init

.gitattributes

@@ -0,0 +1,12 @@
+#
+# https://help.github.com/articles/dealing-with-line-endings/
+#
+# Linux start script should use lf
+/gradlew        text eol=lf
+
+# These are Windows script files and should use crlf
+*.bat           text eol=crlf
+
+# Binary files should be left untouched
+*.jar           binary
+

.gitignore

@@ -0,0 +1,5 @@
+# Ignore Gradle project-specific cache directory
+.gradle
+
+# Ignore Gradle build output directory
+build

GEMINI.md

@@ -0,0 +1,2 @@
+이 프로젝트는 regex 엔진을 처음부터 만들어 보는 프로젝트입니다.
+

gradle.properties

@@ -0,0 +1,5 @@
+# This file was generated by the Gradle 'init' task.
+# https://docs.gradle.org/current/userguide/build_environment.html#sec:gradle_configuration_properties
+
+org.gradle.configuration-cache=true
+

gradle/libs.versions.toml

@@ -0,0 +1,15 @@
+# This file was generated by the Gradle 'init' task.
+# https://docs.gradle.org/current/userguide/platforms.html#sub::toml-dependencies-format
+
+[versions]
+commons-math3 = "3.6.1"
+guava = "33.4.5-jre"
+junit-jupiter-engine = "5.12.1"
+
+[libraries]
+commons-math3 = { module = "org.apache.commons:commons-math3", version.ref = "commons-math3" }
+guava = { module = "com.google.guava:guava", version.ref = "guava" }
+junit-jupiter-engine = { module = "org.junit.jupiter:junit-jupiter-engine", version.ref = "junit-jupiter-engine" }
+
+[plugins]
+kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version = "2.1.20" }

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.2-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradlew

@@ -0,0 +1,251 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/HEAD/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s\n' "$PWD" ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH="\\\"\\\""
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        -jar "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,94 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" -jar "%APP_HOME%\gradle\wrapper\gradle-wrapper.jar" %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

lib/build.gradle.kts

@@ -0,0 +1,56 @@
+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * This generated file contains a sample Kotlin library project to get you started.
+ * For more details on building Java & JVM projects, please refer to https://docs.gradle.org/8.14.2/userguide/building_java_projects.html in the Gradle documentation.
+ */
+
+plugins {
+    // Apply the org.jetbrains.kotlin.jvm Plugin to add support for Kotlin.
+    alias(libs.plugins.kotlin.jvm)
+
+    // Apply the java-library plugin for API and implementation separation.
+    `java-library`
+}
+
+repositories {
+    // Use Maven Central for resolving dependencies.
+    mavenCentral()
+}
+
+dependencies {
+    // Use the Kotlin JUnit 5 integration.
+    testImplementation("org.jetbrains.kotlin:kotlin-test-junit5")
+
+    // Use the JUnit 5 integration.
+    testImplementation(libs.junit.jupiter.engine)
+
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+
+    // This dependency is exported to consumers, that is to say found on their compile classpath.
+    api(libs.commons.math3)
+
+    // This dependency is used internally, and not exposed to consumers on their own compile classpath.
+    implementation(libs.guava)
+    implementation("com.github.h0tk3y.betterParse:better-parse:0.4.4")
+}
+
+// Apply a specific Java toolchain to ease working on different environments.
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+tasks.named<Test>("test") {
+    // Use JUnit Platform for unit tests.
+    useJUnitPlatform()
+}
+
+tasks.withType<Test>{
+    this.testLogging {
+        events("passed", "skipped", "failed")
+        showStandardStreams = true
+        exceptionFormat = org.gradle.api.tasks.testing.logging.TestExceptionFormat.FULL
+    }
+}

lib/src/main/kotlin/org/example/Lexer.kt

@@ -0,0 +1,22 @@
+package org.example
+
+import com.github.h0tk3y.betterParse.lexer.DefaultTokenizer
+import com.github.h0tk3y.betterParse.lexer.Token
+import com.github.h0tk3y.betterParse.lexer.literalToken
+import com.github.h0tk3y.betterParse.lexer.regexToken
+
+
+object RegexLexer {
+    val char = regexToken("[a-zA-Z0-9]")
+    val plus = literalToken("+")
+    val star = literalToken("*")
+    val question = literalToken("?")
+    val dot = literalToken(".")
+    val openParen = literalToken("(")
+    val closeParen = literalToken(")")
+    val alternation = literalToken("|")
+
+    val tokenizer = DefaultTokenizer(
+        listOf(char, plus, star, question, dot, openParen, closeParen, alternation)
+    )
+}

