is inferred as int
var k = 5.0; # k is inferred as float
var i; # error: missing initializer, cannot infer

Identifiers may contain letters and digits. In the same scope a name can be declared only once.

Variable types

MCFPP has primitive and composite types. Primitives are built-in; composite types (classes, templates, etc.) are user-defined. Current primitives:

Type	Description	Example
int	integer	1,114514,-5
float	single-precision float	2.5,1.0,9.5e6
bool	boolean	true,false
nbt	NBT data	"a":{"b":"c"},"a":[1,2,3,4]
list	list	[1,2,3,4],["a","b","c"]
dict	dictionary	{"a":1,"b":2,"c":3}
map	richer map with more features	same as above
string	string (NBT string tag)	"mcfpp","qwq"
text	text components	"mcfpp",{"text":"mcfpp","color":"#114514"}
entity	single entity (stores UUID)	—
selector	target selector	@a,@p

Brief descriptions (expandable):

int

int is the basic integer type. It can be positive, negative, or zero, and supports decimal, binary, octal, hex, etc. int values are stored as scoreboard variables, so they have scoreboard size limits.

float

A floating‑point number with single precision. Supports decimal and scientific notation. MCFPP float ops rely on Xiaodou's math library. Float operations are implemented via scoreboard math and have modest overhead.

bool

Boolean with values true or false. Stored as a scoreboard variable.

nbt

NBT data, often acting as an NBT pointer (stores an NBT path). Many composite types (list, map, etc.) are based on NBT operations.

list

List type. Implements most ArrayList methods from Java; stored as an NBT list.

dict

Dictionary stored as an NBT compound. Due to Minecraft limits, dict supports basic key insert/remove but not iteration. Use map for more operations.

map

A richer wrapper over dict with more features (implements most HashMap methods). Provides more functionality at the cost of additional overhead.

string

String type (NBT string tag).

text

Raw JSON text. Unlike string, text can include formatting (color, bold, etc.). Stored as an NBT compound.

entity

Represents a single entity. Stored as a UUID integer NBT array.

selector

Represents a target selector. Stored as a string.

Variable modifiers

Modifiers express variable properties: dynamic, const.

• dynamic

If a variable is a literal (e.g. int i = 5;), the compiler may optimize it (e.g. i += 7 becomes 12 at compile time instead of scoreboard commands). dynamic forces runtime/dynamic behavior even for literals. Example: dynamic int i = 5; will not be optimized away.

• const

const marks a compile-time constant whose value is fixed at compile time and cannot change. It must be initialized on declaration.

Compile-time optimizations

The compiler tracks compile-time-known values and optimizes accordingly. When a variable is assigned a literal, the compiler remembers its value until tracking is lost.

var i = 5;  # compiler records i = 5
i += 7;     # compiler treats i as 12; no scoreboard commands emitted
var j = i;  # compiler also knows j's value

dynamic var x as int;
j = x;      # compiler loses precise value for j
j += 1;     # compiler will emit scoreboard commands