empty

empty(p: Parser, m?: string): Parser

Applies a parser and succeeds if that parser succeeds but does not return a result. If the parser does return a result, empty will fail.

This parser cannot produce a useful error message automatically. To provide a custom message, pass an expected error message in as the second argument.

Example

const parser = empty(opt(char('+')))

const s = parse(parser, '123')
console.log(status(s))  // "ok"
console.log(success(s)) // null

const f = parse(parser, '+123')
console.log(status(f))  // "fail"
console.log(failure(f)) // Parse error at (line 1, column 1):
                        //
                        // +123
                        // ^
                        // Unknown error(s)

Parameters

• p: The parser to be applied. empty fails if this p succeeds but produces a result.
• m: The optional expected message that will be added if empty fails.

Success

• Succeeds if p succeeds but doesn't return a result.

Failure

• Fails if p fails.
• Fails if p succeeds but returns a result.

Fatal Failure

• Fails fatally if p fails fatally.

Throws

• Throws an error if p is not a parser.
• Throws an error if m exists and is not a string.

See Also

• Parser
• not