lib/src/main/kotlin/org/example/Library.kt

@@ -0,0 +1,10 @@
+/*
+ * This source file was generated by the Gradle 'init' task
+ */
+package org.example
+
+class Library {
+    fun someLibraryMethod(): Boolean {
+        return true
+    }
+}

lib/src/main/kotlin/org/example/Parser.kt

@@ -0,0 +1,50 @@
+package org.example
+
+import com.github.h0tk3y.betterParse.combinators.*
+import com.github.h0tk3y.betterParse.grammar.Grammar
+import com.github.h0tk3y.betterParse.grammar.parser
+import com.github.h0tk3y.betterParse.lexer.literalToken
+import com.github.h0tk3y.betterParse.lexer.regexToken
+import com.github.h0tk3y.betterParse.parser.Parser
+
+class RegexParser : Grammar<RegexItem>() {
+  val postfixOperator by regexToken("[+*?]")
+  val alternationSymbol by literalToken("|")
+  val openParenSymbol by literalToken("(")
+  val closeParenSymbol by literalToken(")")
+
+  val dot by literalToken(".")
+  val charToken by regexToken("[a-zA-Z0-9]")
+
+  val char by charToken map { CharItem(it.text) }
+
+  val item: Parser<RegexItem> by
+          char or
+                  (dot asJust DotItem()) or
+                  (skip(openParenSymbol) and (parser(::rootParser)) and skip(closeParenSymbol))
+
+  val term: Parser<RegexItem> by
+          (item and optional(postfixOperator)) map
+                  { result ->
+                    result.t1.let { first ->
+                      result.t2?.let {
+                        when (it.text) {
+                          "+" -> PlusItem(first)
+                          "*" -> StarItem(first)
+                          "?" -> QuestionItem(first)
+                          else -> first
+                        }
+                      }
+                              ?: first
+                    }
+                  }
+  val andThen: Parser<RegexItem> by
+          oneOrMore(term) map { items -> items.reduce { left, right -> AndThenItem(left, right) } }
+  val termWithAlternation: Parser<RegexItem> by
+          leftAssociative(
+                  andThen,
+                  alternationSymbol,
+          ) { left, _, right -> AlternationItem(left, right) }
+
+  override val rootParser: Parser<RegexItem> by termWithAlternation
+}

