fpdart

v1.2.0 - 29 October 2025

• Added toTaskOptionFlat, toTaskEitherFlat, fromTaskFlatten to TaskOption and TaskEither
• Added new iterable extension functions singleOption, elementAtOption, singleWhereOption, lastWhereOption
• Minor internal improvements
• Status update for fpdart v2 (full discussion here)

v1.1.1 - 7 November 2024

• Fixed broken documentation links

v1.1.0 - 13 August 2023

• Improved performance of some iterable based functions in Iterable and Map extension (thanks to lrhn 🎉)

• Added lookupEq and dropRight on Iterable extension

[].lookupEq(Eq.eqInt, 5) // None()
[1, 2, 3, 4].lookupEq(Eq.eqInt, 5) // None()
[1, 2, 3, 4].lookupEq(Eq.eqInt, 3) // Some(3)
[1, 6, 4, 3, 2].lookupEq(Eq.by((n) => n % 3, Eq.eqInt), 0) // Some(6)

[1, 2].dropRight(3) // []
[1, 2, 3, 4].dropRight(1) // [1, 2, 3]

• Added lookupKeyEq on Map extension

<String, int>{'a': 1, 'b': 2, 'c': 3, 'd': 4}.lookupKeyEq(Eq.eqString, 'b'); // Some('b')
<String, int>{'a': 1, 'b': 2, 'c': 3, 'd': 4}.lookupKeyEq(Eq.eqString, 'e'); // None()

v1.0.0 - 27 May 2023

• Minimum environment dart sdk to 3.0.0 ⚠️ (Dart 3️⃣)

environment:
  sdk: ">=3.0.0 <4.0.0"

• Added new ReaderTaskEither type
  • ReaderTaskEither models a complete program using Reader for dependency injection, Task to perform asynchronous computation, and Either to handle errors 🎯
• Added new ReaderTask type
• Either as sealed class (Dart 3️⃣)
  • You can now use exhaustive pattern matching (Left or Right)

/// Pattern matching
final match = right.match(
  (l) => print('Left($l)'),
  (r) => print('Right($r)'),
);

/// or use Dart's pattern matching as well 🤝
final dartMatch = switch (right) {
  Left(value: final l) => 'Left($l)',
  Right(value: final r) => 'Right($r)',
};

• Option as sealed class (Dart 3️⃣)
  • You can now use exhaustive pattern matching (None or Some)

/// Pattern matching
final match = option.match(
  () => print('None'),
  (a) => print('Some($a)'),
);

/// or use Dart's pattern matching as well 🤝
final dartMatch = switch (option) {
  None() => 'None',
  Some(value: final a) => 'Some($a)',
};

• Types marked as final (no extends nor implements) (Dart 3️⃣)
  • Unit
  • Reader
  • State
  • StateAsync
  • IO
  • IORef
  • IOOption
  • IOEither
  • Task
  • TaskOption
  • TaskEither
  • ReaderTask
  • ReaderTaskEither
• Removed Tuple2, use Dart 3 Records instead (Tuple2(a, b) becomes simply (a, b) 🎯) ⚠️ (Dart 3️⃣)
  • Updated all internal APIs to use records instead of Tuple2
• Major refactoring of Iterable and List extension methods
  • Improved performance
  • Correct return types (Iterable and List) (#65)
  • Added the following methods
    • prependAll (Iterable)
    • intersperse (Iterable)
    • difference (Iterable)
    • filterWithIndex (Iterable)
  • Fixed the following methods ⚠️
    • takeWhileRight: Resulting List now in reversed order as expected
    • dropWhileRight: Resulting List now in reversed order as expected
  • Updated the following methods ⚠️
    • foldRight, foldRightWithIndex (List): Changed parameter order in combine function
    • zipWith (Iterable): Changed parameters definition, no more curried
  • Renamed the following methods ⚠️
    • plus → concat (Iterable)
    • concat → flatten (on Iterable<Iterable<T>>)
  • Removed the following methods ⚠️
    • concatMap (use flatMap instead)
    • bind (use flatMap instead)
    • bindWithIndex (use flatMapWithIndex instead)
    • concatMapWithIndex (use flatMapWithIndex instead)
• Refactoring of Map extension methods
  • Improved performance
  • Added the following methods
    • lookupEq
    • lookupWithKeyEq
  • Removed the following methods ⚠️
    • member (use containsKey instead)
    • elem (use containsValue instead)
    • toIterable (use toSortedList instead)
  • Updated the following methods ⚠️
    • toIterable renamed to toSortedList (return a List instead of Iterable)
    • modifyAt changed parameter order and no more curried
    • modifyAtIfPresent changed parameter order and no more curried
    • updateAt no more curried
    • updateAtIfPresent no more curried
    • deleteAt no more curried
    • upsertAt no more curried
    • pop no more curried
    • foldLeft no more curried
    • foldLeftWithKey no more curried
    • foldLeftWithIndex no more curried
    • foldLeftWithKeyAndIndex no more curried
    • foldRight no more curried
    • foldRightWithKey no more curried
    • foldRightWithIndex no more curried
    • foldRightWithKeyAndIndex no more curried
    • union no more curried
    • intersection no more curried
    • isSubmap no more curried
    • collect no more curried
    • difference no more curried
• Added conversions helpers from String to num, int, double, and bool using Option and Either (both as extension methods on String and as functions) (#80)
  • toNumOption
  • toIntOption
  • toDoubleOption
  • toBoolOption
  • toNumEither
  • toIntEither
  • toDoubleEither
  • toBoolEither

