| 1 | package jrw; |
| 2 | |
| 3 | import java.util.*; |
| 4 | import java.util.function.*; |
| 5 | |
| 6 | public class Environment { |
| 7 | public static final Environment root = new Environment(); |
| 8 | private static final ThreadLocal<Environment> current = new ThreadLocal<>(); |
| 9 | public final Environment parent; |
| 10 | private Map<Variable<?>, Object> data = Collections.emptyMap(); |
| 11 | |
| 12 | public static class Variable<T> { |
| 13 | private final Supplier<? extends T> ival; |
| 14 | private T rval; |
| 15 | private boolean inited; |
| 16 | |
| 17 | public Variable(Supplier<? extends T> ival) { |
| 18 | this.ival = ival; |
| 19 | } |
| 20 | |
| 21 | @SuppressWarnings("unchecked") |
| 22 | public T get() { |
| 23 | for(Environment env = current(); env != null; env = env.parent) { |
| 24 | Map<Variable<?>, Object> data = env.data; |
| 25 | if(data.containsKey(this)) |
| 26 | return((T)data.get(this)); |
| 27 | } |
| 28 | if(!inited) { |
| 29 | synchronized(this) { |
| 30 | if(!inited) { |
| 31 | rval = (this.ival == null) ? null : this.ival.get(); |
| 32 | inited = true; |
| 33 | } |
| 34 | } |
| 35 | } |
| 36 | return(rval); |
| 37 | } |
| 38 | } |
| 39 | |
| 40 | public Environment(Environment parent) { |
| 41 | this.parent = parent; |
| 42 | } |
| 43 | |
| 44 | public Environment() { |
| 45 | this(current()); |
| 46 | } |
| 47 | |
| 48 | public <T> void set(Variable<T> var, T val) { |
| 49 | synchronized(this) { |
| 50 | Map<Variable<?>, Object> data = new IdentityHashMap<>(this.data); |
| 51 | data.put(var, val); |
| 52 | this.data = data; |
| 53 | } |
| 54 | } |
| 55 | |
| 56 | public <T> void clear(Variable<T> var, T val) { |
| 57 | synchronized(this) { |
| 58 | Map<Variable<?>, Object> data = new IdentityHashMap<>(this.data); |
| 59 | data.remove(var); |
| 60 | this.data = data; |
| 61 | } |
| 62 | } |
| 63 | |
| 64 | public static Environment current() { |
| 65 | Environment ret = current.get(); |
| 66 | return((ret == null) ? root : ret); |
| 67 | } |
| 68 | |
| 69 | public class Frame implements AutoCloseable { |
| 70 | private final Environment prev; |
| 71 | |
| 72 | private Frame() { |
| 73 | this.prev = current.get(); |
| 74 | current.set(Environment.this); |
| 75 | } |
| 76 | |
| 77 | public void close() { |
| 78 | current.set(prev); |
| 79 | } |
| 80 | } |
| 81 | |
| 82 | public Frame frame() { |
| 83 | return(new Frame()); |
| 84 | } |
| 85 | } |