lib/src/main/kotlin/org/example/RegexItem.kt

@@ -0,0 +1,160 @@
+package org.example
+
+data class State(
+        val matched: String,
+        val remaining: String,
+)
+
+data class AvailableState(val seq: Sequence<State> = emptySequence()) : Sequence<State> by seq {
+  val isEmpty: Boolean
+    get() = seq.none()
+}
+
+class MatchResult(val available: AvailableState) {
+
+  val isSuccess: Boolean
+    get() = !this.available.isEmpty
+
+  val isFailure: Boolean
+    get() = this.available.isEmpty
+
+  override fun toString(): String {
+    return if (isSuccess) {
+      "MatchResult(success)"
+    } else {
+      "MatchResult(failure)"
+    }
+  }
+}
+
+// 재귀 하향 분석기.
+interface RegexItem {
+  override fun toString(): String
+  fun findMatch(item: String): AvailableState
+}
+
+fun RegexItem.match(item: String): MatchResult {
+  // 기본 매칭 함수. AvailableState를 MatchResult로 변환
+  return MatchResult(this.findMatch(item))
+}
+
+class AndThenItem(val left: RegexItem, val right: RegexItem) : RegexItem {
+  override fun toString(): String = "${left}${right}"
+  override fun findMatch(item: String): AvailableState {
+    val leftMatch = left.findMatch(item)
+    if (leftMatch.isEmpty) {
+      return AvailableState() // If left match fails, return empty sequence
+    }
+    // If left match is successful, try to match the right item with the remaining string
+    // from the left match.
+
+    return AvailableState(
+            leftMatch.flatMap { state ->
+              val rightMatch = right.findMatch(state.remaining)
+              if (!rightMatch.isEmpty) {
+                // If right match is successful, combine the matched parts
+                rightMatch.map { rightState ->
+                  State(state.matched + rightState.matched, rightState.remaining)
+                }
+              } else {
+                // If right match fails, return an empty sequence
+                sequenceOf()
+              }
+            }
+    )
+  }
+}
+
+class CharItem(val value: String) : RegexItem {
+  override fun toString(): String = value
+  override fun findMatch(item: String): AvailableState {
+    return if (item.isNotEmpty() && item[0].toString() == value) {
+      // If the first character matches, return a successful match
+      AvailableState(sequenceOf(State(value, item.substring(1))))
+    } else {
+      // If it doesn't match, return an empty sequence
+      AvailableState()
+    }
+  }
+}
+
+class PlusItem(val item: RegexItem) : RegexItem {
+  override fun toString(): String = "${item}+"
+  override fun findMatch(item: String): AvailableState {
+    // 욕심쟁이 매칭해야 함. 그래서 가능한 한 많이 매칭해야 함.
+    val results = mutableListOf<State>()
+    var remaining = item
+
+    while (true) {
+      val matchResult = this.item.findMatch(remaining)
+      if (matchResult.isEmpty) {
+        break // No more matches possible
+      }
+      matchResult.forEach { state -> results.add(State(state.matched, state.remaining)) }
+      remaining = matchResult.first().remaining // Update remaining string
+    }
+
+    return AvailableState(results.reversed().asSequence()) // Return all successful matches
+  }
+}
+
+class StarItem(val item: RegexItem) : RegexItem {
+  override fun toString(): String = "${item}*"
+  override fun findMatch(item: String): AvailableState {
+    // 욕심쟁이 매칭해야 함. 그래서 가능한 한 많이 매칭해야 함.
+    val results = mutableListOf<State>(State("", item)) // Start with an empty match
+    var remaining = item
+    while (true) {
+      val matchResult = this.item.findMatch(remaining)
+      if (matchResult.isEmpty) {
+        break // No more matches possible
+      }
+      matchResult.forEach { state -> results.add(State(state.matched, state.remaining)) }
+      remaining = matchResult.first().remaining // Update remaining string
+      if (remaining.isEmpty()) {
+        break // If remaining string is empty, stop matching
+      }
+    }
+    // 반드시 reverse해서 가장 긴 매칭부터 시작해야 함.
+    return AvailableState(results.reversed().asSequence()) // Return all successful matches
+  }
+}
+
+class QuestionItem(val item: RegexItem) : RegexItem {
+  override fun toString(): String = "${item}?"
+  override fun findMatch(item: String): AvailableState {
+    // ?는 0개 또는 1개 매칭을 의미하므로, 먼저 시도해보고 실패하면 빈 시퀀스를 반환
+    val matchResult = this.item.findMatch(item)
+    if (matchResult.isEmpty) {
+      // If the item does not match, return an empty sequence
+      return AvailableState(sequenceOf(State("", item)))
+    }
+    // If it matches, return the successful match
+    return AvailableState(matchResult.map { State(it.matched, it.remaining) })
+  }
+}
+
+class DotItem : RegexItem {
+  override fun toString(): String = "."
+  override fun findMatch(item: String): AvailableState {
+    // .은 임의의 한 문자와 매칭되므로, 첫 문자가 존재하면 매칭 성공
+    return if (item.isNotEmpty()) {
+      AvailableState(sequenceOf(State(item[0].toString(), item.substring(1))))
+    } else {
+      AvailableState() // 빈 문자열에 대해서는 매칭 실패
+    }
+  }
+}
+
+class AlternationItem(val left: RegexItem, val right: RegexItem) : RegexItem {
+  override fun toString(): String = "(${left}|${right})"
+  override fun findMatch(item: String): AvailableState {
+    // Alternation은 왼쪽 또는 오른쪽 항목 중 하나와 매칭되므로, 각각 시도해보고 성공하는 경우를 반환
+    val leftMatch = left.findMatch(item)
+    val rightMatch = right.findMatch(item)
+
+    return AvailableState(
+        (leftMatch + rightMatch).asSequence() // 두 매칭 결과를 합쳐서 반환
+    )
+  }
+}

