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Lexical Structure

Ovum's source code uses a lexical syntax familiar to C-style and Kotlin-style languages:

Identifiers

Names for variables, functions, classes, etc., consist of letters, digits, and underscores, and must not begin with a digit. For example: myVar, compute_sum, GraphNode. Identifiers are case-sensitive.

Naming Convention: Classes, functions, methods use PascalCase (e.g., Main, ToString, IsLess). Keywords/modifiers remain lowercase (class, interface, var, override, pure, unsafe, etc.).

Keywords

Ovum reserves certain words like fun, class, interface, var, override, pure, if, else, for, while, return, unsafe, val, global, public, private, implements, as, is, null, true, false, typealias, destructor, call, etc. These cannot be used as identifiers.

Literals

  • Numeric literals: integers (e.g., 42, -17) and floating-point numbers (e.g., 3.14, -2.5)
  • Boolean literals: true, false
  • Character literals: single characters in single quotes (e.g., 'A', '\n', '\t')
  • String literals: text in double quotes (e.g., "hello", "world") with escape sequences like "\n" for newline, "\t" for tab, "\\" for backslash, "\"" for quote

Operators and Punctuation

  • Arithmetic: +, -, *, /, %
  • Comparison: ==, !=, <, <=, >, >=
  • Boolean logic: && (logical AND), || (logical OR), ! (negation), ^ (exclusive OR)
  • Assignment: = (reference assignment), := (copy assignment)
  • Null handling: ?. (safe call), ?: (Elvis)
  • Type operations: as (cast), is (type test)
  • Punctuation: , (comma), ; (semicolon), : (colon), () (parentheses), {} (braces), [] (brackets)
  • Namespace resolution: ::

Comments

  • Line comments: start with // and continue to the end of the line
  • Block comments: start with /* and end with */, can span multiple lines. Nested comments are not allowed

Whitespace

Spaces, tabs, and newlines are generally ignored outside of separating tokens. Indentation is not significant (Ovum is not whitespace-sensitive except that newlines can terminate statements if no semicolon is present).

Formal Grammar (EBNF)

Core EBNF; whitespace/comments omitted. Operator precedence in §7.

Program         ::= { Import | Conditional | GlobalDef } ;

Import          ::= "#import" StringLiteral ;
Define          ::= "#define" Identifier [ NumberLiteral ] ;
Undef           ::= "#undef" Identifier ;
Conditional     ::= "#ifdef" Identifier { GlobalDef | Import | Conditional }
                    [ "#else" { GlobalDef | Import | Conditional } ] "#endif"
                 | "#ifndef" Identifier { GlobalDef | Import | Conditional }
                    [ "#else" { GlobalDef | Import | Conditional } ] "#endif" ;

GlobalDef       ::= FunctionDecl | ClassDecl | InterfaceDecl | GlobalVarDecl | TypeAliasDecl ;

FunctionDecl    ::= [ "pure" ] "fun" Identifier "(" [ ParamList ] ")" [ ":" Type ] Block ;
ParamList       ::= Parameter { "," Parameter } ;
Parameter       ::= [ "var" ] Identifier ":" Type ;

ClassDecl       ::= "class" Identifier [ "implements" TypeList ] ClassBody ;
TypeList        ::= Type { "," Type } ;
ClassBody       ::= "{" { ClassMember } "}" ;
ClassMember     ::= FieldDecl | StaticFieldDecl | MethodDecl | DestructorDecl | CallDecl ;

FieldDecl       ::= ( "private" | "public" ) ( "val" | "var" ) Identifier ":" Type [ "=" Expression ] ";" ;
StaticFieldDecl ::= "global" ( "private" | "public" ) ( "val" | "var" ) Identifier ":" Type [ "=" Expression ] ";" ;

MethodDecl      ::= ( "private" | "public" ) [ "override" ] [ "pure" ]
                    "fun" Identifier "(" [ ParamList ] ")" [ ":" Type ] ( Block | ";" ) ;

CallDecl        ::= ( "private" | "public" ) "call" "(" [ ParamList ] ")" [ ":" Type ] ( Block | ";" ) ;

