#flatMap

[not-toivo]

So, a single method call to flatMap is consistently slower than two method calls, to filter, and then map? The difference persists on smaller arrays (meaning, before the JIT compiler kicks in), see the last picture for an array of length 100. Not what I expected.

I guess, the lessons here are "don't be clever" and "avoid premature optimization".

[notarealwelder]

(Epistemic status: armchair theorizing)

Really, the hard part of monad explanations is not the idea of a monad. The heart of a monad fits into a sentence, and idiom of monadic code, into a paragraph! The question is rather of why: what's the point of monads? Why write code this way? How is all that useful, what problem does it solve, why that and not any other alternative?

I think this might be the question that often hangs unanswered in all the dissatisfied comments to monad tutorials; the question of motivation. And it is kind of tricky to answer, because (I claim) the principal use of monads and monadic code is to make it tenable to encode effects in type signatures. It's an important problem to solve, and it lets us write code with type-encoded side effects about as easily as ordinary imperative code with unchecked effects — a strict improvement, in principle — but...The solved problem is not directly related to the added capability; monads mitigate the inconvenience, not enhance capabilities directly. And the inconvenience is absent from the normal programming practice! Effects just happen, compiler sees them not, and composition is trivial. So the benefits are obvious from the assumption "all side effects are type-encoded" — >>= just collapses the boilerplate of manually composing consecutive effects, who wouldn't want that — but not otherwise, and it's kind of weird to answer "why monads?" with "actually the thing you want is type-encoded effects; monads are instrumental".

--but actually I wanted to sketch an in-order explanation; let's get to that.

---

Q: What is a monad?

A: Any type T<A> with a single parameter, which has a natural and sensible implementation of flatMap(T<A>, A -> T<B>) -> T<B>, is a monad. A: (Optionally, Monad can be an interface declared within the language that demands a flatMap from its implementations, but even absent that, types T<A> that have an accompanying flatMap deserve to be called monads.) A: ((Also, in fairness there's also the unit(A) -> T<A>, but it's slightly less important. ...and I don't have a reasonably intuitive motivation for it.)) A: Array<A> is a monad. Stream<A> is a monad. Future<A> is a monad. Option<A> is a monad. For a fixed Err, Result<A, Err> is a monad. Many more types are monads also, but: later. A: Values of type T<A> are typically called monadic values.

A: Secondly, monadic code is a code style / pattern in which several functions whose return type is T<_> are applied consecutively to each other's outputs with help of flatMap. So e.g. you can have all your business-logic functions return a Result<_, Err>, with Err encoding all the possible processing errors, and combine them uncomplicatedly: parseOptions().flatMap(loadThingsFromDisk).flatMap(parseThings).flatMap(resolveIDsViaDB).flatMap(performInstructedActions).......

Q: ........uh.....sure.....great? Why would I ever want to do that. Drop the flatMaps and that's a normal OOP processing pipeline, what's the point of all that...cruft. A: Two parts here. One, you can encode all kinds of side effects a function can have as {aptly named single-parameter types that implement flatMap} which appear in the function's return type. Pure functions except they produce some concatenatable side-output like logs: done, the Writer monad; pure functions except they are allowed to alter some delineated state: done, the State monad, pure functions except they're allowed read access to some unchangeable context—you get the idea. A: (Better yet, it's easy to modify most of those into a combinable form, so you can have functions that write a log, and touch a state, and might return an error, all those capabilities represented in the return type, and then compose them with the exact same flatMap.) A: Secondly, I claim that you really really want to encode side effects in return types. A: One good reason is readability. The Result<_, Err> type you learn once and use everywhere; to recognize it in new form again and again every time it's reimplemented is more effort and more errors. Res, Option, State all have standardized methods and contracts; after the tenth time you don't even need to think about their internal logic, it's just...obvious what will happen in a given chunk of code, or how to produce some particular effect you desire. A: And another, possibly more important: as long as side effects are type-encoded, you can delegate tracking them to the compiler. No more unexpected test or production breakages due to unexpected change in side-effects of some distant refactoring! No more unhandled null references! A new effect—or new variety-of-result, like Option or Result—won't compile until and unless you also fix all the consumers/use-locations of the altered function to cope with the new changes somehow.

