PSetter.java

package fj.data.optic;

import fj.F;
import fj.Function;
import fj.data.Either;

/**
 * A {@link PSetter} is a generalisation of Functor map: - `map: (A => B) => F[A] => F[B]` - `modify: (A => B) => S =>
 * T`
 *
 * {@link PSetter} stands for Polymorphic Setter as it set and modify methods change a type `A` to `B` and `S` to `T`.
 *
 * {@link PTraversal}, {@link POptional}, {@link PPrism}, {@link PLens} and {@link PIso} are valid {@link PSetter}
 *
 * @param <S> the source of a {@link PSetter}
 * @param <T> the modified source of a {@link PSetter}
 * @param <A> the target of a {@link PSetter}
 * @param <B> the modified target of a {@link PSetter}
 */
public abstract class PSetter<S, T, A, B> {

  PSetter() {
    super();
  }

  /** modify polymorphically the target of a {@link PSetter} with a function */
  public abstract F<S, T> modify(F<A, B> f);

  /** set polymorphically the target of a {@link PSetter} with a value */
  public abstract F<S, T> set(final B b);

  /** join two {@link PSetter} with the same target */
  public final <S1, T1> PSetter<Either<S, S1>, Either<T, T1>, A, B> sum(final PSetter<S1, T1, A, B> other) {
    return pSetter(f -> e -> e.bimap(modify(f), other.modify(f)));
  }

  /*************************************************************/
  /** Compose methods between a {@link PSetter} and another Optics */
  /*************************************************************/

  /** compose a {@link PSetter} with a {@link PSetter} */
  public final <C, D> PSetter<S, T, C, D> composeSetter(final PSetter<A, B, C, D> other) {
    final PSetter<S, T, A, B> self = this;
    return new PSetter<S, T, C, D>() {

      @Override
      public F<S, T> modify(final F<C, D> f) {
        return self.modify(other.modify(f));
      }

      @Override
      public F<S, T> set(final D d) {
        return self.modify(other.set(d));
      }
    };
  }

  /** compose a {@link PSetter} with a {@link PTraversal} */
  public final <C, D> PSetter<S, T, C, D> composeTraversal(final PTraversal<A, B, C, D> other) {
    return composeSetter(other.asSetter());
  }

  /** compose a {@link PSetter} with a {@link POptional} */
  public final <C, D> PSetter<S, T, C, D> composeOptional(final POptional<A, B, C, D> other) {
    return composeSetter(other.asSetter());
  }

  /** compose a {@link PSetter} with a {@link PPrism} */
  public final <C, D> PSetter<S, T, C, D> composePrism(final PPrism<A, B, C, D> other) {
    return composeSetter(other.asSetter());
  }

  /** compose a {@link PSetter} with a {@link PLens} */
  public final <C, D> PSetter<S, T, C, D> composeLens(final PLens<A, B, C, D> other) {
    return composeSetter(other.asSetter());
  }

  /** compose a {@link PSetter} with a {@link PIso} */
  public final <C, D> PSetter<S, T, C, D> composeIso(final PIso<A, B, C, D> other) {
    return composeSetter(other.asSetter());
  }

  public static <S, T> PSetter<S, T, S, T> pId() {
    return PIso.<S, T> pId().asSetter();
  }

  public static <S, T> PSetter<Either<S, S>, Either<T, T>, S, T> pCodiagonal() {
    return pSetter(f -> e -> e.bimap(f, f));
  }

  public static <S, T, A, B> PSetter<S, T, A, B> pSetter(final F<F<A, B>, F<S, T>> modify) {
    return new PSetter<S, T, A, B>() {
      @Override
      public F<S, T> modify(final F<A, B> f) {
        return modify.f(f);
      }

      @Override
      public F<S, T> set(final B b) {
        return modify.f(Function.constant(b));
      }
    };
  }
}