-
Notifications
You must be signed in to change notification settings - Fork 51
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
This parser builds a radix tree from non empty string alternatives. Radix trees are interesting as they allow for efficient parsing of string alterntives (e.g. enum names) without backtracing and require only 1 character lookahead. String alternatives are first sorted and then grouped by common non empty prefix. Grouped string are then recursively grouped with the same process. In the resulting tree, each group of substrings start with a different character, which can be used to decide which alternative branch to take. This operator is inspired by fastparse `stringIn` one, and requires all alternatives to be non empty.
- Loading branch information
Showing
3 changed files
with
160 additions
and
6 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,97 @@ | ||
| /* | ||
| * Copyright (c) 2020 Typelevel | ||
| * | ||
| * Permission is hereby granted, free of charge, to any person obtaining a copy of | ||
| * this software and associated documentation files (the "Software"), to deal in | ||
| * the Software without restriction, including without limitation the rights to | ||
| * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of | ||
| * the Software, and to permit persons to whom the Software is furnished to do so, | ||
| * subject to the following conditions: | ||
| * | ||
| * The above copyright notice and this permission notice shall be included in all | ||
| * copies or substantial portions of the Software. | ||
| * | ||
| * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | ||
| * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS | ||
| * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR | ||
| * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER | ||
| * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN | ||
| * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. | ||
| */ | ||
|
|
||
| package cats.parse | ||
|
|
||
| import cats.data.NonEmptyList | ||
|
|
||
| import scala.annotation.tailrec | ||
|
|
||
| class RadixNode(val children: Map[Char, (String, RadixNode)], val word: Boolean) { | ||
| override def toString(): String = s"RadixNode($children, $word)" | ||
| } | ||
|
|
||
| object RadixNode { | ||
| def fromSortedStrings(strings: NonEmptyList[String]): RadixNode = { | ||
| @tailrec | ||
| def groupByNonEmptyPrefix( | ||
| keys: List[String], | ||
| prefix: String, | ||
| current: NonEmptyList[String], | ||
| acc: Map[String, NonEmptyList[String]] | ||
| ): Map[String, NonEmptyList[String]] = | ||
| keys match { | ||
| case key :: keys => | ||
| val prefixSize = commonPrefix(prefix, key) | ||
| if (prefixSize == 0) { | ||
| // no common prefix, group current suffixes together sorted again | ||
| groupByNonEmptyPrefix( | ||
| keys, | ||
| key, | ||
| NonEmptyList.one(key), | ||
| acc.updated(prefix, current.map(_.drop(prefix.size)).reverse) | ||
| ) | ||
| } else { | ||
| // clip the prefix to the length, and continue | ||
| groupByNonEmptyPrefix(keys, prefix.take(prefixSize), key :: current, acc) | ||
| } | ||
| case Nil => | ||
| acc.updated(prefix, current.map(_.drop(prefix.size)).reverse) | ||
| } | ||
| NonEmptyList.fromList(strings.filter(_.nonEmpty)) match { | ||
| case Some(nonEmpty) => | ||
| val grouped = | ||
| groupByNonEmptyPrefix( | ||
| nonEmpty.tail, | ||
| nonEmpty.head, | ||
| NonEmptyList.one(strings.head), | ||
| Map.empty | ||
| ).view.mapValues(fromSortedStrings(_)) | ||
| new RadixNode( | ||
| grouped.map { case (k, v) => | ||
| (k(0), (k, v)) | ||
| }.toMap, | ||
| nonEmpty.size < strings.size | ||
| ) | ||
| case None => | ||
| leaf | ||
| } | ||
| } | ||
|
|
||
| private val leaf = new RadixNode(Map.empty, true) | ||
|
|
||
| private def commonPrefix(s1: String, s2: String): Int = { | ||
| @tailrec | ||
| def loop(idx: Int): Int = | ||
| if (idx >= s1.size || idx >= s2.size) { | ||
| idx | ||
| } else { | ||
| val c1 = s1(idx) | ||
| val c2 = s2(idx) | ||
| if (c1 == c2) { | ||
| loop(idx + 1) | ||
| } else { | ||
| idx | ||
| } | ||
| } | ||
| loop(0) | ||
| } | ||
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters