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# Jaffar, the Evil Advisor Library
#
# This is a simple experiment in Ruby metaprogmming, to see how to implement
# a lisp-style advising construct. Advising is basically augmenting existing
# functions with your own code. See the exemple below.
#
# Advising is very much related to context-oriented programming. I fortunately
# have no use for either an advising or context-oriented programming right now
# and this is why I did not expand upon this simple implementation.
#

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package util;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

/**
 * This class implements multiple dispatch (aka multimethods) using reflection.
 * The idea is to choose the method based not only on the runtime type of the
 * receiver, but also on the runtime type of the arguments. Normally Java
 * selects amongst overloaded alternatives using the static type.

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// Basic setup

interface Exp
data class Lit(val x: Int): Exp
data class Add(val x: Exp, val y: Exp): Exp

interface IntAlg<A>
{
    fun lit(x: Int): A
    fun add(x: A, y: A): A

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// Basic setup

interface Exp
data class Lit(val x: Int): Exp
data class Add(val x: Exp, val y: Exp): Exp

val exp0 = Add(Lit(42), Lit(0x52))

// Adding a print operation

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As VirtualBox Guest

Networking

In the VM properties, make two connections: a "NAT" for regular internet connectivity, and a "host-only" for ssh connectivity between host and guest with a predictable IP. For this to work, both a NAT adapter and a host-only adapter have to be created in the host via the VirtualBox global preferences.

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inline fun <T, U> (() -> T?).map (crossinline f: (T) -> U): (() -> U?)
{
    return { this()?.let(f) }
}

inline fun <T> (() -> T?).filter (crossinline pred: (T) -> Boolean): (() -> T?)
{
    return {
        var out = this()
        while (out != null && !pred(out)) out = this()

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### Keybase proof

I hereby claim:

  * I am norswap on github.
  * I am norswap (https://keybase.io/norswap) on keybase.
  * I have a public key whose fingerprint is CB7E 4E0F F8C0 2860 6A62  55F2 A7E2 9E43 45FB 1D8E

To claim this, I am signing this object:

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macOS / OS X

Install homebrew then run brew install swi-prolog. You can now run the Prolog shell from the command line with swipl.

Important: do not install from the official website, you will get crashes.

Windows

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package demo;

public interface Node {}

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public final class Visitors
{
    // ---------------------------------------------------------------------------------------------
    // 1. Initial setup.

    interface Visitor {
        void visit (A object);
        void visit (B object);
    }