characterLiteral
         ::= letter
           | digit
           | [\s]

stringlit
         ::= ["] ( characterLiteral | '\\' [nsrt'"\\] )* ["]

letter   ::= [a-zA-Z]

digit    ::= [\d]

keyword  ::= 'var'
           | 'while'
           | 'and'
           | 'or'
           | 'not'
           | 'true'
           | 'false'
           | 'return'
           | 'for'
           | 'each'
           | 'do'
           | 'if'
           | 'then'
           | 'else'
           | 'in'
           | 'both'
           | 'ava'
           | 'times'
           | type

id       ::= letter ( letter | digit | '_' )*

key      ::= id
           | stringlit

assignop ::= '='
           | '+='
           | '-='
           | '*='
           | '/='

relop    ::= '<'
           | '>'
           | '<='
           | '=='
           | '>='
           | '!='

appendop ::= '@'

consop   ::= '::'

addop    ::= '+'
           | '-'

mulop    ::= '*'
           | '/'
           | '%'

prefixop ::= '-'
           | 'not'

postfixop
         ::= '++'
           | '--'

exponent ::= '^^'

intlit   ::= [\d]+

boolit   ::= 'true'
           | 'false'

comment  ::= '//' [^\r\n]* [\r\n]
           | '***' ( [.] | [\n] )* '***'

type     ::= 'int'
           | 'string'
           | 'float'
           | 'bool'
           | 'function'
           | 'list'
           | 'object'
           | 'set'