LambdaUtil

LambdaUtil is a swiss-knife-like utility tool to kickstart the lambda style functional programming in Java. Lambda-styled programaming syntaxes are partly supported by java since version 8.0 was released. However, the monads for objects and collections, supplied by the factory, are not complete. Most importantly, the functional interfaces lack error handling. Finally, it becomes impossible to write clean chain-like code by using the standard java. LambdaUtil is an extremely lightweight and barebone collections of monads and functional interfaces. Still, it allows developers to transform data by performing a sequence of operations in a clean chain-like code block for almost every programming need. With these blocks of chain like code, the entire java program can be written without using many standard java keywords. For example, no messy try-catch block is necessary, as the exceptions are handled by the monad automatically. Similarly, the if-else-endif or the switch-case block also becomes unnecessary, as a combination of predicate and functions. In short, this tool may write your entire java program without using curly braces. In the end, this style of programming helps in avoiding embarrassing crashes due to a missed error handling, unwanted mutation of collections, and data leaks.

Availibility

• Maven: Add the following block in .pom file in your project.

<dependency>
  <groupId>edu.ohiou.mfgresearch</groupId>
  <artifactId>LambdaUtil</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
</dependency>

• Compile from source: Build the project by Maven using the following commands (Maven required)

How to use

Monads:

LambdaUtil provides two monads, which are called Uni and Omni, to wrap around a single java object and collection of java object(s), respectively. Primitive type classes are also supported but not primitive types, i.e Integer is supported but not int.

Uni

Uni wraps around any java object and provides a list of functors to transform the object in various ways. Three monadic properties of Uni are:

• identity:
• fMap:
• reverse:

Constructor

Any object can be wrapped in Uni by passing either the object or a supplier for that object by using the static method of.

Uni.of("Hello, world!");
Uni.of(new String("Hello, world!"));
Uni.of(()->"Hello, world!");
Uni.of(()->new String("Hello, world!"));

Transformation

• map: map applies an instance of Func interface, which receives the object, already wrapped in the Uni, and returns an object of same or some other type. This object is returned by map as an Uni.

  Uni.of("Hello, world!").map(t->5.0); 
  

• fMap: fMap applies an instance of Func interface, which receives the object, already wrapped in the Uni, and returns a collection, wrapped in Omni. This Omni-typed object is returned by fMap.

  Uni.of("Hello, world!").fMap(s->Omni.of(s.split(",")));
  

• fMap2Stream: fMap2Stream applies an instance of Func interface, which receives the object, already wrapped in the Uni, and returns a collection of Uni, wrapped in java.util.stream.Stream. This stream of Uni is returned by fMap2Stream. This is a utility method, which breaks the chain-like code but helps in switching to standard Stream implementation from Java.

  Uni.of("Hello, world!").fMap(s->Omni.of(s.split(",")));
  

• set: set applies an instance of Cons (consumer) to the object and returns the same object, wrapped in Uni. This is a utility method, which does not change the object at all. However, the object may be decorated by setting its properties. This functor may also be used to perform additional tasks, which may require the object but do not necessarily change it.

  Uni.of(new File()).fMap(s->Omni.of(s.split(",")));
  

Selection

• filter: filter applies an instance of Pred interface and returns the same Uni object if the supplied predicate succeeds. It returns a Failure object if the predicates fails.

  Uni.of("Hello, world!")
     .filter(s->s.contains("Hello"))  //returns same Uni
     .filter(s->s.contains("Hola"));  //returns failure object 
  

• select: select applies an instance of Pred (predicate) and then passes the object to an instance of Cons (consumer) if the predicate succeeds. It returns the same Uni object irreespective of the given predicate succeeding or failing but does not invoke the the given consumer, if the predicate fails.

  Uni.of(5)
  .select(i->i%2==0, i->System.out.println(i+" is even. "))
  .select(i->i%2!=0, i->System.out.println(i+" is odd. "));
  (prints "5 is odd.")   
  

• selectMap: selectMap applies an instance of Pred (predicate) interface and then passes the object to an instance of Func (function) if the supplied predicate succeeds. It returns the object, which is returned by the function, after wrapping it in Uni. It returns the same Uni object and does not pass the object to the given function if the predicate fails.

  Uni.of(5)
     .select(i->i%2!=0, i->i+1);
  (returns Uni<6>)   
  

Error handling

• onFailure: onFailure accepts an instance of Cons and passes the exception object to it if occurs in the preceding invocations of functors. The consumer is never applied if no exception occurs.

  Uni.of(5)
     .map(i->i/0)
     .onFailure(e->System.out.println("ArithmeticException has occurred!"));
  

• onSucess: onSuccess accepts an instance of Cons and passes the object to it if no exception occurs in the preceding invocations of functors. The consumer is never applied if any exception occurs.

