spec.ebnf

program = {functiondef | vardef, ";"};

vardef = "var", id, ":", type, ["=", expr];

funcdef = "func", id, "(", [formal params], ")", [":", type], block;
formalparams = id, ":", type, {",", id, ":", type};

block = "{", {stmt}, "}";
stmt = funccall, ";"
     | vardef, ";"
     | assignment, ";"
     | return, ";"
     | break, ";"
     | continue, ";"
     | if
     | while
     | for;

funccall = id, "(", [actualparams], ")";
actualparams = expr, {",", expr};

assignment = id, "=", expr | id, "+=", expr | id, "-=", expr
           | id, "*=", expr | id, "/=", expr | id, "%=", expr;

if = "if", expr, block, {"else if", block}, ["else", block];
while = "while", expr, block;
for = "for", id, [":", type], "=", expr, ",", expr, [",", expr], block
    | "for", id, [":", type], "in", expr, block;

return = "return", expr
       | "return";
break = "break";
continue = "continue";

id = (letter | "_"), {letter | digit | "_"};
expr = id | expr, binop, expr | unop, expr | number | string
     | "(", expr, ")" | funccall;
type = "integer" | "string";
number = digit, {digit};
binop = "==" | "<" | ">" | "<=" | ">=" | "!=" | "and" | "or" | "xor"
      | "+" | "-" | "*" | "/" | "**" | "%" | "&" | "|" | "^" | "~";
unop = "-" | "not" | "!";
string = '"', printablechar - '"', '"';