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petitparser/lib/src/lisp/environment.dart

-part of lisp;
-
-/**
- * Environment of bindings.
- */
-class Environment {
-
-  /** The owning environment. */
-  final Environment _owner;
-
-  /** The internal environment bindings. */
-  final Map<Name, dynamic> _bindings;
-
-  /** Constructor for the nested environment. */
-  Environment([this._owner]) : _bindings = new Map();
-
-  /** Constructor for a nested environment. */
-  Environment create() => new Environment(this);
-
-  /** Return the binding for [key]. */
-  operator [](Name key) {
-    if (_bindings.containsKey(key)) {
-      return _bindings[key];
-    } else if (_owner != null) {
-      return _owner[key];
-    } else {
-      return _invalidBinding(key);
-    }
-  }
-
-  /** Updates the binding for [key] with a [value]. */
-  void operator []=(Name key, value) {
-    if (_bindings.containsKey(key)) {
-      _bindings[key] = value;
-    } else if (_owner != null) {
-      _owner[key] = value;
-    } else {
-      _invalidBinding(key);
-    }
-  }
-
-  /** Defines a new binding from [key] to [value]. */
-  define(Name key, value) {
-    return _bindings[key] = value;
-  }
-
-  /** Returns the keys of the bindings. */
-  Iterable<Name> get keys => _bindings.keys;
-
-  /** Returns the parent of the bindings. */
-  Environment get owner => _owner;
-
-  /** Called when a missing binding is accessed. */
-  _invalidBinding(Name key) {
-    throw new ArgumentError('Unknown binding for $key');
-  }
-}