initial commit

Author: p-ja

.editorconfig

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+# EditorConfig helps maintain consistent coding styles across different editors
+# https://editorconfig.org
+
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.java]
+indent_style = space
+indent_size = 4
+max_line_length = 120
+ij_continuation_indent_size = 8
+
+[*.xml]
+indent_style = space
+indent_size = 4
+
+[*.{md,markdown}]
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = false
+
+[*.{yml,yaml}]
+indent_style = space
+indent_size = 2
+
+[*.properties]
+indent_style = space
+indent_size = 4
+
+[{pom.xml,settings.xml}]
+indent_style = space
+indent_size = 4

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches:
+      - main
+      - 'feature/**'
+      - 'bugfix/**'
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Read Java version from .sdkmanrc
+        id: sdkman
+        run: |
+          JAVA_VERSION=$(grep "^java=" .sdkmanrc | cut -d'=' -f2 | cut -d'-' -f1)
+          echo "version=$JAVA_VERSION" >> $GITHUB_OUTPUT
+
+      - name: Set up JDK from .sdkmanrc
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: ${{ steps.sdkman.outputs.version }}
+
+      - name: Build with Maven Wrapper
+        run: ./mvnw clean verify --batch-mode

.github/workflows/release.yml

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+name: Manual Release
+
+on:
+  workflow_dispatch:
+    inputs:
+      new_version:
+        description: 'New version (e.g., 1.2.0)'
+        required: true
+      release_name:
+        description: 'Release name'
+        required: true
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          fetch-depth: 0
+
+      - name: Check if tag already exists
+        run: |
+          if git rev-parse "v${{ github.event.inputs.new_version }}" >/dev/null 2>&1; then
+            echo "Error: Tag v${{ github.event.inputs.new_version }} already exists. Releases are immutable."
+            exit 1
+          fi
+
+      - name: Read Java version from .sdkmanrc
+        id: sdkman
+        run: |
+          JAVA_VERSION=$(grep "^java=" .sdkmanrc | cut -d'=' -f2 | cut -d'-' -f1)
+          echo "version=$JAVA_VERSION" >> $GITHUB_OUTPUT
+
+      - name: Set up JDK from .sdkmanrc
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: ${{ steps.sdkman.outputs.version }}
+          server-id: central
+          server-username: MAVEN_USERNAME
+          server-password: MAVEN_PASSWORD
+          gpg-private-key: ${{ secrets.GPG_PRIVATE_KEY }}
+          gpg-passphrase: MAVEN_GPG_PASSPHRASE
+
+      - name: Configure Git
+        run: |
+          git config user.name "${{ github.actor }}"
+          git config user.email "${{ github.actor }}@users.noreply.github.com"
+
+      - name: Update Version Files
+        run: |
+          ./mvnw versions:set -DnewVersion=${{ github.event.inputs.new_version }} -DgenerateBackupPoms=false --batch-mode
+          ./mvnw versions:commit --batch-mode
+
+          sed -i '/either<\/artifactId>/,/<version>/ s/<version>[^<]*<\/version>/<version>${{ github.event.inputs.new_version }}<\/version>/' README.md
+
+          git add pom.xml README.md
+          git diff --staged --quiet || git commit -m "Bump version to ${{ github.event.inputs.new_version }}"
+          git push origin main
+
+      - name: Build and Deploy to Maven Central
+        run: ./mvnw clean deploy -Prelease --batch-mode
+        env:
+          MAVEN_USERNAME: ${{ secrets.CENTRAL_TOKEN_USERNAME }}
+          MAVEN_PASSWORD: ${{ secrets.CENTRAL_TOKEN_PASSWORD }}
+          MAVEN_GPG_PASSPHRASE: ${{ secrets.GPG_PASSPHRASE }}
+
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v1
+        with:
+          tag_name: v${{ github.event.inputs.new_version }}
+          name: ${{ github.event.inputs.release_name }}
+          files: target/*.jar
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.gitignore

