Program      ::= Statement+

Statement    ::= (AssignmentStatement | ImportDeclaration | ExternDeclaration | FunctionCallStatement | IfStatement | WhileStatement | ReturnStatement) SEMICOLON

AssignmentStatement ::= ("let")? ("*")? Expression EQUALS Expression

ImportDeclaration ::= "import" STRING

ExternDeclaration ::= "extern" IDENTIFIER EQUALS Type

FunctionCallStatement ::= (IDENTIFIER | FunctionDefinition) LPAREN FunctionArguments? RPAREN

IfStatement ::= "if" Expression LBRACE Statement* RBRACE -- TODO: Should function definitions be allowed?

WhileStatement ::= "while" Expression LBRACE Statement* RBRACE

ReturnStatement ::= RETURN Expression

FunctionArguments ::= Expression ("," Expression)*

Expression ::= EqualityExpression | AdditiveExpression

EqualityExpression ::= AdditiveExpression ("==" | "<" | ">") AdditiveExpression

AdditiveExpression ::= MultiplicativeExpression (("+" | "-") MultiplicativeExpression)*

MultiplicativeExpression ::= UnaryExpression (("*" | "/" | "%") UnaryExpression)*

UnaryExpression ::= ("!" | "-" | "*") UnaryExpression | PrimaryExpression

PrimaryExpression ::= NUMBER | BOOLEAN | CHAR | STRING | IDENTIFIER | FunctionCallStatement | FunctionDefinition | LPAREN Expression RPAREN

FunctionDefinition ::= LPAREN FunctionParameters? RPAREN ARROW IDENTIFIER LBRACE Statement* ReturnStatement SEMICOLON RBRACE

FunctionParameters ::= IDENTIFIER ":" Type ("," IDENTIFIER ":" Type)*

Type ::= IDENTIFIER | FunctionType

FunctionType ::= LPAREN (Type ("," Type)*)? RPAREN ARROW Type

ParameterTypes ::= Type ("," Type)*