Repository: iluwatar/java-design-patterns
Issue: Currying
Labels: epic: pattern
type: feature

I's a functional programming design pattern. As far as I understand you call a function with less parameters than usual and it can be used to defer processing when it has many steps involved.

UML example

```
@startuml
'https://plantuml.com/class-diagram

interface BiFunction <ParamType1, ParamType2, ResultType>{
}

interface Curried<ParamType1, ParamType2 extends Simple> {
  +ParamType2 apply(final ParamType1 a);
}

interface Simple<ParamType1, ParamType2, ResultType> extends BiFunction {
  +ResultType apply(final ParamType1 a, final ParamType2 b);
}

@enduml
```

![image](https://user-images.githubusercontent.com/1063901/136424980-f7ab35e9-5654-419e-8f7d-6a1257e12585.png)

With the curried version you can do stuff like:

```
   System.out.println(curriedAdd.apply(4).apply(5));

    Function1<Integer, Integer> adder5 = curriedAdd.apply(5);
    //some complicate and time consuming process here
    System.out.println(adder5.apply(4));
    System.out.println(adder5.apply(6));

```

Issue comments:
There is a concrete example about currying in Java on Baeldung's website: https://www.baeldung.com/java-currying
hi @iluwatar , can I work on this issue for Hacktoberfest?
Sure @januslinhc, it's now assigned to you
Hey @iluwatar, could I work on this issue?
All right @hkattt, you're free to proceed
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

@hkattt is still working on this

Pull request review comments:
Please implement the yaml frontmatter according to https://github.com/iluwatar/java-design-patterns/wiki/01.-How-to-contribute
Use Lombok to reduce boilerplate
Doesn't look useful

