private TiState Step(TiState state)
{
var headAddr = state.Stack.Peek();
var headNode = state.Heap[headAddr];
return(headNode switch
{
TiNode.Number number => StepNum(state, number),
TiNode.Application application => StepAp(state, application),
TiNode.Supercombinator supercombinator => StepSc(state, supercombinator),
TiNode.Indirection indirection => StepInd(state, indirection),
TiNode.Primitive primitive => StepPrim(state, primitive),
TiNode.Data data => StepData(state, data),
_ => throw new ArgumentOutOfRangeException(nameof(headNode))
});
private static (ImmutableDictionary <int, TiNode>, int) MarkFrom(ImmutableDictionary <int, TiNode> heap, int addr)
{
var node = heap[addr];
switch (node)
{
case TiNode.Application application:
int function, argument;
(heap, function) = MarkFrom(heap, application.Function);
(heap, argument) = MarkFrom(heap, application.Argument);
node = new TiNode.Application(function, argument);
break;
case TiNode.Data data:
var components = new List <int>();
foreach (var component in data.Components)
{
int newComponent;
(heap, newComponent) = MarkFrom(heap, component);
components.Add(newComponent);
}
node = new TiNode.Data(data.Tag, components);
break;
case TiNode.Indirection indirection: return(MarkFrom(heap, indirection.Address));
case TiNode.Number _: break;
case TiNode.Primitive _: break;
case TiNode.Supercombinator _: break;
case Marked _: return(heap, addr);
default: throw new ArgumentOutOfRangeException(nameof(node));
}
heap = heap.SetItem(addr, new Marked(node));
return(heap, addr);
}