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extern crate peg;
peg::parser!( grammar parse() for str {
pub rule dec_byte() -> u8
= match_str:$(['0'..='9']*<,3>) {?
let val: u64 = match_str.parse().unwrap();
// only let this rule match if the value is in range 0..255
if val <= 255 {
Ok(val as u8)
} else {
// the message explains what the rule expected and is used in the parse error
Err("decimal byte")
}
}
rule tag() -> &'input str
= $(['a'..='z']+)
pub rule xml()
= "<" open:tag() ">" xml()* "</" close:tag() ">" {?
if open == close {
Ok(())
} else {
// TODO this has to be a `&'static str`, so we can't use a dynamic string
Err("matching close tag")
}
}
pub rule return_early() -> i32 = vs:$([_]+) {?
let v = vs.parse::<i32>().map_err(|_| "number")?;
if v > 100 {
return Err("smaller number");
}
Ok(v)
}
});
fn main() {
assert_eq!(parse::dec_byte("0"), Ok(0));
assert_eq!(parse::dec_byte("255"), Ok(255));
assert_eq!(parse::dec_byte("1"), Ok(1));
assert!(parse::dec_byte("256").is_err());
assert!(parse::dec_byte("1234").is_err());
assert!(parse::xml("<a></a>").is_ok());
assert!(parse::xml("<a><b></b><c></c></a>").is_ok());
assert!(parse::xml("<a><b><c></b></c></a>").is_err());
assert!(parse::xml("<a><b></c><c></b></a>").is_err());
assert!(parse::return_early("a").unwrap_err().expected.tokens().any(|e| e == "number"));
assert!(parse::return_early("123").unwrap_err().expected.tokens().any(|e| e == "smaller number"));
assert_eq!(parse::return_early("99").unwrap(), 99);
}
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