add small isl changes

diff --git a/pypol/isl.py b/pypol/isl.py
index 74cc5d3..41716c1 100644 (file)
--- a/pypol/isl.py
+++ b/pypol/isl.py
@@ -1,3 +1,7 @@
+"""
+note: for islpy
+isl format: basic set: ("{[x, y] : x >= 0 and x < 5 and y >= 0 and y < x+4 }")
+"""
 
 import ctypes, ctypes.util
 import math
@@ -6,11 +10,11 @@ import operator
 import re
 import functools
 
+
 from decimal import Decimal
 from fractions import Fraction
 from functools import wraps
 
-
 libisl = ctypes.CDLL(ctypes.util.find_library('isl'))
 
 libisl.isl_printer_get_str.restype = ctypes.c_char_p
@@ -37,8 +41,8 @@ class Context:
     def _as_parameter_(self):
         return self._ic
 
-    def __del__(self):
-        libisl.isl_ctx_free(self)
+    #def __del__(self):
+     #   libisl.isl_ctx_free(self)
 
     def __eq__(self, other):
         if not isinstance(other, Context):
@@ -115,12 +119,20 @@ class Value:
             numerator = libisl.isl_val_read_from_str(context, numerator)
             denominator = str(frac.denominator).encode()
             denominator = libisl.isl_val_read_from_str(context, denominator)
-            self._iv = libisl.isl_val_div(numerator, denominator)
+            self._iv = libisl.isl_val_div(numerator, denominator)    
+        print('in isl')            
         return self
 
+
     @property
     def _as_parameter_(self):
         return self._iv
+    
+    def symbols(self):
+        s = set()
+        for constraint in self.constraints():
+            s.update(constraint.symbols)
+        yield from sorted(s)
 
     def __del__(self):
         libisl.isl_val_free(self)
@@ -135,7 +147,7 @@ class Value:
     @property
     def denominator(self):
         if self._denominator is None:
-            raise ValueError('not a rational number')
+            raise ValueError('not a rational number')        
         return self._denominator
 
     def __bool__(self):