keyword := 'if' | 'while' | 'until' | 'repeat' | 'for' | 'do' | 'break' |
           'print' | 'else' | 'end'
identifier := /[a-zA-Z][[:alnum:]]+/
number := /\d+/
boolean-literal := 'true' | 'false'

factor := '(' boolean-expression ')' | identifier | number
signed-factor := '-' factor | '+' factor | factor
term := signed-factor (/[*/]/ signed-factor)*
arithmetic-expression := term (/[-+]/ term)*

bit-op := '|' | '&' | '^'
bit-expression := arithmetic-expression (bit-op arithmetic-expression)*

rel-op := '==' | '!=' | '>' | '>=' | '<' | '<='
relation := bit-expression (rel-op bit-expression)*

boolean-factor := boolean-literal | relation
not-factor := '!' boolean-factor | boolean-factor
boolean-term := not-factor ('&&' not-factor)*
boolean-expression := boolean-term ('||' boolean-term)*

assignment := identifier '=' boolean-expression

expression := assignment | boolean-expression