Getval {
	var <obj, <func;
	
	*new {arg obj, func;
		^super.newCopyArgs(obj).init(func);
		}
		
	init {arg thisfunc;
		thisfunc.isNil.if({
			case
				{obj.isKindOf(Env)} {func = \at}
				{obj.isKindOf(InterplEnv)} {func = \at}
				{obj.isKindOf(Stream)} {func = \next}
				{obj.isKindOf(SequenceableCollection)} {func = \at}
				{true} {func = \value}
			});
		}
		
	cur {arg time = 0, index = 0;
		^obj.perform(func, time, index);
		}

	obj_ {arg newobj, newfunc;
		obj = newobj;
		func = newfunc;
		this.init;
		}
		
	func_ {arg newfunc;
		func = newfunc;
		this.init;
		}
}