Added convert_to_<type> functions to scalar, and a corresponding cast(x, dtype)

theano/scalar/basic.py

@@ -621,8 +621,6 @@ class Add(ScalarOp):
         else:
           retval += [None]
       return retval
-      #backport
-      #return [(gz if i.type in grad_types else None) for i in inputs]
 add = Add(upcast_out, name = 'add')
 
 class Mul(ScalarOp):
@@ -668,8 +666,6 @@ class Sub(BinaryScalarOp):
           second_part = None
         
         return first_part, second_part
-
-        #return gz if x.type in grad_types else None, -gz if y.type in grad_types else None
 sub = Sub(upcast_out, name = 'sub')
 
 def div_proxy(x, y):
@@ -707,11 +703,7 @@ class TrueDiv(BinaryScalarOp):
           second_part = -(gz * x) / (y * y)
         else:
           second_part = None
-
-        return (first_part, second_part)
-
-        #return (gz / y if x.type in grad_types else None,
-        #        -(gz * x) / (y * y) if y.type in grad_types else None)
+        return first_part, second_part
 true_div = TrueDiv(upcast_out, name = 'true_div')
 
 class IntDiv(BinaryScalarOp):
@@ -825,6 +817,31 @@ class Identity(UnaryScalarOp):
         #return gz if x.type in grad_types else None,
 identity = Identity(same_out, name = 'identity')
 
+#### CASTING OPERATIONS
+
+convert_to_int8 = Identity(specific_out(int8), name='convert_to_int8')
+convert_to_int16 = Identity(specific_out(int16), name='convert_to_int16')
+convert_to_int32 = Identity(specific_out(int32), name='convert_to_int32')
+convert_to_int64 = Identity(specific_out(int64), name='convert_to_int64')
+convert_to_float32 = Identity(specific_out(float32), name='convert_to_float32')
+convert_to_float64 = Identity(specific_out(float64), name='convert_to_float64')
+convert_to_complex64 = Identity(specific_out(complex64), name='convert_to_complex64')
+convert_to_complex128 = Identity(specific_out(complex128), name='convert_to_complex128')
+
+def cast(t, dtype):
+    if t.type.dtype == dtype:
+        return t
+    """symbolically cast `t` to a Scalar of type `dtype`.""" 
+    mapping = {'int8': convert_to_int8,
+               'int16': convert_to_int16,
+               'int32': convert_to_int32,
+               'int64': convert_to_int64,
+               'float32': convert_to_float32,
+               'float64': convert_to_float64,
+               'complex64': convert_to_complex64,
+               'complex128': convert_to_complex128}
+    return mapping[dtype](t)
+
 class Abs(UnaryScalarOp):
     def make_node(self, x):
         inputs = [as_scalar(input) for input in [x]]
@@ -883,8 +900,6 @@ class Neg(UnaryScalarOp):
           return -gz,
         else:
           return None,
-        #backport
-        #return -gz if x.type in grad_types else None,
     def c_code(self, node, name, (x, ), (z, ), sub):
         return "%(z)s = -%(x)s;" % locals()
 neg = Neg(same_out, name = 'neg')