Exception in comparison

[Juan Mauricio Matera]

Description

Wo["x"]>0 raises an exception:

File "mathics-core/mathics/builtin/testing_expressions/equality_inequality.py", line 94, in eval
    c = do_cmp(x, y)
  File "mathics-core/mathics/eval/testing_expressions.py", line 32, in do_cmp
    if s1.is_Float and s2.is_Float:
AttributeError: 'NoneType' object has no attribute 'is_Float'

This seems to happen only if one of the arguments is a String. For example,

• Wo[3]>0
• Wo[f[x]]>0

stays unevaluated, but

• Wo[3, "x"]>0
• Wo[f["x"]]>0

raise the exception.