value

value(p: Parser, x: *, m?: string): Parser

Applies a parser and, if it succeeds, returns another value.

x can be anything, so value is one of the few combinators that can return something other than a string.

value(p, x) is an optimized implementation of chain(p, () => always(x)).

Example

const parser = value(string('""'), '"')

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

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

In this example, if the parser string('""') succeeds, then value returns a single character ("). This parser could be used for detecting a quote inside a quoted string in CSV, for instance, where quotation marks are escaped by doubling them.

Parameters

• p: The parser that gets applied to the input.
• x: The value for value to return if p succeeds.
• m: The optional expected error message that will take the place of the default error message.

Success

• Succeeds if p succeeds. In this case, the result of p is discarded and x is returned instead.

Failure

• Fails if p fails.

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
• always