PipeEnd Printer

[JaapWijnen]

Hi! Was wondering if PipeEnd can be made a printer in some (maybe all?) cases.
I have the following parser that fails to compile with the following errors:
Generic struct 'ParsePrint' requires that 'Parsers.PipeEnd<Substring.UTF8View>' conform to 'ParserPrinter'
Initializer 'init(with:)' requires that 'Parsers.PipeEnd<Substring.UTF8View>' conform to 'ParserPrinter'

let testParser = ParsePrint {
    Prefix(1...) { $0 != .init(ascii: ">") }.pipe {
        PrefixUpTo("_".utf8)
        "_".utf8
        PrefixUpTo("_".utf8)
        "_".utf8
        PrefixUpTo("/".utf8)
        "/".utf8
    }
}

It can be fixed with the following workaround:

let testParser = ParsePrint {
    Prefix(1...) { $0 != .init(ascii: ">") }.map(.substring).pipe {
        From(.utf8) {
            PrefixUpTo("_".utf8)
            "_".utf8
            PrefixUpTo("/".utf8)
            "/".utf8
        }
    }
}

However I don't immediately see why PipeEnd can't be a printer. A (perhaps naive) PipeEnd printer implementation fixes it:

extension Parsers.PipeEnd: ParserPrinter
{
    @inlinable
    public func print(_ output: (), into input: inout Input) throws { }
}

I might be missing a more subtle case where this fails however. Otherwise I'd be glad to make a PR.

[stephencelis]

@JaapWijnen I think this is an oversight (we've found we reach for map with conversions more often than pipe). If you'd like to PR, the implementation should probably be the exact same as End's printer conformance.

[JaapWijnen]

You can't pass a parser as a conversion can you? (just confused by "reaching for map more often than pipe" for a second)

[JaapWijnen]

The PR is up!