From 1d3f4a982afc25852d3cc2c639305ce88ed762ad Mon Sep 17 00:00:00 2001
From: Andreas Kloeckner <kloeckner@haamster.rice.edu>
Date: Sun, 16 Nov 2008 13:03:17 -0600
Subject: [PATCH] Add SimplifyingSortingStringifyMapper.

---
 src/mapper/stringifier.py | 63 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/src/mapper/stringifier.py b/src/mapper/stringifier.py
index a80a26b..861f101 100644
--- a/src/mapper/stringifier.py
+++ b/src/mapper/stringifier.py
@@ -131,3 +131,66 @@ class StringifyMapper(pymbolic.mapper.RecursiveMapper):
 
     def map_numpy_array(self, expr, enclosing_prec):
         return 'array(%s)' % str(expr)
+
+
+
+
+class SimplifyingSortingStringifyMapper(StringifyMapper):
+    def map_sum(self, expr, enclosing_prec):
+        entries = [self.rec(i, PREC_SUM) for i in expr.children]
+
+        def get_neg_product(expr):
+            from pymbolic.primitives import is_zero, Product
+
+            if isinstance(expr, Product) \
+                    and len(expr.children) and is_zero(expr.children[0]+1):
+                return Product(expr.children[1:])
+            else:
+                return None
+
+        positives = []
+        negatives = []
+
+        for ch in expr.children:
+            neg_prod = get_neg_product(ch)
+            if neg_prod is not None:
+                negatives.append(self.rec(neg_prod, PREC_SUM))
+            else:
+                positives.append(self.rec(ch, PREC_SUM))
+
+        positives.sort()
+        positives = " + ".join(positives[::-1])
+        negatives.sort()
+        negatives = "".join(" - " + entry for entry in negatives[::-1])
+
+        result = positives + negatives
+
+        if enclosing_prec > PREC_SUM:
+            return "(%s)" % result
+        else:
+            return result
+
+    def map_product(self, expr, enclosing_prec):
+        def generate_entries():
+            i = 0
+            from pymbolic.primitives import is_zero
+
+            while i < len(expr.children):
+                child = expr.children[i]
+                if is_zero(child+1) and i+1 < len(expr.children):
+                    # NOTE: That space needs to be there. 
+                    # Otherwise two unary minus signs merge into a pre-decrement.
+                    yield "- %s" % self.rec(expr.children[i+1], PREC_UNARY)
+                    i += 2
+                else:
+                    yield self.rec(child, PREC_PRODUCT)
+                    i += 1
+
+        entries = list(generate_entries())
+        entries.sort()
+        #entries = entries[::-1]
+
+        if enclosing_prec > PREC_PRODUCT:
+            return "(%s)" % "*".join(entries)
+        else:
+            return "*".join(entries)
-- 
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