lib/src/test/kotlin/org/example/LexerTest.kt

@@ -0,0 +1,100 @@
+package org.example
+
+import com.github.h0tk3y.betterParse.lexer.TokenMatch
+import com.github.h0tk3y.betterParse.lexer.DefaultTokenizer
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class LexerTest {
+
+    @Test
+    fun testSimpleCharacter() {
+        val input = "a"
+        val tokens = RegexLexer.tokenizer.tokenize(input).toList()
+        assertEquals(1, tokens.size)
+        assertEquals(RegexLexer.char, tokens[0].type)
+        assertEquals("a", tokens[0].text)
+    }
+
+    @Test
+    fun testCharacterWithPlus() {
+        val input = "a+"
+        val tokens = RegexLexer.tokenizer.tokenize(input).toList()
+        assertEquals(2, tokens.size)
+        assertEquals(RegexLexer.char, tokens[0].type)
+        assertEquals("a", tokens[0].text)
+        assertEquals(RegexLexer.plus, tokens[1].type)
+        assertEquals("+", tokens[1].text)
+    }
+
+    @Test
+    fun testCharacterWithStar() {
+        val input = "b*"
+        val tokens = RegexLexer.tokenizer.tokenize(input).toList()
+        assertEquals(2, tokens.size)
+        assertEquals(RegexLexer.char, tokens[0].type)
+        assertEquals("b", tokens[0].text)
+        assertEquals(RegexLexer.star, tokens[1].type)
+        assertEquals("*", tokens[1].text)
+    }
+
+    @Test
+    fun testCharacterWithQuestion() {
+        val input = "c?"
+        val tokens = RegexLexer.tokenizer.tokenize(input).toList()
+        assertEquals(2, tokens.size)
+        assertEquals(RegexLexer.char, tokens[0].type)
+        assertEquals("c", tokens[0].text)
+        assertEquals(RegexLexer.question, tokens[1].type)
+        assertEquals("?", tokens[1].text)
+    }
+
+    @Test
+    fun testDot() {
+        val input = "."
+        val tokens = RegexLexer.tokenizer.tokenize(input).toList()
+        assertEquals(1, tokens.size)
+        assertEquals(RegexLexer.dot, tokens[0].type)
+        assertEquals(".", tokens[0].text)
+    }
+
+    @Test
+    fun testParentheses() {
+        val input = "(d)"
+        val tokens = RegexLexer.tokenizer.tokenize(input).toList()
+        assertEquals(3, tokens.size)
+        assertEquals(RegexLexer.openParen, tokens[0].type)
+        assertEquals("(", tokens[0].text)
+        assertEquals(RegexLexer.char, tokens[1].type)
+        assertEquals("d", tokens[1].text)
+        assertEquals(RegexLexer.closeParen, tokens[2].type)
+        assertEquals(")", tokens[2].text)
+    }
+
+    @Test
+    fun testAlternation() {
+        val input = "e|f"
+        val tokens = RegexLexer.tokenizer.tokenize(input).toList()
+        assertEquals(3, tokens.size)
+        assertEquals(RegexLexer.char, tokens[0].type)
+        assertEquals("e", tokens[0].text)
+        assertEquals(RegexLexer.alternation, tokens[1].type)
+        assertEquals("|", tokens[1].text)
+        assertEquals(RegexLexer.char, tokens[2].type)
+        assertEquals("f", tokens[2].text)
+    }
+
+    @Test
+    fun testComplexPattern() {
+        val input = "(a|b)*c+"
+        val tokens = RegexLexer.tokenizer.tokenize(input).toList()
+        assertEquals(8, tokens.size)
+        assertEquals(RegexLexer.openParen, tokens[0].type)
+        assertEquals(RegexLexer.char, tokens[1].type)
+        assertEquals(RegexLexer.alternation, tokens[2].type)
+        assertEquals(RegexLexer.char, tokens[3].type)
+        assertEquals(RegexLexer.closeParen, tokens[4].type)
+        assertEquals(RegexLexer.star, tokens[5].type)
+        assertEquals(RegexLexer.char, tokens[6].type)
+    }
+}

