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Get range of parsed input #68
Description
Hi,
I am struggling to find a way to get the range of my parsed input and I am not sure whether this is something which would be useful to this library.
For example consider the following use case:
I am writing an ingredient parser and I want to make sense of a string by parsing the ingredient amount and unit. But I also want to highlight the parse amount and unit when displaying the ingredient string in a NSAttributedString. From my understand I would need to know which range the parser combinator parsed.
Here is a simple example:
final class IngredientParser {
func parse(_ ingredients: [String]) -> [Ingredient] {
return ingredients.compactMap {
parseLine($0.trimmingCharacters(in: .whitespacesAndNewlines))
}
}
func parse(_ ingredientsInput: String) -> [Ingredient] {
return parse(ingredientsInput.split(separator: "\n").map { String($0) })
}
private func parseLine(_ ingredientsInput: String) -> Ingredient? {
let amount: AnyParser<Substring.UTF8View, Int> = Int.parser()
.eraseToAnyParser()
let unit: AnyParser<Substring.UTF8View, Unit> = "gram".utf8.map { Unit.gram }.eraseToAnyParser()
let line = Optional.parser(of: amount)
.skip(Whitespace())
.take(Optional.parser(of: unit))
.skip(Whitespace())
.take(Rest())
.map { result -> Ingredient in
return Ingredient(amount: result.0, unit: result.1, name: result.2)
}
var input = ingredientsInput[...].utf8
return line.parse(&input)
}
}Would it be possible to get the parsed range of f.e the Int.parser() from parsing the amount?
Activity
stephencelis commentedon Nov 29, 2021
Hi @dehlen,
One way to capture the range of a parsed result is by introducing a new operator that captures it. Here's something @mbrandonw and I sketched out:
With that defined, you can get the range from
Int.parser()by tacking onwithRange():Hope this helps!
I'm going to convert this to a discussion, since it's not a bug with the library.