  Uni.of(5)
     .map(i->i/n)
     .onFailure(e->System.out.println("ArithmeticException has occurred!"))
     .onSuccess(i->System.out.println("Division is performed successfully"));
  (returns Uni<6>)   
  

Getters

• get: get returns the object, which is wrapped in the Uni. This method breaks the chain and should be used to assign the result of the operations in a variable at the end of the chain.

  Double factorial5 = Uni.of(5)
  		    .map(i->Math.sqrt(5))
  		    .get()
  

Omni

Omni wraps around a java collection of any type and provides a list of functors to transform the collection in various ways. Three monadic properties of Omni are:

• identity:
• fMap:
• reverse:

Constructor

A java list or an array can be wrapped in Omni by passing either the object or a supplier for that object by using the static method of.

Omni.of("Hello", ", ", "world", "!"); //from a list of items

//from a list of items
Omni.of(new "Hello", ", ", "world", "!");

//from a list
List<Integer> numbers = new LinkedList<Integer>();
numbers.add(1);
numbers.add(2);
numbers.add(3);
Omni.of(numbers);

Omni.of(IntStream.range(1, 10).toArray()); //from a java stream object

Transformation

• map: map applies an instance of Func (function), which returns object of any type, to every item of the collection. Every item in the collection is replaced by the object returned by the function. One or more objects may be replaced by a Failure object if the function fails for that object as argument.

  Omni.of(1, 2, 3, 4).map(i->i**2)
  

• fMap: fMap applies an instance of Func (function), which returns Omni of any type. to every item of the collection. Every item in the collection is replaced by one or more objects in the Omni returned by the function. In other words the all the collections, returned by applying the given function to every item of the original collection in the Omni, are flattened in the Omni, returned by this functor. One or more objects may be replaced by a Failure object if the function fails for that object as argument.

  Uni.of("Hello, world!").fMap(s->Omni.of(s.split(",")));
  

• fMap2Stream: fMap2Stream applies an instance of Func interface, which receives the object, already wrapped in the Uni, and returns a collection of Uni, wrapped in java.util.stream.Stream. This stream of Uni is returned by fMap2Stream. This is a utility method, which breaks the chain-like code but helps in switching to standard Stream implementation from Java.

  Uni.of("Hello, world!").fMap(s->Omni.of(s.split(",")));
  

• set: set applies an instance of Cons (consumer) to the object and returns the same object, wrapped in Uni. This is a utility method, which does not change the object at all. However, the object may be decorated by setting its properties. This functor may also be used to perform additional tasks, which may require the object but do not necessarily change it.

  Uni.of(new File()).fMap(s->Omni.of(s.split(",")));
  

Selection

• filter: filter applies an instance of Pred interface and returns the same Uni object if the supplied predicate succeeds. It returns a Failure object if the predicates fails.

  Uni.of("Hello, world!")
     .filter(s->s.contains("Hello"))  //returns same Uni
     .filter(s->s.contains("Hola"));  //returns failure object 
  

• select: select applies an instance of Pred (predicate) and then passes the object to an instance of Cons (consumer) if the predicate succeeds. It returns the same Uni object irreespective of the given predicate succeeding or failing but does not invoke the the given consumer, if the predicate fails.

  Uni.of(5)
  .select(i->i%2==0, i->System.out.println(i+" is even. "))
  .select(i->i%2!=0, i->System.out.println(i+" is odd. "));
  (prints "5 is odd.")   
  

• selectMap: selectMap applies an instance of Pred (predicate) interface and then passes the object to an instance of Func (function) if the supplied predicate succeeds. It returns the object, which is returned by the function, after wrapping it in Uni. It returns the same Uni object and does not pass the object to the given function if the predicate fails.

  Uni.of(5)
     .select(i->i%2!=0, i->i+1);
  (returns Uni<6>)   
  

Error handling

• onFailure: onFailure accepts an instance of Cons and passes the exception object to it if occurs in the preceding invocations of functors. The consumer is never applied if no exception occurs.

  Uni.of(5)
     .map(i->i/0)
     .onFailure(e->System.out.println("ArithmeticException has occurred!"));
  

• onSucess: onSuccess accepts an instance of Cons and passes the object to it if no exception occurs in the preceding invocations of functors. The consumer is never applied if any exception occurs.

  Uni.of(5)
     .map(i->i/n)
     .onFailure(e->System.out.println("ArithmeticException has occurred!"))
     .onSuccess(i->System.out.println("Division is performed successfully"));
  (returns Uni<6>)   
  

Getters

• get: get returns the object, which is wrapped in the Uni. This method breaks the chain and should be used to assign the result of the operations in a variable at the end of the chain.

  Double factorial5 = Uni.of(5)
  		    .map(i->Math.sqrt(5))
  		    .get()