/// As extension on [String]
final result = "10".toNumOption; /// `Some(10)`
final result = "10.5".toNumOption; /// `Some(10.5)`
final result = "0xFF".toIntOption; /// `Some(255)`
final result = "10.5".toDoubleOption; /// `Some(10.5)`
final result = "NO".toBoolEither(() => "left"); /// `Left("left")`

/// As functions
final result = toNumOption("10"); /// `Some(10)`
final result = toNumOption("10.5"); /// `Some(10.5)`
final result = toIntOption("0xFF"); /// `Some(255)`
final result = toDoubleOption("10.5"); /// `Some(10.5)`
final result = toBoolEither("NO", () => "left"); /// `Left("left")`

• Changed dateNow, now, random, and randomBool to getter functions

/// Before
Option<T> getRandomOption<T>(T value) => randomBool()
    .map((isValid) => isValid ? some(value) : none<T>())
    .run();

/// Now
Option<T> getRandomOption<T>(T value) => randomBool
    .map((isValid) => isValid ? some(value) : none<T>())
    .run();

• Removed Predicate class and added extension methods in its place ⚠️

bool isEven(int n) => n % 2 == 0;
bool isDivisibleBy3(int n) => n % 3 == 0;

final isOdd = isEven.negate;
final isEvenAndDivisibleBy3 = isEven.and(isDivisibleBy3);
final isEvenOrDivisibleBy3 = isEven.or(isDivisibleBy3);
final isStringWithEvenLength = isEven.contramap<String>((n) => n.length);

• Updated curry / uncarry extensions ⚠️
  • Renamed curry to curryAll for functions with 3, 4, 5 parameters
  • Changed definition of curry to curry only the first parameter
  • Changed uncurry and curry extension to getter function
  • Removed curry and uncurry as functions (use extension method instead)
  • Added curryLast (curry last parameter)

int Function(int) subtractCurried(int n1) => (n2) => n1 - n2;

/// Before
subtractCurried.uncurry()(10, 5);

final addFunction = (int a, int b) => a + b;
final add = curry2(addFunction);

[1, 2, 3].map(add(1));  // returns [2, 3, 4]

/// New
subtractCurried.uncurry(10, 5);

final addFunction = (int a, int b) => a + b;
final add = addFunction.curry;

[1, 2, 3].map(add(1)); // returns [2, 3, 4]
[1, 2, 3].map(addFunction.curry(1)); // returns [2, 3, 4]

• Changed Eq static constructors to methods
  • or
  • and
• Added xor method to Eq
• Moved DateTime instances of Eq as Eq static members

/// Before
final eq = dateEqYear; // Global

/// Now
final eq = Eq.dateEqYear;

• Added Eq instances for num, int, double, String, and bool

[1, 2, 3].difference(Eq.eqInt, [2, 3, 4]); /// `[1]`

• Added new method to Eq
  • contramap

class Parent {
  final int value1;
  final double value2;
  const Parent(this.value1, this.value2);
}

/// Equality for values of type [Parent] based on their `value1` ([int]).
final eqParentInt = Eq.eqInt.contramap<Parent>(
  (p) => p.value1,
);

/// Equality for of type [Parent] based on their `value2` ([double]).
final eqParentDouble = Eq.eqDouble.contramap<Parent>(
  (p) => p.value2,
);

• Changed reverse in Order from static constructor to getter method

/// Before
final reversed = Order.reverse(instance);

/// Now
final reversed = instance.reverse;

• Moved DateTime instances of Order as Order static members
• Added Order instances for num, int, double
• Added new methods to Order
  • between
  • clamp
  • contramap

class Parent {
  final int value1;
  final double value2;
  const Parent(this.value1, this.value2);
}

/// Order values of type [Parent] based on their `value1` ([int]).
final orderParentInt = Order.orderInt.contramap<Parent>(
  (p) => p.value1,
);

/// Order values of type [Parent] based on their `value2` ([double]).
final orderParentDouble = Order.orderDouble.contramap<Parent>(
  (p) => p.value2,
);

• Removed bool extension (match and fold), use the ternary operator or pattern matching instead ⚠️

final boolValue = Random().nextBool();

/// Before
final result = boolValue.match<int>(() => -1, () => 1);
final result = boolValue.fold<int>(() => -1, () => 1);

/// Now
final result = boolValue ? 1 : -1;
final result = switch (boolValue) { true => 1, false => -1 };

• Removed global id and idFuture, use identity and identityFuture instead ⚠️
• Removed global idFirst and idSecond functions ⚠️
• Removed Compose class and extension methods ⚠️
• Removed Magma typedef ⚠️
• Removed extension methods on nullable types (toOption, toEither, toTaskOption, toIOEither, toTaskEither, toTaskEitherAsync) ⚠️
• Organized all extensions inside internal extension folder
• Updated README
  • Getting started with fpdart complete guide
  • Full history of fpdart and functional programming in dart

---

v0.6.0 - 6 May 2023

• Do notation #97 (Special thanks to @tim-smart 🎉)
  • All the main types now have a Do() constructor used to initialize a Do notation chain
  • Updated examples to use Do notation (new recommended API 🎯)

/// Without the Do notation
String goShopping() => goToShoppingCenter()
    .alt(goToLocalMarket)
    .flatMap(
      (market) => market.buyBanana().flatMap(
            (banana) => market.buyApple().flatMap(
                  (apple) => market.buyPear().flatMap(
                        (pear) => Option.of('Shopping: $banana, $apple, $pear'),
                      ),
                ),
          ),
    )
    .getOrElse(
      () => 'I did not find 🍌 or 🍎 or 🍐, so I did not buy anything 🤷‍♂️',
    );

/// Using the Do notation
String goShoppingDo() => Option.Do(
      (_) {
        final market = _(goToShoppingCenter().alt(goToLocalMarket));
        final amount = _(market.buyAmount());

        final banana = _(market.buyBanana());
        final apple = _(market.buyApple());
        final pear = _(market.buyPear());

        return 'Shopping: $banana, $apple, $pear';
      },
    ).getOrElse(
      () => 'I did not find 🍌 or 🍎 or 🍐, so I did not buy anything 🤷‍♂️',
    );

• Added new IOOption type
• Added conversion methods from and to all classes (IO, IOOption, IOEither, Task, TaskOption, TaskEither)
  • Removed toTask in IOEither (use toTaskEither instead) ⚠️
• Improved performance of fpdart's sortBy list extension #101 (thanks to @hbock-42 🎉)
• Updated pokeapi_functional example to Riverpod v2 #99 (thanks to @utamori 🎉)
• Updated repository folder structure #105