DestructorDecl  ::= ( "private" | "public" ) "destructor" "(" ")" ":" "Void" Block ;

InterfaceDecl   ::= "interface" Identifier InterfaceBody ;  // implicitly extends Object
InterfaceBody   ::= "{" { InterfaceMember } "}" ;
InterfaceMember ::= InterfaceMethod | InterfaceCall ;
InterfaceMethod ::= "fun" Identifier "(" [ ParamList ] ")" [ ":" Type ] ";" ;  // public & virtual
InterfaceCall   ::= "call" "(" [ ParamList ] ")" [ ":" Type ] ";" ;  // public & virtual

GlobalVarDecl   ::= [ "var" ] Identifier ":" Type "=" Expression ";" ;

TypeAliasDecl   ::= "typealias" Identifier "=" Type ";" ;

Type            ::= NullableType | NonNullType ;
NullableType    ::= NonNullType "?" ;
NonNullType     ::= FundamentalType
                 | PrimitiveRefType
                 | "String"
                 | "IntArray" | "FloatArray" | "BoolArray" | "CharArray" | "ByteArray" | "PointerArray"
                 | "ObjectArray"
                 | "StringArray"
                 | Identifier ;              // class/interface names (non-primitive)

FundamentalType ::= "int" | "float" | "bool" | "char" | "byte" | "pointer" ;
PrimitiveRefType ::= "Int" | "Float" | "Bool" | "Char" | "Byte" | "Pointer" ;

Block           ::= "{" { Statement } "}" ;
Statement       ::= VarDeclStmt | ExprStmt | ReturnStmt | IfStmt | WhileStmt | ForStmt | UnsafeStmt | Block ;

VarDeclStmt     ::= [ "var" ] Identifier ":" Type "=" Expression ";" ;
ExprStmt        ::= Expression ";" ;
ReturnStmt      ::= "return" [ Expression ] ";" ;
IfStmt          ::= "if" "(" Expression ")" Statement [ "else" Statement ] ;
WhileStmt       ::= "while" "(" Expression ")" Statement ;
ForStmt         ::= "for" "(" Identifier "in" Expression ")" Statement ;
UnsafeStmt      ::= "unsafe" Block ;

Expression      ::= Assignment ;
Assignment      ::= ElvisExpr [ ("=" | ":=") Assignment ] ;

ElvisExpr       ::= OrExpr [ "?:" ElvisExpr ] ;  // right-assoc

OrExpr          ::= AndExpr { "||" AndExpr } ;
AndExpr         ::= XorExpr { "&&" XorExpr } ;
XorExpr         ::= EqualityExpr { "^" EqualityExpr } ;

EqualityExpr    ::= RelExpr { ("==" | "!=") RelExpr } ;
RelExpr         ::= AddExpr { ("<" | "<=" | ">" | ">=") AddExpr } ;
AddExpr         ::= MulExpr { ("+" | "-") MulExpr } ;
MulExpr         ::= UnaryExpr { ("*" | "/" | "%") UnaryExpr } ;

UnaryExpr       ::= ("!" | "-" | "&" | "*") UnaryExpr
                 | Postfix ;

Postfix         ::= Primary { PostfixOp } ;
PostfixOp       ::= "." Identifier
                 | "." Identifier "(" [ ArgList ] ")"
                 | "(" [ ArgList ] ")"          // function call or callable object call
                 | "as" Type                    // explicit cast; downcast yields nullable type
                 | "is" Type                    // type test → bool
                 | "?." Identifier [ "(" [ ArgList ] ")" ]  // safe call chain
                 | "?." "(" [ ArgList ] ")"     // safe callable object call
                 ;

Primary         ::= Identifier
                 | Literal
                 | "(" Expression ")"
                 | NamespaceRef
                 | FunctionLiteral ;

FunctionLiteral ::= "fun" "(" [ ParamList ] ")" [ ":" Type ] Block ;

NamespaceRef    ::= Identifier "::" Identifier ;
ArgList         ::= Expression { "," Expression } ;

Literal         ::= NumberLiteral | StringLiteral | CharLiteral | "true" | "false" ;