concepts 0.2.0

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Concepts is a partial port of Haskell's type class hierarchy to Dart. This library contains interfaces only with no implementations. This allows us to leverage Dart's type checker in conjunction with Dart's package manager to create executable, versioned and linkable specifications which double as layers of interoperation via polymorphism.

Like the algebraic structures in the haskell type class hierarchy, each given implementation must satisfy the interface as well as satisfy the laws associated to that interface.



SemiGroup represents data structures which can be merged associatively. Some people get an intuition from this by saying that it's two structures which can be summed.


  1. Associativity: a.merge(b).merge(c) is equivalent to a.merge(b.merge(c))


A Monoid is a SemiGroup that also implements an identity value.


  1. Right identity: m.merge(m.empty()) is equivalent to m
  2. Left identity: m.empty().merge(m) is equivalent to m
  3. Must also implement the SemiGroup laws (associativity).


A functor is a structure which wraps a value and comes with a structure preserving operations which allows you to transition the inner value to a new state. This structure preserving operation is known as map.


  1. Identity: => a) is equivalent to u
  2. Composition: => f(g(x))) is equivalent to


Applicative is a Functor lets you apply a function that is contained in a context itself to values that are also in the context.


  1. Identity: const A((a) => a).ap(v) is equivalent to v
  2. Homomorphism: const A(f).ap(const A(x)) is equivalent to const A(f(x))
  3. Interchange: u.ap(const A(y)) is equivalent to const A((f) => f(y)).ap(u)
  4. Must also implement the Functor laws.


A monad is an applicative functor that lets you transition a value to a new context within the same type hierarchy.


  1. Left identity: const M(a).expand(f) is equivalent to f(a)
  2. Right identity: m.expand((n) => const M(n)) is equivalent to m
  3. Must also implement the Applicative laws.

1. Depend on it

Add this to your package's pubspec.yaml file:

  concepts: "^0.2.0"

2. Install it

You can install packages from the command line:

with pub:

$ pub get

with Flutter:

$ flutter packages get

Alternatively, your editor might support pub get or packages get. Check the docs for your editor to learn more.

3. Import it

Now in your Dart code, you can use:

import 'package:concepts/concepts.dart';
Version Uploaded Documentation Archive
0.2.0 Aug 19, 2014 Go to the documentation of concepts 0.2.0 Download concepts 0.2.0 archive
0.1.0 Aug 19, 2014 Go to the documentation of concepts 0.1.0 Download concepts 0.1.0 archive


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More details: scoring.

We analyzed this package, and provided a score, details, and suggestions below.

  • completed on Feb 3, 2018
  • Dart: 2.0.0-dev.20.0
  • pana: 0.10.1


Describes how popular the package is relative to other packages. [more]
9 / 100
Code health derived from static analysis. [more]
91 / 100
Reflects how tidy and up-to-date the package is. [more]
0 / 100
Overall score:
Weighted score of the above. [more]


Detected platforms: Flutter, web, other

No platform restriction found in primary library package:concepts/concepts.dart.


  • Maintain

    Changelog entries help clients to follow the progress in your code.

  • Package is pre-v1 release.

    While there is nothing inherently wrong with versions of 0.*.*, it usually means that the author is still experimenting with the general direction API.

  • Maintain an example.

    Create a short demo in the example/ directory to show how to use this package. Common file name patterns include: main.dart, example.dart or you could also use concepts.dart.