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Implementing Brian Beckman's "Labeled Tree" example in Java 8
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README.md

BeckmanStateMonad - RELEASE 1.0

This is a Java 8 porting of the C# code prepared by Brian Beckman for his lesson about the state monad. The example involves traversing a binary tree with String leaves and substituting each String with an Integer, each time incremented by one.

I have created chainable monads, where each instance is characterised by a s2scp (State to State-Content Pair) java.util.Function and by an instance method bind; bind chains 'this' with a function which extracts the inner value of the present monad and produces a different StateMonad instance.

The only static method around is StateMonad.UNIT, which fulfills the role of 'return' in Haskell.

The repository features the following applications:

  • Manual Labeling of the tree, without use of the monad
  • Monadic Labeling of the tree, using the state monad - the attempt at using StateMonad.UNIT failed (*) and monads are created explicitly composing their s2scp functions as lambdas
  • RollDice, a simple composition of state monads created from scratch
  • attempt at demonstrating the three monad laws in the case of this implementation - some problems still on the way

This repository is presented at:

http://faustinelli.wordpress.com/2014/04/25/the-state-monad-in-java-8-eventually/

STILL TO DO

  • implementation of getState and putState
  • further experiences to get a feel of the application of the monad
  • (*) SOLVE ALL PROBLEMS WITH UNIT in ManualLabeling.java - apparently the substitution from StateMonad<S,B> into StateMonad<Integer,Tr<Scp<Integer,String>>> can't be managed by the compiler.

DEBITS AND CREDITS

I am in debt with:

Any feedback is welcome.


Released under MIT License.

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