serene-simple/src/main/java/serene/simple/ListNode.java

/**
 * Serene (simple) - A PoC lisp to collect data on Serenes concepts
 * Copyright (C) 2019-2020 Sameer Rahmani <lxsameer@gnu.org>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA  02110-1301, USA.
 */
package serene.simple;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.function.Function;

import serene.simple.builtin.AFn;

import static java.util.Arrays.asList;

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

public class ListNode<T extends Node> extends Node implements Iterable<T> {
  public static final ListNode<?> EMPTY = new ListNode<>();

  public final T first;
  public final ListNode<T> rest;
  public final int length;

  public ListNode() {
    this.first = null;
    this.rest = null;
    this.length = 0;
  }

  public ListNode(T f, ListNode<T> r) {
    this.first = f;
    this.rest = r;
    this.length = r.length + 1;
  }

  @SafeVarargs
  public static <T extends Node> ListNode<T> list(T... objs) {
    return list(asList(objs));
  }

  public static <T extends Node> ListNode<T> list(List<T> objs) {
    ListNode<T> l = (ListNode<T>) EMPTY;
    for (int i = objs.size() - 1; i >= 0; i--) {
      l = l.cons(objs.get(i));
    }
    return l;
  }

  public ListNode<T> cons(T node) {
    return new ListNode<T>(node, this);
  }

  @Override
  public Object eval(BaseScope scope) {
    SymbolNode firstElement = (SymbolNode) this.first();
    List<Object> args = new ArrayList<Object>();

    for (T node : this.rest()) {
      args.add(node.eval(scope));
    }

    if (firstElement.name.startsWith(".")) {
      return this.evalInterop(scope, firstElement, args.subList(1, args.size()));
    }

    Object f = firstElement.eval(scope);
    if (f instanceof AFn) {
      return evalBuiltin(scope, (AFn) f, args);
    }
    else {
      return evalFn(scope, (Function<Object, Object>) f, args);
    }
  }

  public Object evalBuiltin(BaseScope scope, AFn fn, List<Object> args) {
    fn.setArguments(args);
    return fn.eval(scope);
  }

  public Object evalFn(BaseScope scope, Function<Object, Object> fn, List<Object> args) {
    return fn.apply(args.toArray());
  }

  public Object evalInterop(BaseScope scope, SymbolNode firstElement, List<Object> rest)
    throws SereneException {

    String mName = firstElement.name.substring(1, firstElement.name.length());
    Object target = this.rest().first().eval(scope);

    if (mName.startsWith("-")) {
      return this.evalInteropProperty(
        scope,
        target,
        mName.substring(1, mName.length()));
    }

    try {
      Method f = target.getClass().getMethod(mName);
      return f.invoke(target, rest.toArray());
    }

    catch(NoSuchMethodException e) {
      throw new SereneException(
        String.format(
          "Can't find method '%s' on object '%s'.",
          mName,
          this.rest().first()));
    }
    catch (InvocationTargetException e) {
      Throwable cause = e.getCause();
      throw new SereneException(
        String.format(
          "Invocation of '%s' failed because of: %s%n",
          mName, cause.getMessage()));
    }
    catch (IllegalAccessException e) {
      throw new SereneException(
        String.format("Illegal access from '%s'", mName));
    }
  }

  public Object evalInteropProperty(BaseScope scope, Object target, String propertyName)
    throws SereneException {

    try {
      Class<?> targetClass = this.getClassOf(target);
      return targetClass.getField(propertyName);
    }
    catch(NoSuchFieldException e) {
      throw new SereneException(
        String.format(
          "Can't find field '%s' on object '%s'.",
          propertyName,
          target.toString()));
    }
  }

  public T first() {
    if (this != EMPTY) {
      return this.first;
    }
    return null;
  }

  public ListNode<T> rest() {
    if (this != EMPTY) {
      return this.rest;
    }
    return (ListNode<T>) EMPTY;
  }


  @Override
  public Iterator<T> iterator() {
    return new Iterator<T>() {
      private ListNode<T> l = ListNode.this;

      @Override
      public boolean hasNext() {
        return this.l != EMPTY;
      }

      @Override
      public T next() {
        if (this.l == EMPTY) {
          return null;
        }
        T first = this.l.first;
        this.l = this.l.rest;
        return first;
      }

      @Override
      public void remove() {
        throw new SereneException("Iterator is immutable");
      }
    };
  }

  public String toString() {
    if (this.length == 0) {
      return "()";
    }

    String output = "(" + this.first();
    for(Node x : this.rest()) {
      output = output + " " + x.toString();
    }

    return output + ")";
  }

  private Class<?> getClassOf(Object target) {
      if (target instanceof Class) {
        return (Class<?>) target;
      }

      return target.getClass();
  }
}