Install some basic error handling in Dispatch.

[jrw.git] / src / jrw / Environment.java

package jrw;

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

public class Environment {
    public static final Environment root = new Environment(null);
    private static final ThreadLocal<Environment> current = new ThreadLocal<>();
    public final Environment parent;
    private Map<Variable<?>, Object> data = Collections.emptyMap();

    public static class Variable<T> {
	private final Supplier<? extends T> ival;
	private T rval;
	private boolean inited;

	public Variable(Supplier<? extends T> ival) {
	    this.ival = ival;
	}

	@SuppressWarnings("unchecked")
	public T get() {
	    for(Environment env = current(); env != null; env = env.parent) {
		Map<Variable<?>, Object> data = env.data;
		if(data.containsKey(this))
		    return((T)data.get(this));
	    }
	    if(!inited) {
		synchronized(this) {
		    if(!inited) {
			rval = (this.ival == null) ? null : this.ival.get();
			inited = true;
		    }
		}
	    }
	    return(rval);
	}
    }

    public Environment(Environment parent) {
	this.parent = parent;
    }

    public Environment() {
	this(current());
    }

    public <T> void set(Variable<T> var, T val) {
	synchronized(this) {
	    Map<Variable<?>, Object> data = new IdentityHashMap<>(this.data);
	    data.put(var, val);
	    this.data = data;
	}
    }

    public <T> void clear(Variable<T> var, T val) {
	synchronized(this) {
	    Map<Variable<?>, Object> data = new IdentityHashMap<>(this.data);
	    data.remove(var);
	    this.data = data;
	}
    }

    public static Environment current() {
	Environment ret = current.get();
	return((ret == null) ? root : ret);
    }

    public class Frame implements AutoCloseable {
	private final Environment prev;

	private Frame() {
	    this.prev = current.get();
	    current.set(Environment.this);
	}

	public void close() {
	    current.set(prev);
	}
    }

    public Frame frame() {
	return(new Frame());
    }
}