Rewrite/fix apply() implementation

masque/pattern.py

@@ -14,7 +14,7 @@ import numpy
 from .subpattern import SubPattern
 from .shapes import Shape, Polygon
 from .utils import rotation_matrix_2d, vector2
-
+from .error import PatternError
 
 __author__ = 'Jan Petykiewicz'
 
@@ -105,33 +105,37 @@ class Pattern:
         return pat
 
     def apply(self,
-              func: Callable[['Pattern'], 'Pattern']
+              func: Callable[['Pattern'], 'Pattern'],
+              memo: Dict[int, 'Pattern']=None,
               ) -> 'Pattern':
         """
         Recursively apply func() to this pattern and any pattern it references.
         func() is expected to take and return a Pattern.
-        func() is first applied to the pattern as a whole, then the referenced patterns.
+        func() is first applied to the pattern as a whole, then any referenced patterns.
         It is only applied to any given pattern once, regardless of how many times it is
             referenced.
 
         :param func: Function which accepts a Pattern, and returns a pattern.
+        :param memo: Dictionary used to avoid re-running on multiply-referenced patterns.
+            Stores {id(pattern): func(pattern)} for patterns which have already been processed.
+            Default None (no already-processed patterns).
         :return: The result of applying func() to this pattern and all subpatterns.
         :raises: PatternError if called on a pattern containing a circular reference.
         """
-        pat_map = {id(self): None}
-        pat = func(self)
-        pat_map[id(self)] = pat
+        if memo is None:
+            memo = {}
 
-        for subpat in pat.subpatterns:
-            ref_pat_id = id(subpat.pattern)
-            if ref_pat_id not in pat_map:
-                pat_map[ref_pat_id] = None
-                subpat.pattern = subpat.pattern.apply(func)
-                pat_map[ref_pat_id] = subpat.pattern
-            elif pat_map[ref_pat_id] is None:
-                raise PatternError('.apply() called on pattern with circular reference')
-            else:
-                subpat.pattern = pat_map[ref_pat_id]
+        pat_id = id(self)
+        if pat_id not in memo:
+            memo[pat_id] = None
+            pat = func(self)
+            for subpat in pat.subpatterns:
+                subpat.pattern = subpat.pattern.apply(func, memo)
+            memo[pat_id] = pat
+        elif memo[pat_id] is None:
+            raise PatternError('.apply() called on pattern with circular reference')
+        else:
+            pat = memo[pat_id]
         return pat
 
     def polygonize(self,