src/jrw/Environment.java

   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(null);
   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 }