Patch that resolved the issue:
diff --git a/currying/README.md b/currying/README.md
new file mode 100644
index 000000000000..72e0e89d46df
--- /dev/null
+++ b/currying/README.md
@@ -0,0 +1,191 @@
+---
+title: Currying
+category: Functional 
+language: en
+tag:
+- Decoupling
+---
+
+## Name / classification
+Currying
+
+## Intent
+Currying decomposes a function that takes multiple arguments into a sequence of functions that each take a single argument. 
+Curried functions are useful since they can be used to create new functions with lower arity to perform more specialised tasks
+in a concise and readable manner. This is done via partial application.
+
+## Explanation
+Real-world example
+> Consider a librarian who wants to populate their library with books. The librarian wants functions which can create 
+> books corresponding to specific genres and authors. Currying makes this possible by writing a curried book builder 
+> function and utilising partial application.
+
+In plain words
+> Decompose a function that take multiple arguments into multiple functions that take a single argument. 
+
+Wikipedia says
+> Currying is the technique of converting a function that takes multiple arguments into a sequence of functions that
+> each take a single argument. Given a function $f:(X \times Y) \rightarrow Z$, currying constructs a new function 
+> $h:X \rightarrow (Y\rightarrow Z)$. $h$ takes an argument from $X$ and returns a function which maps $Y$ to $Z$. Hence,
+> $h(x)(y) = f(x, y)$.
+
+Programmatic example  
+We have a `Book` class and `Genre` enum.
+```java
+public class Book {
+  private final Genre genre;
+  private final String author;
+  private final String title;
+  private final LocalDate publicationDate;
+
+  Book(Genre genre, String author, String title, LocalDate publicationDate) {
+    this.genre = genre;
+    this.author = author;
+    this.title = title;
+    this.publicationDate = publicationDate;
+  }
+}
+
+public enum Genre {
+  FANTASY,
+  HORROR,
+  SCI_FI;
+}
+```
+We could easily create a `Book` object with the following method:
+```java
+Book createBook(Genre genre, String author, String title, LocalDate publicationDate) {
+    return new Book(genre, author, title, publicationDate);
+}
+```
+However, what if we only wanted to create books from the `FANTASY` genre? We could pass in the `FANTASY` parameter on each method call; however, this is repetitive. We could define a new method specifically for creating `FANTASY` books; however, it is infeasible to create a new method for each book genre. The solution is to create a curried function.
+```java
+static Function<Genre, Function<String, Function<String, Function<LocalDate, Book>>>> book_creator
+      = genre
+      -> author
+      -> title
+      -> publicationDate
+      -> new Book(genre, author, title, publicationDate);
+```
+Note that the order of the parameters is important. `genre` must come before `author`, `author` must come before `title` and so on. We must be considerate of this when writing curried functions to take full advantage of partial application. Using the above function, we can define a new function `fantasyBookFunc`, to generate `FANTASY` books as follows:
+```java
+Function<String, Function<String, Function<LocalDate, Book>>> fantasyBookFunc = Book.book_creator.apply(Genre.FANTASY);
+```
+Unfortunately, the type signature of `BOOK_CREATOR` and `fantasyBookFunc` are difficult to read and understand. We can improve this by using the [builder pattern](https://java-design-patterns.com/patterns/builder/) and [functional interfaces](https://www.geeksforgeeks.org/functional-interfaces-java/#:~:text=A%20functional%20interface%20is%20an,any%20number%20of%20default%20methods). 
+```java
+public static AddGenre builder() {
+    return genre
+        -> author
+        -> title
+        -> publicationDate
+        -> new Book(genre, author, title, publicationDate);
+}
+
+public interface AddGenre {
+Book.AddAuthor withGenre(Genre genre);
+}
+
+public interface AddAuthor {
+Book.AddTitle withAuthor(String author);
+}
+
+public interface AddTitle {
+Book.AddPublicationDate withTitle(String title);
+}
+
+public interface AddPublicationDate {
+Book withPublicationDate(LocalDate publicationDate);
+}
+```
+The semantics of the `builder` function can easily be understood. The `builder` function returns a function `AddGenre`, which adds the genre to the book. Similarity, the `AddGenre` function returns another function `AddTitle`, which adds the title to the book and so on, until the `AddPublicationDate` function returns a `Book`. 
+For example, we could create a `Book` as follows:
+```java
+Book book = Book.builder().withGenre(Genre.FANTAST)
+        .withAuthor("Author")
+        .withTitle("Title")
+        .withPublicationDate(LocalDate.of(2000, 7, 2));
+```
+The below example demonstrates how partial application can be used with the `builder` function to create specialised book builder functions.
+```java
+public static void main(String[] args) {
+    LOGGER.info("Librarian begins their work.");
+    
+    // Defining genre book functions
+    Book.AddAuthor fantasyBookFunc = Book.builder().withGenre(Genre.FANTASY);
+    Book.AddAuthor horrorBookFunc = Book.builder().withGenre(Genre.HORROR);
+    Book.AddAuthor scifiBookFunc = Book.builder().withGenre(Genre.SCI_FI);
+
+    // Defining author book functions
+    Book.AddTitle kingFantasyBooksFunc = fantasyBookFunc.withAuthor("Stephen King");
+    Book.AddTitle kingHorrorBooksFunc = horrorBookFunc.withAuthor("Stephen King");
+    Book.AddTitle rowlingFantasyBooksFunc = fantasyBookFunc.withAuthor("J.K. Rowling");
+
+    // Creates books by Stephen King (horror and fantasy genres)
+    Book shining = kingHorrorBooksFunc.withTitle("The Shining")
+    .withPublicationDate(LocalDate.of(1977, 1, 28));
+    Book darkTower = kingFantasyBooksFunc.withTitle("The Dark Tower: Gunslinger")
+    .withPublicationDate(LocalDate.of(1982, 6, 10));
+
+    // Creates fantasy books by J.K. Rowling
