Resolve "Re-Implement Evaluation"

Closes #75 (closed)

b_asic/signal_flow_graph.py

@@ -3,17 +3,20 @@ B-ASIC Signal Flow Graph Module.
 TODO: More info.
 """
 
-from typing import List, Iterable, Sequence, Dict, Optional, DefaultDict, MutableSet
+from typing import List, Iterable, Sequence, Dict, Optional, DefaultDict, MutableSet, Tuple
 from numbers import Number
 from collections import defaultdict, deque
 
 from b_asic.port import SignalSourceProvider, OutputPort
-from b_asic.operation import Operation, AbstractOperation, ResultKey, DelayMap, MutableResultMap, MutableDelayMap
+from b_asic.operation import Operation, AbstractOperation, ResultKey, DelayMap, MutableResultMap, MutableDelayMap, ResultKey
 from b_asic.signal import Signal
 from b_asic.graph_component import GraphID, GraphIDNumber, GraphComponent, Name, TypeName
 from b_asic.special_operations import Input, Output
 
 
+DelayQueue = List[Tuple[str, ResultKey, OutputPort]]
+
+
 class GraphIDGenerator:
     """A class that generates Graph IDs for objects."""
 
@@ -173,7 +176,7 @@ class SFG(AbstractOperation):
                 else:
                     output_string += "-, "
                 
-                if component.type_name is "c":
+                if component.type_name == "c":
                     output_string += "value: " + str(component.value) + ", input: ["
                 else:
                     output_string += "input: [" 
@@ -230,7 +233,13 @@ class SFG(AbstractOperation):
         for op, arg in zip(self._input_operations, self.truncate_inputs(input_values, bits_override) if truncate else input_values):
             op.value = arg
         
-        value = self._evaluate_source(self._output_operations[index].input(0).signals[0].source, results, delays, prefix, bits_override, truncate)
+        deferred_delays = []
+        value = self._evaluate_source(self._output_operations[index].input(0).signals[0].source, results, delays, prefix, bits_override, truncate, deferred_delays)
+        while deferred_delays:
+            new_deferred_delays = []
+            for key_base, key, src in deferred_delays:
+                self._do_evaluate_source(key_base, key, src, results, delays, prefix, bits_override, truncate, new_deferred_delays)
+            deferred_delays = new_deferred_delays
         results[self.key(index, prefix)] = value
         return value
 
@@ -422,22 +431,26 @@ class SFG(AbstractOperation):
         # The old SFG will be deleted by Python GC
         return self()
 
-    def _evaluate_source(self, src: OutputPort, results: MutableResultMap, delays: MutableDelayMap, prefix: str, bits_override: Optional[int], truncate: bool) -> Number:
-        src_prefix = prefix
-        if src_prefix:
-            src_prefix += "."
-        src_prefix += src.operation.graph_id
-
-        key = src.operation.key(src.index, src_prefix)
+    def _evaluate_source(self, src: OutputPort, results: MutableResultMap, delays: MutableDelayMap, prefix: str, bits_override: Optional[int], truncate: bool, deferred_delays: DelayQueue) -> Number:
+        key_base = (prefix + "." + src.operation.graph_id) if prefix else src.operation.graph_id
+        key = src.operation.key(src.index, key_base)
         if key in results:
             value = results[key]
             if value is None:
-                raise RuntimeError(f"Direct feedback loop detected when evaluating operation.")
+                raise RuntimeError("Direct feedback loop detected when evaluating operation.")
             return value
+        
+        value = src.operation.current_output(src.index, delays, key_base)
+        results[key] = value
+        if value is None:
+            value = self._do_evaluate_source(key_base, key, src, results, delays, prefix, bits_override, truncate, deferred_delays)
+        else:
+            deferred_delays.append((key_base, key, src)) # Evaluate later. Use current value for now.
+        return value
 
-        results[key] = src.operation.current_output(src.index, delays, src_prefix)
-        input_values = [self._evaluate_source(input_port.signals[0].source, results, delays, prefix, bits_override, truncate) for input_port in src.operation.inputs]
-        value = src.operation.evaluate_output(src.index, input_values, results, delays, src_prefix, bits_override, truncate)
+    def _do_evaluate_source(self, key_base: str, key: ResultKey, src: OutputPort, results: MutableResultMap, delays: MutableDelayMap, prefix: str, bits_override: Optional[int], truncate: bool, deferred_delays: DelayQueue) -> Number:
+        input_values = [self._evaluate_source(input_port.signals[0].source, results, delays, prefix, bits_override, truncate, deferred_delays) for input_port in src.operation.inputs]
+        value = src.operation.evaluate_output(src.index, input_values, results, delays, key_base, bits_override, truncate)
         results[key] = value
         return value