Given the following EBNF grammar (found on wikipedia for PL/0), what is an expression preceded by the "ODD" keyword? I would like to implement the simple language as a small project but I can not seem to figure out what this means. Has anyone head of this before or able to interpret what an odd expression is so that I can write a compiler for the language correctly?
program = block "." .
block = [ "const" ident "=" number {"," ident "=" number} ";"]
[ "var" ident {"," ident} ";"]
{ "procedure" ident ";" block ";" } statement .
statement = [ ident ":=" expression | "call" ident |
"begin" statement {";" statement } "end" |
"if" condition "then" statement |
"while" condition "do" statement ].
condition = "odd" expression |
expression ("="|"#"|"<"|"<="|">"|">=") expression .
expression = [ "+"|"-"] term { ("+"|"-") term}.
term = factor {("*"|"/") factor}.
factor = ident | number | "(" expression ")".
The EBNF grammar indicates via quotation marks that ODD is a sequence of terminal symbols. This is confirmed by the examples following the grammar on the Wikipedia page. Semantically, it appears to be a predicate testing the parity of numeric values.
BEGIN
a := x;
b := y;
z := 0;
WHILE b > 0 DO BEGIN
IF ODD b THEN z := z + a;
a := 2 * a;
b := b / 2
END
END;