+    Book chamberOfSecrets = rowlingFantasyBooksFunc.withTitle("Harry Potter and the Chamber of Secrets")
+    .withPublicationDate(LocalDate.of(1998, 7, 2));
+
+    // Create sci-fi books
+    Book dune = scifiBookFunc.withAuthor("Frank Herbert")
+    .withTitle("Dune")
+    .withPublicationDate(LocalDate.of(1965, 8, 1));
+    Book foundation = scifiBookFunc.withAuthor("Isaac Asimov")
+    .withTitle("Foundation")
+    .withPublicationDate(LocalDate.of(1942, 5, 1));
+
+    LOGGER.info("Stephen King Books:");
+    LOGGER.info(shining.toString());
+    LOGGER.info(darkTower.toString());
+
+    LOGGER.info("J.K. Rowling Books:");
+    LOGGER.info(chamberOfSecrets.toString());
+
+    LOGGER.info("Sci-fi Books:");
+    LOGGER.info(dune.toString());
+    LOGGER.info(foundation.toString());
+}
+```
+Program output:
+```
+Librarian begins their work.
+Stephen King Books:
+Book{genre=HORROR, author='Stephen King', title='The Shining', publicationDate=1977-01-28}
+Book{genre=FANTASY, author='Stephen King', title='The Dark Tower: Gunslinger', publicationDate=1982-06-10}
+J.K. Rowling Books:
+Book{genre=FANTASY, author='J.K. Rowling', title='Harry Potter and the Chamber of Secrets', publicationDate=1998-07-02}
+Sci-fi Books:
+Book{genre=SCI_FI, author='Frank Herbert', title='Dune', publicationDate=1965-08-01}
+Book{genre=SCI_FI, author='Isaac Asimov', title='Foundation', publicationDate=1942-05-01}
+```
+
+## Class diagram
+![currying-uml](./etc/currying.urm.png)
+
+## Applicability
+A curried function which has only been passed some of its arguments is called a partial application. Partial application 
+allows for the creation of functions with some pre-defined data in their scope, since partial application can be used to
+create specialised functions with lower arity. This abstraction can help keep code readable and concise. Therefore, currying is useful when frequently calling functions with fixed parameters.
+
+## Known uses
+Most functional programming languages support curried functions. A popular example is [Haskell](https://www.haskell.org/), in which all functions are considered curried. 
+
+## Consequences
+Pros
+* Currying allows for partial application, which can be used to create specialised functions concisely.
+
+Cons
+* The order of the parameters in a curried function is important since we want to take advantage of partial application. It is best to input the most general parameters first and input specific parameters last. 
+* As shown in the programmatic example above, curried functions with several parameters have a cumbersome type signature (in Java).
+
+## Related patterns
+* [Builder patter](https://java-design-patterns.com/patterns/builder/)
+
+## Credits
+* [Currying in Java](https://www.baeldung.com/java-currying)
+* [What Is Currying in Programming](https://towardsdatascience.com/what-is-currying-in-programming-56fd57103431#:~:text=Currying%20is%20helpful%20when%20you,concise%2C%20and%20more%20readable%20solution.)
+* [Why the fudge should I use currying?](https://medium.com/dailyjs/why-the-fudge-should-i-use-currying-84e4000c8743)
\ No newline at end of file
diff --git a/currying/etc/currying.urm.puml b/currying/etc/currying.urm.puml
new file mode 100644
index 000000000000..9b336ff90828
--- /dev/null
+++ b/currying/etc/currying.urm.puml
@@ -0,0 +1,39 @@
+@startuml
+package com.iluwatar.currying {
+  class App {
+    + App()
+    + main(args : String[]) {static}
+  }
+  class Book {
+    ~ BOOK_CREATOR : Function<Genre, Function<String, Function<String, Function<LocalDate, Book>>>> {static}
+    - author : String
+    - genre : Genre
+    - publicationDate : LocalDate
+    - title : String
+    ~ Book(genre : Genre, author : String, title : String, publicationDate : LocalDate)
+    + builder() : AddGenre {static}
+  }
+  interface AddAuthor {
+    + withAuthor(String) : AddTitle {abstract}
+  }
+  interface AddGenre {
+    + withGenre(Genre) : AddAuthor {abstract}
+  }
+  interface AddPublicationDate {
+    + withPublicationDate(LocalDate) : Book {abstract}
+  }
+  interface AddTitle {
+    + withTitle(String) : AddPublicationDate {abstract}
+  }
+  enum Genre {
+    + FANTASY {static}
+    + HORROR {static}
+    + SCI_FI {static}
+  }
+}
+Book -->  "-genre" Genre
+AddPublicationDate ..+ Book
+AddAuthor ..+ Book
+AddTitle ..+ Book
+AddGenre ..+ Book
+@enduml
\ No newline at end of file
diff --git a/currying/pom.xml b/currying/pom.xml
new file mode 100644
index 000000000000..5b5385c45a59
--- /dev/null
+++ b/currying/pom.xml
@@ -0,0 +1,66 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+
+    The MIT License
+    Copyright © 2014-2022 Ilkka Seppälä
+
+    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.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.26.0-SNAPSHOT</version>
+    </parent>
+    <artifactId>currying</artifactId>
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+    <build>
+        <plugins>
+            <!-- Maven assembly plugin is invoked with default setting which we have
+        in parent pom and specifying the class having main method -->
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <configuration>
+                            <archive>
+                                <manifest>
+                                    <mainClass>com.iluwatar.currying.App</mainClass>
+                                </manifest>
+                            </archive>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>
\ No newline at end of file
diff --git a/currying/src/main/java/com/iluwatar/currying/App.java b/currying/src/main/java/com/iluwatar/currying/App.java
new file mode 100644
index 000000000000..d3ca262b56c4
--- /dev/null
+++ b/currying/src/main/java/com/iluwatar/currying/App.java
@@ -0,0 +1,86 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * 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 com.iluwatar.currying;
+
+import java.time.LocalDate;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+* Currying decomposes a function with multiple arguments in multiple functions that
+* take a single argument. A curried function which has only been passed some of its
