public INode Get(string key)
{
if (Parent == null)
{
return(GetShallow(key));
}
return(GetShallow(key) ?? Parent.Get(key));
}
private INode VisitSymbolNode(SymbolNode node, Environment env)
{
while (true)
{
var nullable = env.Get(node.Value);
if (nullable == null)
{
return(node);
}
if (nullable.GetType() != typeof(SymbolNode))
{
return(nullable);
}
node = (SymbolNode)nullable;
}
}
private INode BuiltinSet(List <INode> args, Environment env)
{
var first = (QuotedExpressionNode)args[0];
var second = (IntegerNode)args[1];
var third = args[2];
if (first.Children.Count != 1)
{
return(new ErrorNode("expected singleton array"));
}
var child = first.Children[0];
if (child.GetType() != typeof(SymbolNode))
{
return(new ErrorNode("expected singleton array to contain a symbol"));
}
var definition = env.Get(((SymbolNode)child).Value);
if (definition?.GetType() != typeof(QuotedExpressionNode))
{
return(new ErrorNode("symbol must be bound to an array"));
}
var array = (QuotedExpressionNode)definition;
var index = second.Value;
var replacement = third;
if (index < 0 || index >= array.Children.Count)
{
return(new ErrorNode("index is out of bounds"));
}
array.Children[index] = replacement;
return(Null);
}