lib/src/test/kotlin/org/example/LibraryTest.kt

@@ -0,0 +1,14 @@
+/*
+ * This source file was generated by the Gradle 'init' task
+ */
+package org.example
+
+import kotlin.test.Test
+import kotlin.test.assertTrue
+
+class LibraryTest {
+    @Test fun someLibraryMethodReturnsTrue() {
+        val classUnderTest = Library()
+        assertTrue(classUnderTest.someLibraryMethod(), "someLibraryMethod should return 'true'")
+    }
+}

lib/src/test/kotlin/org/example/ParserTest.kt

@@ -0,0 +1,110 @@
+package org.example
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import com.github.h0tk3y.betterParse.grammar.parseToEnd
+
+class ParserTest {
+
+    @Test
+    fun testSimpleCharacter() {
+        val input = "a"
+        val result = RegexParser().parseToEnd(input)
+        assertEquals("a",result.toString())
+    }
+    @Test
+    fun testCharacterWithPlus() {
+        val input = "a+"
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals("a+", result.toString())
+        assert(result.match("a").isSuccess)
+        assert(result.match("aa").isSuccess)
+        assert(!result.match("b").isSuccess)
+    }
+    @Test
+    fun testCharacterWithStar() {
+        val input = "b*"
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals("b*", result.toString())
+        assert(result.match("").isSuccess)
+        assert(result.match("b").isSuccess)
+        assert(result.match("bb").isSuccess)
+        assert(result.match("a").isSuccess)
+    }
+    @Test
+    fun testCharacterWithQuestion() {
+        val input = "c?"
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals("c?", result.toString())
+        assert(result.match("").isSuccess)
+        assert(result.match("c").isSuccess)
+        assert(result.match("cc").isSuccess)
+    }
+    @Test
+    fun testDot() {
+        val input = "."
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals(".", result.toString())
+        assert(result.match("a").isSuccess)
+        assert(result.match("1").isSuccess)
+        assert(!result.match("").isSuccess)
+    }
+
+    @Test
+    fun testAlternation() {
+        val input = "a|b"
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals("(a|b)", result.toString())
+        assert(result.match("a").isSuccess)
+        assert(result.match("b").isSuccess)
+        assert(!result.match("c").isSuccess)
+    }
+    @Test
+    fun testParentheses() {
+        val input = "(d)"
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals("d", result.toString())
+        assert(result.match("d").isSuccess)
+        assert(!result.match("e").isSuccess)
+    }
+
+    @Test
+    fun testComplexExpression() {
+        val input = "a(b|c)*d+"
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals("a(b|c)*d+", result.toString())
+        assert(result.match("ad").isSuccess)
+        assert(!result.match("ab").isSuccess)
+        assert(result.match("acd").isSuccess)
+        assert(result.match("abbbd").isSuccess)
+        assert(!result.match("a").isSuccess)
+        assert(!result.match("b").isSuccess)
+    }
+    @Test
+    fun testAndThen() {
+        val input = "ab"
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals("ab", result.toString())
+        assert(result.match("ab").isSuccess)
+        assert(!result.match("a").isSuccess)
+        assert(!result.match("b").isSuccess)
+    }
+    @Test
+    fun testDotAndPlus() {
+        val input = ".+a";
+        val parser = RegexParser()
+        val result = parser.parseToEnd(input)
+        assertEquals(".+a", result.toString())
+        assert(!result.match("a").isSuccess)
+        assert(result.match("ba").isSuccess)
+        assert(result.match("bca").isSuccess)
+    }
+}

settings.gradle.kts

@@ -0,0 +1,14 @@
+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * The settings file is used to specify which projects to include in your build.
+ * For more detailed information on multi-project builds, please refer to https://docs.gradle.org/8.14.2/userguide/multi_project_builds.html in the Gradle documentation.
+ */
+
+plugins {
+    // Apply the foojay-resolver plugin to allow automatic download of JDKs
+    id("org.gradle.toolchains.foojay-resolver-convention") version "0.10.0"
+}
+
+rootProject.name = "regex"
+include("lib")