Java仿haskell

本文主要是介绍Java仿haskell，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

Functor函子

package cn.lyf.fx;

import java.util.*;
import java.util.function.*;

//集成了Either函子
public class Functor {
    private Object value;

    protected Functor(Object val) {
        value = val;
    }

    /// Pointed///产生个函子
    public static Functor of(Object val) {
        return new Functor(val);
    }

    // 范畴间映射变换
    public <T, R> Functor map(Function<T, R> fx) {
        return innerMap(value, fx);
    }

    @SuppressWarnings("unchecked")
    protected <T, R> Functor innerMap(Object o, Function<T, R> fx) {
        try {
            /// Either/
            if (o instanceof Exception)
                return this;
            R r = fx.apply((T) o);
            return of(r);
        } catch (Exception e) {
            return of(e);
        }
    }

    // 获取被包装的value
    public Functor unpack() {
        while (value instanceof Functor) {
            value = ((Functor) value).value;
        }
        return of(value);
    }

    public Object getValue() {
        return value;
    }

    static class composeFunction<T, E, R> implements Function<T, R> {
        Function<T, E> f;
        Function<E, R> g;

        composeFunction(Function<T, E> f, Function<E, R> g) {
            this.f = f;
            this.g = g;
        }

        @Override
        public R apply(T t) {
            return g.apply(f.apply(t));
        }
    }

    // 复合函数
    public static <T, E, R> Function<T, R> compose(final Function<T, E> f, final Function<E, R> g) {
        return new composeFunction<T, E, R>(f, g);
    }

    static class Currying<R> implements Function<Object, Object> {
        List<Object> avgs;
        Function<Object[], R> fx;
        boolean run;

        Currying(List<Object> avgs, Function<Object[], R> fx) {
            this.avgs = avgs;
            this.fx = fx;
        }

        @Override
        public Object apply(Object t) {
            if (run)
                return fx.apply(avgs.toArray());
            avgs.add(t);
            return new Currying<>(avgs, fx);
        }
    }

    // 柯里化
    public static <R> Function<Object, Object> currying(Function<Object[], Function<Object[], R>> f) {
        return new Function<Object, Object>() {
            @Override
            public Object apply(Object t) {
                List<Object> avgs = new LinkedList<>();
                avgs.add(t);
                return new Currying<>(avgs, f);
            }
        };
    }

    public Functor end() {
        Currying<?> curry = (Currying<?>) value;
        curry.run = true;
        return of(curry.apply(null));
    }

    // Monad///
    public <T, R> Functor flatMap(Function<T, R> fx) {
        return this.map(fx).join();
    }

    public Functor join() {
        if (value == null || !(value instanceof Functor))
            return this;
        return (Functor) value;
    }

    // Maybe
    public <T, R> Functor Maybe(Function<T, R> fx) {
        if (value == null)
            return this;
        return innerMap(value, fx);
    }

    // Applicative//value是函数，返回一个中间态函子
    public Functor ap(Object box) {
        Function<?, ?> fx = (Function<?, ?>) value;
        return of(box).map(fx);
    }

    @Override
    public String toString() {
        return "{" + value.toString() + "}";
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof Functor) {
            return ((Functor) obj).value.equals(value);
        }
        return false;
    }

    @Override
    public int hashCode() {
        if (value != null)
            return value.hashCode();
        return 0;
    }
}

IO 函子

package cn.lyf.fx;

import java.util.function.*;
import java.io.*;

public class IO extends Functor {
    IO(Object fx) {
        super(fx);
    }

    public static IO of(String str) {
        return new IO(str);
    }

    public static Function<String, String> scan = new Function<>() {
        public String apply(String path) {
            try (FileInputStream fis = new FileInputStream(path);
                    InputStreamReader isr = new InputStreamReader(fis, "UTF-8");
                    BufferedReader br = new BufferedReader(isr);) {
                String line = null;
                StringBuffer sb = new StringBuffer();
                while ((line = br.readLine()) != null) {
                    sb.append(line);
                    sb.append("\n");
                }
                return sb.toString();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return null;
        };
    };

    public static Function<String, String> print = new Function<>() {
        public String apply(String str) {
            System.out.println(str);
            return str;
        };
    };
}

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