v0.5.0 - 4 March 2023

• Updates to Option type #92 [⚠️ BREAKING CHANGE]
  • Added const factory constructor for None (fixes #95)
  • Removed Alt and Foldable type classes, the following methods are not available anymore
    • foldLeft
    • foldRight
    • foldMap
    • foldRightWithIndex
    • foldLeftWithIndex
    • length
    • any
    • all
    • concatenate
    • plus
    • prepend
    • append
• Updated examples and fixed lint warnings #93 (thanks to tim-smart 🎉)

v0.4.1 - 25 February 2023

• New methods for Option type (thanks to tim-smart 🎉)
  • flatMapNullable
  • flatMapThrowable

final option = Option.of(10);

option.flatMapNullable((a) => a + 1); /// 👈 `Some(11)`
option.flatMapThrowable((a) => a + 1); /// 👈 `Some(11)`

option.flatMapNullable<int>((a) => null); /// 👈 `None()`
option.flatMapThrowable<int>((a) => throw "fail"); /// 👈 `None()`

• Improved support fromJson for Option type (thanks [again] to tim-smart 🎉)
  • Allow for decoding of non-primitive types (with custom fromJson constructors)

/// `fromJson` on `DateTime` with `Option` type
final now = DateTime.now();
Option<DateTime>.fromJson(now.toIso8601String(), (a) => DateTime.parse(a as String)); /// 👈 `Some(now)`

Option<DateTime>.fromJson("fail", (a) => DateTime.parse(a as String)); /// 👈 `None()`

• New extension methods for Map (thanks [once again] to tim-smart 🎉)
  • extract
  • extractMap

final map = <String, dynamic>{'a': 1, 'b': 2, 'c': 3, 'd': 4};
map.extract<int>('b'); /// 👈 `Some(2)`
map.extract<String>('b'); /// 👈 `None()`, not of type `String` ⚠️

final map = <String, dynamic>{'a': 1};
map.extractMap('a'); /// 👈 `None()`, not a `Map`

final map = <String, dynamic>{'a': {'b': 2} };
map.extractMap('a'); /// 👈 `Some({'b': 2})`

• Option.of and Option.none factories const (thanks to f-person 🎉)

Note: People who have the prefer_const_constructors lint enabled will notice a warning to use const 🤝

• New managing_imports example (thanks to RandalSchwartz 🎉)
• Updated README introduction

v0.4.0 - 16 December 2022

• Added extension methods to work with nullable types (T?)
  • From T? to fpdart's types
    • toOption
    • toEither
    • toTaskOption
    • toIOEither
    • toTaskEither
    • toTaskEitherAsync
    • fromNullable (Either, IOEither, TaskOption TaskEither)
    • fromNullableAsync (TaskEither)
  • From fpdart's types to T?
    • toNullable (Either)

/// [Option] <-> `int?`
int? value1 = 10.toOption().map((t) => t + 10).toNullable();

bool? value2 = value1?.isEven;

/// `bool?` -> [Either] -> `int?`
int? value3 = value2
    .toEither(() => "Error")
    .flatMap((a) => a ? right<String, int>(10) : left<String, int>("None"))
    .toNullable();

/// `int?` -> [Option]
Option<int> value4 = (value3?.abs().round()).toOption().flatMap(Option.of);

• Added toIOEither to Either
• Removed parameter from Either fromNullable [⚠️ BREAKING CHANGE]

final either = Either<String, int>.fromNullable(value, (r) => 'none');

/// 👆 Removed the value `(r)` (it was always null anyway 💁🏼‍♂️) 👇

final either = Either<String, int>.fromNullable(value, () => 'none');

• Added chainEither to TaskEither
• Added safeCast (Either and Option)
• Added safeCastStrict (Either and Option)

int intValue = 10;

/// Unhandled exception: type 'int' is not a subtype of type 'List<int>' in type cast
final waitWhat = intValue as List<int>;
final first = waitWhat.first;

/// Safe 🎯
final wellYeah = Either<String, List<int>>.safeCast(
  intValue,
  (dynamic value) => 'Not a List!',
);
final firstEither = wellYeah.map((list) => list.first);

