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Task/Amb/Python/amb.py

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+import itertools as _itertools
+
+class Amb(object):
+    def __init__(self):
+        self._names2values   = {}       # set of values for each global name
+        self._func           = None     # Boolean constraint function
+        self._valueiterator  = None     # itertools.product of names values
+        self._funcargnames   = None     # Constraint parameter names
+
+    def __call__(self, arg=None):
+        if hasattr(arg, '__code__'):
+            ##
+            ## Called with a constraint function.
+            ##
+            globls = arg.__globals__ if hasattr(arg, '__globals__') else arg.func_globals
+            # Names used in constraint
+            argv = arg.__code__.co_varnames[:arg.__code__.co_argcount]
+            for name in argv:
+                if name not in self._names2values:
+                    assert name in globls, \
+                           "Global name %s not found in function globals" % name
+                    self._names2values[name] = globls[name]
+            # Gather the range of values of all names used in the constraint
+            valuesets = [self._names2values[name] for name in argv]
+            self._valueiterator = _itertools.product(*valuesets)
+            self._func = arg
+            self._funcargnames = argv
+            return self
+        elif arg is not None:
+            ##
+            ## Assume called with an iterable set of values
+            ##
+            arg = frozenset(arg)
+            return arg
+        else:
+            ##
+            ## blank call tries to return next solution
+            ##
+            return self._nextinsearch()
+
+    def _nextinsearch(self):
+        arg = self._func
+        globls = arg.__globals__
+        argv = self._funcargnames
+        found = False
+        for values in self._valueiterator:
+            if arg(*values):
+                # Set globals.
+                found = True
+                for n, v in zip(argv, values):
+                    globls[n] = v
+                break
+        if not found: raise StopIteration
+        return values
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        return self()
+    next = __next__ # Python 2
+
+if __name__ == '__main__':
+    if True:
+        amb = Amb()
+
+        print("\nSmall Pythagorean triples problem:")
+        x = amb(range(1,11))
+        y = amb(range(1,11))
+        z = amb(range(1,11))
+
+        for _dummy in amb( lambda x, y, z: x*x + y*y == z*z ):
+            print ('%s %s %s' % (x, y, z))
+
+
+    if True:
+        amb = Amb()
+
+        print("\nRosetta Code Amb problem:")
+        w1 = amb(["the", "that", "a"])
+        w2 = amb(["frog", "elephant", "thing"])
+        w3 = amb(["walked", "treaded", "grows"])
+        w4 = amb(["slowly", "quickly"])
+
+        for _dummy in amb( lambda w1, w2, w3, w4: \
+                             w1[-1] == w2[0] and \
+                             w2[-1] == w3[0] and \
+                             w3[-1] == w4[0] ):
+            print ('%s %s %s %s' % (w1, w2, w3, w4))
+
+    if True:
+        amb = Amb()
+
+        print("\nAmb problem from "
+            "http://www.randomhacks.net/articles/2005/10/11/amb-operator:")
+        x = amb([1, 2, 3])
+        y = amb([4, 5, 6])
+
+        for _dummy in amb( lambda x, y: x * y != 8 ):
+            print ('%s %s' % (x, y))