# Monads-in-Java | An encoding of monads in the Java Language | Functional Programming library

## kandi X-RAY | Monads-in-Java Summary

## kandi X-RAY | Monads-in-Java Summary

Simple encoding of monads in the java language. In order to make class M a monad, implement Monad. Then annotate M with @InjectWith, and an appropriate Return implementation. The return and >> methods are called inject and chainIgnore and in the Monads utility class. See main/monad4j.examples.maybe package for a Maybe type as a monad See test/monad4j.examples.maybe.TestMaybeIsAMonad for tests for the 3 monadic laws.

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### Top functions reviewed by kandi - BETA

- Lift a function to a monad
- Instantiates a Monad with a class
- Inject value
- Construct a Maybe value
- Creates a new empty Maybe
- Returns a no value
- Checks for equality
- Generate a hash code for this instance
- Chain a monad ignoring void
- Combine a monad
- Do a case
- Implements the visitor to handle case cases
- Gets the hashCode of this class

## Monads-in-Java Key Features

## Monads-in-Java Examples and Code Snippets

## Community Discussions

Trending Discussions on Functional Programming

QUESTION

I have been trying to learn about functional programming, but I still struggle with thinking like a functional programmer. One such hangup is how one would implement index-heavy operations which rely strongly on loops/order-of-execution.

For example, consider the following Java code:

...ANSWER

Answered 2022-Mar-07 at 21:17This is not an index-heavy operation, in fact you can do this with a one-liner with ** scanl1 :: (a -> a -> a) -> [a] -> [a]**:

QUESTION

I want to write a function that checks if the first list is longer than the second list and one of them can be infinite. However I can't find a working solution.

...ANSWER

Answered 2022-Mar-22 at 20:54Plain old natural numbers will not do the trick, because you can't calculate the natural number length of an infinite list in finite time. However, *lazy* natural numbers can do it.

QUESTION

Haskell provides a convenient function `forever`

that repeats a monadic effect indefinitely. It can be defined as follows:

ANSWER

Answered 2022-Feb-05 at 20:34The execution engine starts off with a pointer to your loop, and lazily expands it as it needs to find out what `IO`

action to execute next. With your definition of `forever`

, here's what a few iterations of the loop like like in terms of "objects stored in memory":

QUESTION

I was solving a recursive problem in haskell, although I could get the solution I would like to cache outputs of sub problems since has over lapping sub-problem property.

The question is, given a grid of dimension `n*m`

, and an integer `k`

, how many ways are there to reach the gird (n, m) from (1, 1) with not more than k change of direction?

Here is the code without of memoization

...ANSWER

Answered 2021-Dec-16 at 16:23In Haskell these kinds of things aren't the most trivial ones, indeed. You would really like to have some in-place mutations going on to save up on memory and time, so I don't see any better way than equipping the frightening `ST`

monad.

This could be done over various data structures, arrays, vectors, repa tensors. I chose `HashTable`

from hashtables because it is the simplest to use and is performant enough to make sense in my example.

First of all, introduction:

QUESTION

I have a function in Haskell that is defined as follows:

...ANSWER

Answered 2021-Nov-30 at 09:42Haskell values have types. Each value has a type. One type. It can't be two different types at the same time.

Thus, since `x`

is returned as the result of `if`

's consequent, the type of the whole `if ... then ... else ...`

expression is the same as `x`

's type.

An `if`

expression has a type. Thus both its consequent and alternative expression must have that same type, since either of them can be returned, depending on the value of the test. Thus both must have the same type.

Since `x`

is also used in the test, it must be `Bool`

. Then so must be `y`

.

QUESTION

What is the syntax for a vector (array) of functions in APL?

I have tried the following but these are interpreted as a 3-train and a 2-train, respectively:

...ANSWER

Answered 2021-Nov-28 at 23:26Dyalog APL does not officially support function arrays, you can awkwardly emulate them by creating an array of namespaces with identically named functions.

QUESTION

In F# if I write

...ANSWER

Answered 2021-Nov-17 at 01:24To expand on the answer given in the comments, the first `p`

is an immutable value, while the second `p`

is a function. If you refer to an immutable value multiple times, then (obviously) its value doesn't change over time. But if you invoke a function multiple times, it executes each time, *even if the arguments are the same each time*.

Note that this is true even for pure functional languages, such as Haskell. If you want to avoid this execution cost, there's a specific technique called memoization that can be used to return cached results when the same inputs occur again. However, memoization has its own costs, and I'm not aware of any mainstream functional language that automatically memoizes all function calls.

QUESTION

I'm working trough the book Haskell in depth and I noticed following code example:

...ANSWER

Answered 2021-Nov-03 at 06:39`Reader`

's type parameters aren't in the right order for that to be `contramap`

for it. A `Contravariant`

functor always needs to be contravariant in its last type parameter, but `Reader`

is contravariant in its first type parameter. But you can do this:

QUESTION

I am experimenting with clojure's lazy sequences. In order to see when the evaluation of an item would occur, I created a function called square that prints the result before returning it. I then apply this function to a vector using map.

...ANSWER

Answered 2021-Oct-20 at 15:49Laziness isn't all-or-nothing, but some implementations of seq operate on 'chunks' of the input sequence (see here for an explanation). This is the case for vector which you can test for with `chunked-seq?`

:

QUESTION

Haskell lists are constructed by a sequence of calls to `cons`

, after desugaring syntax:

ANSWER

Answered 2021-Aug-30 at 04:46Lists in Haskell are special **in syntax**, but not fundamentally.

Fundamentally, Haskell list is defined like this:

Community Discussions, Code Snippets contain sources that include Stack Exchange Network

## Vulnerabilities

No vulnerabilities reported

## Install Monads-in-Java

You can use Monads-in-Java like any standard Java library. Please include the the jar files in your classpath. You can also use any IDE and you can run and debug the Monads-in-Java component as you would do with any other Java program. Best practice is to use a build tool that supports dependency management such as Maven or Gradle. For Maven installation, please refer maven.apache.org. For Gradle installation, please refer gradle.org .

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