package bjc.funcdata.theory;

import java.util.function.Function;

/**
 * Represents a container or context some sort usually, but the precise
 * definition is that it represents exactly what it is defined as.
 *
 * @author ben
 *
 * @param <ContainedType>
 *                        The value inside the functor.
 */
public interface Functor<ContainedType> {
	/**
	 * Converts a normal function to operate over values in a functor..
	 *
	 * N.B: Even though the type signature implies that you can apply the resulting
	 * function to any type of functor, it is only safe to call it on instances of
	 * the type of functor you called fmap on..
	 *
	 * @param <ArgType>
	 *                     The argument of the function.
	 *
	 * @param <ReturnType>
	 *                     The return type of the function.
	 *
	 * @param func
	 *                     The function to convert.
	 *
	 * @return The passed in function converted to work over a particular type of
	 *         functors.
	 */
	public <ArgType, ReturnType> Function<Functor<ArgType>, Functor<ReturnType>>
			fmap(Function<ArgType, ReturnType> func);

	/**
	 * Retrieve the thing inside this functor.
	 *
	 * @return The thing inside this functor.
	 */
	public ContainedType getValue();
}