+* arguments is called a partial application. Partial application is useful since it can
+* be used to create specialised functions in a concise way.
+*
+* <p>In this example, a librarian uses a curried book builder function create books belonging to
+* desired genres and written by specific authors.
+*/
+@Slf4j
+public class App {
+  /**
+  * Main entry point of the program.
+  */
+  public static void main(String[] args) {
+    LOGGER.info("Librarian begins their work.");
+
+    // Defining genre book functions
+    Book.AddAuthor fantasyBookFunc = Book.builder().withGenre(Genre.FANTASY);
+    Book.AddAuthor horrorBookFunc = Book.builder().withGenre(Genre.HORROR);
+    Book.AddAuthor scifiBookFunc = Book.builder().withGenre(Genre.SCIFI);
+
+    // Defining author book functions
+    Book.AddTitle kingFantasyBooksFunc = fantasyBookFunc.withAuthor("Stephen King");
+    Book.AddTitle kingHorrorBooksFunc = horrorBookFunc.withAuthor("Stephen King");
+    Book.AddTitle rowlingFantasyBooksFunc = fantasyBookFunc.withAuthor("J.K. Rowling");
+
+    // Creates books by Stephen King (horror and fantasy genres)
+    Book shining = kingHorrorBooksFunc.withTitle("The Shining")
+            .withPublicationDate(LocalDate.of(1977, 1, 28));
+    Book darkTower = kingFantasyBooksFunc.withTitle("The Dark Tower: Gunslinger")
+            .withPublicationDate(LocalDate.of(1982, 6, 10));
+
+    // Creates fantasy books by J.K. Rowling
+    Book chamberOfSecrets = rowlingFantasyBooksFunc.withTitle("Harry Potter and the Chamber of Secrets")
+            .withPublicationDate(LocalDate.of(1998, 7, 2));
+
+    // Create sci-fi books
+    Book dune = scifiBookFunc.withAuthor("Frank Herbert")
+            .withTitle("Dune")
+            .withPublicationDate(LocalDate.of(1965, 8, 1));
+    Book foundation = scifiBookFunc.withAuthor("Isaac Asimov")
+            .withTitle("Foundation")
+            .withPublicationDate(LocalDate.of(1942, 5, 1));
+
+    LOGGER.info("Stephen King Books:");
+    LOGGER.info(shining.toString());
+    LOGGER.info(darkTower.toString());
+
+    LOGGER.info("J.K. Rowling Books:");
+    LOGGER.info(chamberOfSecrets.toString());
+
+    LOGGER.info("Sci-fi Books:");
+    LOGGER.info(dune.toString());
+    LOGGER.info(foundation.toString());
+  }
+}
\ No newline at end of file
diff --git a/currying/src/main/java/com/iluwatar/currying/Book.java b/currying/src/main/java/com/iluwatar/currying/Book.java
new file mode 100644
index 000000000000..f9b7be05138a
--- /dev/null
+++ b/currying/src/main/java/com/iluwatar/currying/Book.java
@@ -0,0 +1,117 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * 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 com.iluwatar.currying;
+
+import java.time.LocalDate;
+import java.util.Objects;
+import java.util.function.Function;
+import lombok.AllArgsConstructor;
+
+/**
+ * Book class.
+ */
+@AllArgsConstructor
+public class Book {
+  private final Genre genre;
+  private final String author;
+  private final String title;
+  private final LocalDate publicationDate;
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    Book book = (Book) o;
+    return Objects.equals(author, book.author)
+            && Objects.equals(genre, book.genre)
+            && Objects.equals(title, book.title)
+            && Objects.equals(publicationDate, book.publicationDate);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(author, genre, title, publicationDate);
+  }
+
+  @Override
+  public String toString() {
+    return "Book{" + "genre=" + genre + ", author='" + author + '\''
+            + ", title='" + title + '\'' + ", publicationDate=" + publicationDate + '}';
+  }
+
+  /**
+   * Curried book builder/creator function.
+   */
+  static Function<Genre, Function<String, Function<String, Function<LocalDate, Book>>>> book_creator
+      = bookGenre
+          -> bookAuthor
+              -> bookTitle
+                  -> bookPublicationDate
+                      -> new Book(bookGenre, bookAuthor, bookTitle, bookPublicationDate);
+
+  /**
+   * Implements the builder pattern using functional interfaces to create a more readable book
+   * creator function. This function is equivalent to the BOOK_CREATOR function.
+   */
+  public static AddGenre builder() {
+    return genre
+        -> author
+            -> title
+                -> publicationDate
+                    -> new Book(genre, author, title, publicationDate);
+  }
+
+  /**
+   * Functional interface which adds the genre to a book.
+   */
+  public interface AddGenre {
+    Book.AddAuthor withGenre(Genre genre);
+  }
+
+  /**
+   * Functional interface which adds the author to a book.
+   */
+  public interface AddAuthor {
+    Book.AddTitle withAuthor(String author);
+  }
+
+  /**
+   * Functional interface which adds the title to a book.
+   */
+  public interface AddTitle {
+    Book.AddPublicationDate withTitle(String title);
+  }
+
+  /**
+   * Functional interface which adds the publication date to a book.
+   */
+  public interface AddPublicationDate {
+    Book withPublicationDate(LocalDate publicationDate);
+  }
+}
\ No newline at end of file
diff --git a/currying/src/main/java/com/iluwatar/currying/Genre.java b/currying/src/main/java/com/iluwatar/currying/Genre.java
new file mode 100644
index 000000000000..58e639f4ce3c
--- /dev/null
+++ b/currying/src/main/java/com/iluwatar/currying/Genre.java
@@ -0,0 +1,34 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * 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 com.iluwatar.currying;
+
+/**
+ * Enum representing different book genres.
+ */
+public enum Genre {
+  FANTASY,
+  HORROR,
+  SCIFI;
+}
diff --git a/pom.xml b/pom.xml
index b75a4551ff13..be6a09f4c9cc 100644
--- a/pom.xml
+++ b/pom.xml
@@ -200,6 +200,7 @@
     <module>composite-view</module>
     <module>metadata-mapping</module>
     <module>service-to-worker</module>
+    <module>currying</module>
     <module>serialized-entity</module>
     <module>identity-map</module>
     <module>component</module>