A: With that in mind, monads are just all those type-encoded effects/capabilities where it's obvious how consecutive applications of the effect / invocations of the capability should be combined; that is, where the combining logic is enshrined in that type's flatMap. Their main use is to work with type-encoded effects comparatively painlessly, letting us have considerable benefits of such encoding without the otherwise-noticeable cost of composing effects manually.

<Q has further critique, but A is out of exposition.>

[ssblur]

ifPresent() over flatMap(stream)? using streams in a mixin body??? sorry blur pal i think we actually hafta kill you for this one

(:

[newpronounswhodis]

you like haskell?

explain what a monad is!

a monad is a type with a flatmap operation and I’m tired of people overcomplicating it

consider some type M which is generic over T. in rust that is expressed as “struct M<T>”, or in haskell as “data M a = …”. If there is a function with the signature “M a -> (a -> M b) -> M b”, then it is a Monad. Simple as

[forever-stuck-on-java-8]

This is just Java Slander. And skill issue.

First of all, steam() isn't necessary for forEach() you could simplify it to: list.forEach(list2::add)

However this entire thing can be simplified to list2.addAll(list).

If you need the result in a new list, their are multiple ways to do so:

Normal way: List<> newList = new ArrayList<>(list2); newList.addAll(list);

Using Stream: List<> newList = Stream.concat(list.stream(), list2.stream()).collect(Collectors.toList());

Using Stream.of() (which can do more than 2): List<> newList = Stream.of(list, list2, list3) .flatMap(Collection::stream) .collect(Collectors.toList());

Using Apache Commons: List<> newList = ListUtils.union(list1, list2);

i fucking hate writing java dude what do you mean list.stream().forEach(list2::add)??!

syntax written by clowns

[souhaillaghchimdev]

Kotlin: 100 Simple Codes

Kotlin: 100 Simple Codes

beginner-friendly collection of easy-to-understand Kotlin examples.

Each code snippet is designed to help you learn programming concepts step by step, from basic syntax to simple projects. Perfect for students, self-learners, and anyone who wants to practice Kotlin in a fun and practical way.

Codes:

1. Hello World

2. Variables and Constants

3. If-Else Statement

4. When Statement (Switch)

5. For Loop

6. While Loop

7. Functions

8. Return Value from Function

9. Array Example

10. List Example

===

11. Mutable List

12. Map Example

13. Mutable Map

14. Class Example

15. Constructor with Default Value

16. Nullable Variable

17. Safe Call Operator

18. Elvis Operator

19. Data Class

20. Loop with Index

===

21. Lambda Function

22. Higher-Order Function

23. Filter a List

24. Map a List

25. String Interpolation

26. String Templates with Expressions

27. Read-Only vs Mutable List

28. Check Element in List

29. Exception Handling

30. Null Check with let

===

31. For Loop with Step

32. For Loop in Reverse

33. Break in Loop

34. Continue in Loop

35. Check String Empty or Not

36. Compare Two Numbers

37. Array Access by Index

38. Loop Through Map

39. Default Parameters in Function

40. Named Arguments

===

41. Range Check

42. Function Returning Unit

43. Multiple Return Statements

44. Chained Method Calls

45. Function Inside Function

46. Function Expression Syntax

47. Array Size

48. String to Int Conversion

49. Safe String to Int Conversion

50. Repeat Block

===

51. Sealed Class

52. Object Expression (Anonymous Object)

53. Singleton using Object Keyword

54. Extension Function

55. Enum Class

56. Use Enum in When Statement

57. Type Alias

58. Destructuring Declarations

59. Companion Object

60. Simple Interface Implementation

===

61. Abstract Class

62. Lateinit Variable

63. Initialization Block

64. Secondary Constructor

65. Nested Class

66. Inner Class

67. Generic Function

68. Generic Class

69. Custom Getter

70. Custom Setter

===

71. String Equality

72. Loop with Range Until

73. Using Pair

74. Triple Example

75. Check Type with is

76. Smart Cast

77. Type Casting with as

78. Safe Casting with as?

79. Loop Through Characters of String

80. Sum of List

===

81. Min and Max of List

82. Sort List

83. Reverse List

84. Count Items in List

85. All / Any Conditions

86. Check if List is Empty

87. Join List to String

88. Take and Drop

89. Zipping Lists

90. Unzipping Pairs

===

91. Chunked List

92. Windowed List

93. Flatten List

94. FlatMap

95. Remove Duplicates

96. Group By

97. Associate By

98. Measure Execution Time

99. Repeat with Index

100. Create Range and Convert to List

===

[eccentric-nucleus]

```parseExpr("$foobar + $baz * 2 * %quux").flatMap (expr => evaluateExpr ({local: {quux: 12}, global: {foobar: 5, baz: 10}}, expr))

Object { right: 1, val: 245 }```

well that was easy :toot:

[javainspires]

Java 8 FlatMap Example Java Inspires

[javatute673]

Java Stream flatMap()

[notarealwelder]

A monad is any single-parameter type that has a natural and sensible flatMap, what's the problem

maths student naïvely asks for the definition of a tensor, causes world war 3, more on this story at 7

[proeduorganization]

Apache Spark flatMap transformation

Apache Spark flatMap transformation

Apache Spark flatMap transformation Apache Spark In our previous post, we talked about the Map transformation in Spark. In this post we will learn the flatMap transformation. As per Apache Spark documentation, flatMap(func) is similar to map, but each input item can be mapped to 0 or more output items That means the func should return a scala.collection.Seq rather than a single item. Let’s…

[magicalalehouse]

Made a top view of the proposed scene, with a half buried hedron in the middle nad a broken on the side. squares represents cabins and circle represent trees. Circle with a cross represent more lifeless tree, purhaps burned and snow covered? The sky should also contain some hedrons floating in the distance. Hedrons should be futuristic but with exposed components representing damage perhaps? Or can go for a more steampunk vibe with pistons outside? Cabins need to be primitive and maybe even collapsed cabins. the whole scene need to be covered in snow. Have not yet decided if human figures will be included. Could add some smoke indicating camp fire.

[hunteroil456]

Crusader Kings 3 Lord Of The Rings

Crusader Kings in Middle-earth. Announcing LotR: Realms in Exile for CK3. We have a map, and a team. And are looking for people to share in our adventures.(reddit.com)

Crusader Kings 3 Lord Of The Rings Mods

Crusader Kings 3 Lord Of The Rings Movies

Crusader Kings II is a sequel to the historical Real-Time Strategy game Crusader Kings also by Paradox Interactive.Playing similarly to the first game, with the player controlling the leader of a dynasty rather than acting as an abstract Non-Entity General, this iteration added several more features like character ambitions, an expanded plotting and intrigue mechanic, a revamp of the holy. An expansive medieval grand-strategy game of war, intrigue, and custom character design – of course there’s a Lord of the Rings mod for Crusader Kings 3. The premise is simple enough: take the vanilla game’s core gameplay and plonk it into the realm of Middle-earth, complete with a lovingly-designed map, character portraits of your.

Welcome to another Mod Monday where we cover the Best Ck3 mods of the week or weeks? Sub here: Mondays: Mods. Welcome to Amazon UK’s PC & Video Games Shop. Browse the latest consoles and games; includes PS4, Xbox One, Nintendo Wii U, PC Games & more.

submitted by Barad-Dûr

Crusader Kings in Middle-earth. Announcing LotR: Realms in Exile for CK3. We have a map, and a team. And are looking for people to share in our adventures.

Crusader Kings 3 Lord Of The Rings Mods

7,509 points•368 comments•submitted by to r/CrusaderKings

Caption: The realms of Middle-earth. This is for the first release, future releases will include Gondor, Mordor, Erebor, Rhovanion, Mirkwood and more.

Crusader Kings 3 Lord Of The Rings Movies

Caption: The hand-drawn flatmap. It's much bigger than this...

[programmerhumour]

When you forget to use flatMap

[lovecreat12345]

FlatMap In Angular

FlatMap In Angular

This Article is about FlatMap In Angular. Let’s say we wanted to implement an AJAX search feature in which every keypress in a text field will automatically perform a search and update the page with the results. How would this look? Well we would have an Observablesubscribed to events coming from an input field, and on every change of input we want to perform some HTTP…