lowercaseLetter = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z".
uppercaseLetter = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z".
letter = lowercaseLetter | uppercaseLetter.
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9".
nl = "\n".

ident = letter { letter | digit }.
integer = digit { digit }.

factor = ident | integer | "(" expression ")" | "~" factor.
term = factor {("*" | "/" | "%" | "&") factor}.
simple_expression = ["+" | "-"] term {("+" | "-" | "|") term}.
expression = simple_expression [ ( "==" | "!=" | ">=" | "<=" | ">" | "<" ) simple_expression ].
ident_list = ident { "," ident }.
expression_list = expression { "," expression }.

program = function program.
function = "fun" ident "[" [ ident_list ] "]" statements "end".

statement = [ if_statement | while_statement | assignment | function_call | return_statement ].
statements = statement { nl statement }.

if_statement = "if" expression statements [ "else" statements ] "end".
while_statement = "while" expression statements "end".
return_statement = "@" expression.
assignment = ident "=" expression.
function_call = ident "[" [ expression_list ] "]".