Program      ::= Statement+

Statement    ::= (AssignmentStatement | PrintStatement | FunctionCallStatement) SEMICOLON

AssignmentStatement ::= "let" IDENTIFIER EQUALS Expression

PrintStatement ::= PRINT LPAREN Expression RPAREN -- TODO: this won't be needed once functions support arguments

FunctionCallStatement ::= IDENTIFIER LPAREN RPAREN

Expression   ::= AdditiveExpression | FunctionDefinition

AdditiveExpression ::= PrimaryExpression ("+" AdditiveExpression)

PrimaryExpression ::= NUMBER | IDENTIFIER | FunctionCallStatement

FunctionDefinition ::= ARROW LBRACE Statement* ReturnStatement RBRACE

ReturnStatement ::= RETURN Expression SEMICOLON --TODO: I dont like this