GDScript grammar

This is the formal grammar of GDScript written in EBNF, for reference purposes.

Nota

This grammar is descriptive only, derived from the reference documentation and current implementation. The GDScript parser is not generated from a grammar definition. Inconsistencies here likely mean an error in this grammar, not a bug in GDScript.

(* GDScript EBNF grammar.
   Uppercase words are terminals generated by the tokenizer.
   INDENT/DEDENT are not generated by the tokenizer yet, but they are added
   here for reading convenience.
   Naturally, this only cover syntax. Semantics can't be inferred from this
   description.
*)

program = [ inheritance NEWLINE ] [ className ] { topLevelDecl } ;

inheritance = "extends" ( IDENTIFIER | STRING ) { "." IDENTIFIER } ;
className = "class_name" IDENTIFIER [ "," STRING ] NEWLINE ;

topLevelDecl
    = classVarDecl
    | constDecl
    | signalDecl
    | enumDecl
    | methodDecl
    | constructorDecl
    | innerClass
    | "tool"
    ;

classVarDecl = [ "onready" ] [ export ] "var" IDENTIFIER [ ":" typeHint ]
    [ "=" expression ] [ setget ] NEWLINE ;
setget = "setget" [ IDENTIFIER ] [ "," IDENTIFIER] ;
export = "export" [ "(" [ BUILTINTYPE | IDENTIFIER { "," literal } ] ")" ] ;
typeHint = BUILTINTYPE | IDENTIFIER ;

constDecl = "const" IDENTIFIER [ ":" typeHint ] "=" expression NEWLINE ;

signalDecl = "signal" IDENTIFIER [ signalParList ] NEWLINE ;
signalParList = "(" [ IDENTIFIER { "," IDENTIFIER } ] ")" ;

enumDecl = "enum" [ IDENTIFIER ] "{" [ IDENTIFIER [ "=" INTEGER ]
    { "," IDENTIFIER [ "=" INTEGER ] } [ "," ] ] "}" NEWLINE ;

methodDecl = [ rpc ] [ "static" ] "func" IDENTIFIER "(" [ parList ] ")"
    [ "->" typeHint] ":" stmtOrSuite ;
parList = parameter { "," parameter } ;
parameter = [ "var" ] IDENTIFIER [ ":" typeHint ] [ "=" expression ] ;
rpc = "remote" | "master" | "puppet"
    | "remotesync" | "mastersync"  | "puppetsync";

constructorDecl = "func" IDENTIFIER "(" [ parList ] ")"
    [ "." "(" [ argList ] ")" ] ":" stmtOrSuite ;
argList = expression { "," expression } ;

innerClass = "class" IDENTIFIER [ inheritance ] ":" NEWLINE
    INDENT [ inheritance NEWLINE ] topLevelDecl { topLevelDecl } DEDENT ;

stmtOrSuite = stmt | NEWLINE INDENT suite DEDENT ;
suite = stmt { stmt };

stmt
    = varDeclStmt
    | ifStmt
    | forStmt
    | whileStmt
    | matchStmt
    | flowStmt
    | assignmentStmt
    | exprStmt
    | assertStmt
    | yieldStmt
    | preloadStmt
    | "breakpoint" stmtEnd
    | "pass" stmtEnd
    ;
stmtEnd = NEWLINE | ";" ;

ifStmt = "if" expression ":" stmtOrSuite { "elif" expression ":" stmtOrSuite }
    [ "else" ":" stmtOrSuite ] ;
whileStmt = "while" expression ":" stmtOrSuite;
forStmt = "for" IDENTIFIER "in" expression ":" stmtOrSuite ;

matchStmt = "match" expression ":" NEWLINE INDENT matchBlock DEDENT;
matchBlock = patternList ":" stmtOrSuite { patternList ":" stmtOrSuite };
patternList = pattern { "," pattern } ;
(* Note: you can't have a binding in a pattern list, but to not complicate the
grammar more it won't be restricted syntactically *)
pattern = literal | BUILTINTYPE | CONSTANT | "_" | bindingPattern
    | arrayPattern | dictPattern ;
bindingPattern = "var" IDENTIFIER ;
arrayPattern = "[" [ pattern { "," pattern } [ ".." ] ] "]" ;
dictPattern = "{" [ keyValuePattern ] { "," keyValuePattern } [ ".." ] "}" ;
keyValuePattern = STRING [ ":" pattern ] ;

flowStmt
    = "continue" stmtEnd
    | "break" stmtEnd
    | "return" [ expression ] stmtEnd
    ;

assignmentStmt = subscription "=" expression stmtEnd;
varDeclStmt = "var" IDENTIFIER [ "=" expression ] stmtEnd;

assertStmt = "assert" "(" expression [ "," STRING ] ")" stmtEnd ;
yieldStmt = "yield" "(" [ expression "," expression ] ")" ;
preloadStmt = "preload" "(" CONSTANT ")" ;

(* This expression grammar encodes precedence. Items later in the list have
higher precedence than the ones before. *)
exprStmt = expression stmtEnd ;
expression = cast [ "[" expression "]" ] ;
cast = ternaryExpr [ "as" typeHint ];
ternaryExpr = logicOr [ "if" logicOr "else" logicOr ] ;
logicOr = logicAnd { ( "or" | "||" ) logicAnd } ;
logicAnd = logicNot { ( "and" | "&&" ) logicNot };
logicNot = ( "!" | "not" ) logicNot | in;
in = comparison { "in" comparison };
comparison = bitOr { ( "<" | ">" | "<=" | ">=" | "==" | "!=" ) bitOr } ;
bitOr = bitXor { "|" bitXor } ;
bitXor = bitAnd { "^" bitAnd } ;
bitAnd = bitShift { "&" bitShift } ;
bitShift = minus { ( "<<" | ">>" ) minus } ;
minus = plus { "-" plus } ;
plus = factor { "+" factor } ;
factor = sign { ( "*" | "/" | "%" ) sign } ;
sign = ( "-" | "+" ) sign | bitNot ;
bitNot = "~" bitNot | is ;
is = call [ "is" ( IDENTIFIER | BUILTINTYPE ) ] ;
call = attribute [ "(" [ argList ] ")" ];
attribute = subscription { "." IDENTIFIER } ;
subscription = primary [ "[" expression "]" ] ;
primary = "true" | "false" | "null" | "self" | literal | arrayDecl
    | dictDecl | "(" expression ")" ;

literal = STRING | NUMBER | IDENTIFIER | BUILTINTYPE
    | "PI" | "TAU" | "NAN" | "INF" ;
arrayDecl = "[" [ expression { "," expression } "," ] "]" ;
dictDecl = "{" [ keyValue { "," keyValue } "," ] "}" ;
keyValue
    = expression ":" expression
    | IDENTIFIER "=" expression
    ;