com.github.tonivade.purefun.instances.StateInstances Maven / Gradle / Ivy

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/*
 * Copyright (c) 2018-2022, Antonio Gabriel Muñoz Conejo 
 * Distributed under the terms of the MIT License
 */
package com.github.tonivade.purefun.instances;

import static com.github.tonivade.purefun.Unit.unit;
import com.github.tonivade.purefun.Function1;
import com.github.tonivade.purefun.Kind;
import com.github.tonivade.purefun.Tuple;
import com.github.tonivade.purefun.Unit;
import com.github.tonivade.purefun.data.ImmutableList;
import com.github.tonivade.purefun.monad.State;
import com.github.tonivade.purefun.monad.StateOf;
import com.github.tonivade.purefun.monad.State_;
import com.github.tonivade.purefun.typeclasses.Console;
import com.github.tonivade.purefun.typeclasses.Monad;
import com.github.tonivade.purefun.typeclasses.MonadState;

@SuppressWarnings("unchecked")
public interface StateInstances {

  static  Monad> monad() {
    return StateMonad.INSTANCE;
  }

  static  MonadState, S> monadState() {
    return StateMonadState.INSTANCE;
  }

  static Console>> console() {
    return StateConsole.INSTANCE;
  }
}

interface StateMonad extends Monad> {

  @SuppressWarnings("rawtypes")
  StateMonad INSTANCE = new StateMonad() {};

  @Override
  default  State pure(T value) {
    return State.pure(value);
  }

  @Override
  default  State flatMap(Kind, ? extends T> value,
      Function1, ? extends R>> map) {
    return StateOf.narrowK(value).flatMap(map.andThen(StateOf::narrowK));
  }
}

interface StateMonadState extends MonadState, S>, StateMonad {

  @SuppressWarnings("rawtypes")
  StateMonadState INSTANCE = new StateMonadState() {};

  @Override
  default State get() {
    return State.get();
  }

  @Override
  default State set(S state) {
    return State.set(state);
  }
}

final class StateConsole implements Console>> {

  protected static final StateConsole INSTANCE = new StateConsole();

  @Override
  public State, String> readln() {
    return State.state(list -> Tuple.of(list.tail(), list.head().getOrElseThrow()));
  }

  @Override
  public State, Unit> println(String text) {
    return State.state(list -> Tuple.of(list.append(text), unit()));
  }
}