• Added Open API Meteo example (from imperative to functional programming)
• Added new articles
  • Option type and Null Safety in dart
  • Either - Error Handling in Functional Programming
  • Future & Task: asynchronous Functional Programming
  • Flutter Supabase Functional Programming with fpdart
  • Open Meteo API - Functional programming with fpdart (Part 1)
  • Open Meteo API - Functional programming with fpdart (Part 2)

v0.3.0 - 11 October 2022

• Inverted onSome and onNone functions parameters in match method of Option [⚠️ BREAKING CHANGE] (Read more on why 👉 #56)

/// Everywhere you are using `Option.match` you must change this:
final match = option.match(
  (a) => print('Some($a)'),
  () => print('None'), // <- `None` second 👎 
);

/// to this (invert parameters order):
final match = option.match(
  () => print('None'), // <- `None` first 👍
  (a) => print('Some($a)'),
);

• Added traverse and sequence methods (#55)
  • traverseList
  • traverseListWithIndex
  • sequenceList
  • traverseListSeq
  • traverseListWithIndexSeq
  • sequenceListSeq

/// "a40" is invalid 💥
final inputValues = ["10", "20", "30", "a40"];

/// Verify that all the values can be converted to [int] 🔐
///
/// If **any** of them is invalid, then the result is [None] 🙅‍♂️
final traverseOption = inputValues.traverseOption(
  (a) => Option.tryCatch(
    /// If `a` does not contain a valid integer literal a [FormatException] is thrown
    () => int.parse(a),
  ),
);

• Added bindEither method in TaskEither (#58)

/// Chain [Either] to [TaskEither]
TaskEither<String, int> binding =
    TaskEither<String, String>.of("String").bindEither(Either.of(20));

• Added lefts, rights, and partitionEithers methods to Either (#57)

final list = [
  right<String, int>(1),
  right<String, int>(2),
  left<String, int>('a'),
  left<String, int>('b'),
  right<String, int>(3),
];
final result = Either.partitionEithers(list);
expect(result.first, ['a', 'b']);
expect(result.second, [1, 2, 3]);

• Added bimap method to Either, IOEither, and Tuple2 (#57)
• Added mapLeft method to IOEither (#57)
• Added fold method to Option (same as match) (#56)
• Fixed chainFirst for Either, TaskEither, and IOEither when chaining on a failure (Left) (#47) by DevNico 🎉
• Added const to all constructors in which it was missing (#59)
• Minimum environment dart sdk to 2.17.0 ⚠️

environment:
  sdk: ">=2.17.0 <3.0.0"

• Updated README and documentation

  • New tutorial articles
    • How to make API requests with validation in fpdart
    • How to use TaskEither in fpdart
    • Collection of tutorials on fpdart

• Testing improvements (internal)

  • Added testing utils
  • Added Property-based testing using glados
  • Fixed tests for match() method by adding fail in unexpected matched branch

• Contribution improvements

  • Added testing workflow with Github actions (#54)

v0.2.0 - 16 July 2022

• Refactoring for mixin breaking change (#42) by TimWhiting 🎉
• Added chainFirst method for the following classes (#39)
  • TaskEither
  • Either
  • IO
  • IOEither
  • State
  • StateAsync
  • Reader

v0.1.0 - 17 June 2022

• Added idFuture and identityFuture methods (#38) by f-person 🎉
• Added mapBoth method to Tuple2 (#30)
• Fixed linting warnings
• Fixed issue with upsert method for Map (#37) ⚠️
• Minimum environment dart sdk to 2.16.0 ⚠️

environment:
  sdk: ">=2.16.0 <3.0.0"

v0.0.14 - 31 January 2022

• Updated package linting to lints

v0.0.13 - 26 January 2022

• New methods to TaskEither, TaskOption, Either, and Option
  • mapLeft (TaskEither)
  • bimap (TaskEither)
  • toTaskEither (Either)
  • toTaskOption (Option)
• New Blog posts and tutorials section in README
  • New blog post How to map an Either to a Future in fpdart

v0.0.12 - 24 October 2021

• Completed IORef type implementation, documentation, and testing
  • Merged PR (#25) by purplenoodlesoop 🎉

v0.0.11 - 22 September 2021

• Fixed major issue in State and StateAsync implementation [BREAKING CHANGE]
  • Methods flatMap, map, map2, map3, ap, andThen, call, and flatten had an implementation issue that has been now fixed

