Repository navigation
Only find one match per position #1
Description
Hi, nice library, I especially like the syntax.
Is there any way of parsing only one match per position? Now when I run code like this:
let myany = LazilyRepeating(one() as Wildcard<String>)
let token = Token("." • myany • Literal(" ") • myany • " ")
let parser = myany • token
parser.forwardMatches(enteringFrom: Match<String>(over: #" .1 slkjdf.2 .3 "#)).forEach {
print($0.captures(for: token))
}it seems to find all possible matches for each position:
[".1 "]
[".1 slkjdf.2 "]
[".1 slkjdf.2 .3 "]
[".1 slkjdf.2 .3 "]
[".1 slkjdf.2 "]
[".1 slkjdf.2 .3 "]
[".1 slkjdf.2 .3 "]
[".1 slkjdf.2 .3 "]
[".1 slkjdf.2 .3 "]
[".1 slkjdf.2 .3 "]
[".2 .3 "]
[".2 .3 "]
[".2 .3 "]
[".3 "]
How do I tell LazilyRepeating to only find the shortest possible match?
Activity
ctxppc commentedon Jun 3, 2020
Thanks for your kind words!
I haven’t had much time recently to continue implementing a few more features I had in mind, and especially document a few things! (But I’m definitely planning to!)
Tokenis a pattern class that is supposed to be used at most once in a given pattern. When used on two or more places, it can capture multiple sequences per match but it’s not well-defined. The multiple-captures features is only well-defined when a single token object is used within some kind of repeating pattern (likeLazilyRepeating): in that case it blindly follows the matching semantics of the repeating pattern.I see multiple uses of the token within the pattern. Did you instead mean to use a back-reference, which matches a subsequence that a previous token matched? The read-me mentions
Referencingbut I haven’t gotten around to implementing it yet.LazilyRepeatingalready tries to match its sub-pattern as few times as possible, or in your example, by applying the wildcard zero times, once, twice, thrice, and so. In your example output, it’s the first, second, third, … element.forwardMatches(…)returns a lazily evaluated array for every possible match, so you can just take the first match to get the match with the least repetitions.However,
forwardMatches(enteringFrom:)is a foundational method that returns partial matches (matches that might not cover the whole string yet). Larger patterns build on top of these partial matches. Thematches(over:)method (inPattern) does exclude all partial matches, and is the method for “client use”. :)kareman commentedon Jul 7, 2020
Hi, and sorry about the very late reply. I liked the syntax in this project so much I implemented something similar in my PEG parser at https://github.com/kareman/Patterns . It made the API far easier to work with (as soon as you find out how to type • and ¿ 😄) .
ctxppc commentedon Jul 7, 2020
Looks nice, especially its strong typing and its VM approach! 💯