public override HeronValue Eval(VM vm)
{
HeronValue val = vm.Eval(rvalue);
if (lvalue is Name)
{
string name = (lvalue as Name).name;
if (vm.HasVar(name))
{
vm.SetVar(name, val);
return(val);
}
else if (vm.HasField(name))
{
vm.SetField(name, val);
return(val);
}
else
{
throw new Exception(name + " is not a member field or local variable that can be assigned to");
}
}
else if (lvalue is ChooseField)
{
ChooseField field = lvalue as ChooseField;
HeronValue self = vm.Eval(field.self);
self.SetField(field.name, val);
return(val);
}
else if (lvalue is ReadAt)
{
ReadAt ra = lvalue as ReadAt;
HeronValue self = vm.Eval(ra.self);
HeronValue index = vm.Eval(ra.index);
ListValue list = self as ListValue;
if (list != null)
{
list.SetAtIndex(index, val);
return(val);
}
ArrayValue array = self as ArrayValue;
if (array != null)
{
array.SetAtIndex(index, val);
return(val);
}
throw new Exception("Unimplemented");
}
else
{
throw new Exception("Cannot assign to expression " + lvalue.ToString());
}
}
public static Expression CreatePostfixExpr(ParseNode x, ref int i)
{
int old = i;
Expression r = CreatePrimaryExpr(x, ref i);
Assure(x, r != null, "unable to create primary expression");
while (i < x.GetNumChildren())
{
old = i;
ParseNode tmp = x.GetChild(i);
if (tmp.Label == "bracketedexpr")
{
i++;
Assure(x, tmp.GetNumChildren() == 1, "brackets must contain only a single sub-expression");
r = new ReadAt(r, CreateExpr(tmp.GetChild(0)));
}
else if (tmp.Label == "paranexpr")
{
i++;
r = new FunCall(r, CreateCompoundExpr(tmp));
}
else if (tmp.ToString() == ".")
{
i++;
Assure(x, x.GetNumChildren() > i, "a '.' operator must be followed by a valid name expression");
tmp = x.GetChild(i);
Assure(x, tmp.Label == "name", "a '.' operator must be followed by a valid name expression");
string sName = tmp.ToString();
Assure(x, sName.Length > 0, "Name expression must have non-zero length");
i++;
r = new ChooseField(r, sName);
}
else if (tmp.ToString() == "++")
{
// You can't have anything to the left of ++
i++;
return(new PostIncExpr(r));
}
else
{
return(r);
}
Assure(x, i > 0, "internal error, failed to advance sub-expression index");
}
return(r);
}