Test patch:
diff --git a/currying/src/test/java/com/iluwatar/currying/AppTest.java b/currying/src/test/java/com/iluwatar/currying/AppTest.java
new file mode 100644
index 000000000000..83fd99363e52
--- /dev/null
+++ b/currying/src/test/java/com/iluwatar/currying/AppTest.java
@@ -0,0 +1,39 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * 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 com.iluwatar.currying;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests that the App can be run without throwing any exceptions.
+ */
+class AppTest {
+  @Test
+  void executesWithoutExceptions() {
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+  }
+}
diff --git a/currying/src/test/java/com/iluwatar/currying/BookCurryingTest.java b/currying/src/test/java/com/iluwatar/currying/BookCurryingTest.java
new file mode 100644
index 000000000000..437941583618
--- /dev/null
+++ b/currying/src/test/java/com/iluwatar/currying/BookCurryingTest.java
@@ -0,0 +1,83 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * 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 com.iluwatar.currying;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDate;
+
+/**
+ * Unit tests for the Book class
+ */
+class BookCurryingTest {
+  private static Book expectedBook;
+
+  @BeforeAll
+  public static void initialiseBook() {
+    expectedBook = new Book(Genre.FANTASY,
+        "Dave",
+        "Into the Night",
+        LocalDate.of(2002, 4, 7));
+  }
+
+  /**
+   * Tests that the expected book can be created via curried functions
+   */
+  @Test
+  void createsExpectedBook() {
+    Book builderCurriedBook = Book.builder()
+        .withGenre(Genre.FANTASY)
+        .withAuthor("Dave")
+        .withTitle("Into the Night")
+        .withPublicationDate(LocalDate.of(2002, 4, 7));
+
+    Book funcCurriedBook = Book.book_creator
+            .apply(Genre.FANTASY)
+            .apply("Dave")
+            .apply("Into the Night")
+            .apply(LocalDate.of(2002, 4, 7));
+
+    assertEquals(expectedBook, builderCurriedBook);
+    assertEquals(expectedBook, funcCurriedBook);
+  }
+
+  /**
+   * Tests that an intermediate curried function can be used to create the expected book
+   */
+  @Test
+  void functionCreatesExpectedBook() {
+    Book.AddTitle daveFantasyBookFunc = Book.builder()
+      .withGenre(Genre.FANTASY)
+      .withAuthor("Dave");
+
+    Book curriedBook = daveFantasyBookFunc.withTitle("Into the Night")
+      .withPublicationDate(LocalDate.of(2002, 4, 7));
+
+    assertEquals(expectedBook, curriedBook);
+  }
+}