v0.0.10 - 13 August 2021

• Released introduction to Practical Functional Programming
• Completed StateAsync type implementation, documentation, and testing
• Fixed problem with Alt typeclass (#21)
• Added call method to more easily chain functions in Monad and Monad2

v0.0.9 - 3 August 2021

• Released two new tutorials on the Option type:
  • Functional Programming Option type – Introduction
  • Chain functions using Option type – Functional Programming
• Added toJson and fromJson methods to Option to use json_serializable to convert Option type to and from Json (using @JsonSerializable)
• Added functional extension methods on Map
• Added composable Predicate type (and &, or |, not ~, xor ^) (#18)

v0.0.8 - 13 July 2021

• Released Part 3 of Fpdart, Functional Programming in Dart and Flutter
• Added Pure Functional Flutter app example (pokeapi_functional)
• Added flatMapTask and toTask methods to IO to lift and chain IO with Task
• Added flatMapTask and toTask methods to IOEither to lift and chain IOEither with TaskEither
• Added pattern matching extension methods to bool (boolean.dart)
• Added functions to get random int, double, and bool in a functional way (using IO) (random.dart)
• Added functions, extension methods, Ord, and Eq instances to DateTime (date.dart)

v0.0.7 - 6 July 2021

• Released Part 2 of Fpdart, Functional Programming in Dart and Flutter
• Added Compose and Compose2, used to easily compose functions in a chain
• Added curry and uncurry extensions on functions up to 5 parameters
• Completed TaskOption type implementation, documentation, and testing
• Expanded documentation and examples
• Added TaskEither.tryCatchK and Either.tryCatchK, by tim-smart (#10, #11) 🎉

v0.0.6 - 29 June 2021

• Released Part 1 of Fpdart, Functional Programming in Dart and Flutter
• Added functional extension methods on Iterable (List)
• Completed IOEither type implementation, documentation, and testing
• Added constF function
• Added option and optionOf (same as dartz)
• Added Either.right(r) factory constructor to Either class (same as Either.of(r)) (#3)
• Added example on reading local file using TaskEither (read_write_file)
• Added more examples
• Added constant constructors to Eq and variants, by mateusfccp (#4) 🎉

v0.0.5 - 20 June 2021

• Completed State type implementation, documentation, and testing
• Completed Reader type implementation, documentation, and testing
• Completed IO type implementation, documentation, and testing
• Merged PR (#2) by jacobaraujo7 🎉
  • Added right and left functions to create instance of Either
  • Added id function (same as identity)
  • Added fold method to Either (same as match)
  • Added bind method to Either (same as flatMap)
  • Added bindFuture method to Either, which returns TaskEither

v0.0.4 - 15 June 2021

• Completed Unit type documentation
• Completed Task type implementation, documentation, and testing
• Completed TaskEither type implementation, documentation, and testing
• Completed implementation, documentation, and testing of Foldable instance on Option and Either [BREAKING CHANGE]
• Completed Tuple2 type implementation, documentation, and testing [BREAKING CHANGE]
• Renamed fold method of Foldable to foldLeft [BREAKING CHANGE]
• Updated methods API (foldRight, foldLeft, etc.) of Foldable instances (Option, Either, Tuple) [BREAKING CHANGE]
• IList not longer working correctly (waiting for a better solution for immutable collections) [BREAKING CHANGE]

v0.0.3 - 13 June 2021

• Changed name of type Maybe to Option to be inline with fp-ts, cats, and dartz [BREAKING CHANGE]

v0.0.2 - 13 June 2021

First major release:

Types

• Either
• IList
• Maybe
• Reader
• State
• Task
• TaskEither
• Tuple
• Unit

Typeclasses

• Alt
• Applicative
• Band
• BoundedSemilattice
• CommutativeGroup
• CommutativeMonoid
• CommutativeSemigroup
• Eq
• Extend
• Filterable
• Foldable
• Functor
• Group
• Hash
• HKT
• Monad
• Monoid
• Order
• PartialOrder
• Semigroup
• Semilattice

Examples

• Either
• curry
• Maybe
• Reader
• State

v0.0.1 - 28 May 2021

• Eq
• Hash
• PartialOrder