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+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+.kotlin
+
+### IntelliJ IDEA ###
+.idea/
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store
+
+### Windows ###
+Thumbs.db
+
+### Logs ###
+*.log
+
+### Temporary files ###
+*.tmp
+*.temp
+*~

.mvn/wrapper/maven-wrapper.properties

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+wrapperVersion=3.3.4
+distributionType=only-script
+distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.11/apache-maven-3.9.11-bin.zip

.sdkmanrc

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+# Enable auto-env through the sdkman_auto_env config
+# Add key=value pairs of SDKs to use below
+java=21.0.8-tem

CLAUDE.md

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+# Either - Java Implementation
+
+## Overview
+
+This project provides a Java implementation of Scala's `Either` type, a functional data structure representing a value of one of two possible types (a disjoint union). By convention, `Left` represents failure/error cases and `Right` represents success cases.
+
+## Project Structure
+
+```
+either/
+├── src/main/java/stream/header/
+│   └── Either.java          # Main Either implementation
+├── pom.xml                  # Maven configuration
+└── CLAUDE.md               # This file
+```
+
+## Key Information
+
+- **Language**: Java 17+
+- **Build Tool**: Maven (use `./mvnw` wrapper)
+- **Package**: `stream.header`
+- **Main Class**: `Either<L, R>` (sealed interface with `Left` and `Right` records)
+
+## Either API
+
+### Creation
+```java
+Either<String, Integer> right = Either.right(42);
+Either<String, Integer> left = Either.left("error");
+```
+
+### Core Operations (Right-biased)
+- `map(Function)` - Transform Right value
+- `flatMap(Function)` - Chain Either-returning operations
+- `mapLeft(Function)` - Transform Left value
+- `fold(Function, Function)` - Pattern match on Left or Right
+- `getOrElse(T)` - Extract Right or default value
+- `filterOrElse(Predicate, Supplier)` - Filter Right value
+
+### Querying
+- `isLeft()` / `isRight()` - Check which side
+- `contains(R)` - Check if Right equals value
+- `exists(Predicate)` - Test Right value
+- `getLeft()` / `getRight()` - Unsafe extraction (throws if wrong side)
+
+### Conversion
+- `toOptional()` - Convert Right to Optional
+- `toOptionalLeft()` - Convert Left to Optional
+- `swap()` - Exchange Left and Right
+
+### Side Effects
+- `forEach(Consumer)` - Apply action to Right
+- `forEachLeft(Consumer)` - Apply action to Left
+
+## Build Commands
+
+```bash
+# Compile
+./mvnw compile
+
+# Run tests
+./mvnw test
+
+# Package
+./mvnw package
+
+# Clean
+./mvnw clean
+```
+
+## Design Decisions
+
+1. **Sealed Interface**: Uses Java 17 sealed interfaces for exhaustive pattern matching
+2. **Records**: Left and Right are immutable records
+3. **Right-biased**: All monadic operations (map, flatMap) operate on Right, matching modern Scala behavior
+4. **Null Safety**: Both Left and Right reject null values
+5. **Fail-fast**: Methods validate null parameters immediately
+
+## Usage Example
+
+```java
+import stream.header.Either;
+
+public class Example {
+    public static Either<String, Integer> divide(int a, int b) {
+        if (b == 0) {
+            return Either.left("Division by zero");
+        }
+        return Either.right(a / b);
+    }
+
+    public static void main(String[] args) {
+        Either<String, Integer> result = divide(10, 2)
+            .map(x -> x * 2)
+            .flatMap(x -> divide(x, 5));
+
+        String message = result.fold(
+            error -> "Error: " + error,
+            value -> "Result: " + value
+        );
+
+        System.out.println(message); // "Result: 4"
+    }
+}
+```
+
+## Conventions
+
+- **Left**: Represents errors, failures, or exceptional cases (typically `String`, `Exception`, or custom error types)
+- **Right**: Represents successful results and normal values
+- All operations are right-biased (operate on Right, short-circuit on Left)

LICENSE.txt

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+Copyright (c) 2025 stream.header.either contributors
+
+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.