Issues with whitespace

[fatlazycat]

Doing AoC 2021 I had the input

41 31 12 14 82
 4 97 76 49 15
50 43 72 22 24
53 56 78 33 52
65 68 26  0 94

How would you parse this ?

If I had

41,31,12,14,82
4,97,76,49,15
50,43,72,22,24
53,56,78,33,52
65,68,26,0,94

I would just use for each row

Many(Int.parser(), separator: StartsWith(","))

But unsure where I would start attempting it where you might have leading whitespace.

I looked to explicitly stating Int.parser() with skipping whitespace but can't seem to grasp it, such as

        let parser = Prefix(while: \.isWhitespace)
            .take(Int.parser())
            .skip(Whitespace())
            .take(Int.parser())
            .skip(Whitespace())
            .take(Int.parser())
            .skip(Whitespace())
            .take(Int.parser())
            .skip(Whitespace())
            .take(Int.parser())

Thanks

[iampatbrown]

One way to approach it could be

var input = """
41 31 12 14 82
 4 97 76 49 15
50 43 72 22 24
53 56 78 33 52
65 68 26  0 94
"""[...].utf8

let output = Many(
  Skip(Whitespace())
    .take(Int.parser())
    .skip(Whitespace())
).parse(&input)

[fatlazycat]

Thanks, if you were to just define the parser without giving the type info from the input what you do ?

I'd like to parse each line individually.

[fatlazycat]

Came up with

        let dataSet = Many(PrefixUpTo<Substring>("\n"), separator: "\n").parse(data)!
        let parser = Many(Skip(Whitespace<Substring.UTF8View>()).take(Int.parser()).skip(Whitespace()))
        let result = dataSet.map{ parser.parse($0.utf8) }.map { $0.0! }

My lack of understanding of Strings in Swift seems the main issue 😀

[stephencelis]

Another way of breaking the problem down and staying in Substring:

let spaces = Skip(Prefix(while: { $0 == " " }))
let row = Many(spaces.take(Int.parser()).skip(spaces))
let rows = Many(row, separator: "\n")

[fatlazycat]

Needed todo

        let spaces = Skip(Prefix<Substring>(while: { $0 == " " }))

But that looks nice & clean, thanks

[fatlazycat]

@stephencelis out of interest is there a reason why Whitespace is only for UTF8 ?

[stephencelis]

Whitespace() only consumes ASCII whitespace at the moment. It should probably be spelled ASCII.Whitespace() in the future, which would open up the opportunity for a Whitespace that works with Substring.

[fatlazycat]

@stephencelis See you have released a new version with the aid for type inference. Thanks