Improve support for functions #2

smnp/error/function.py

@@ -0,0 +1,6 @@
+from smnp.error.base import SmnpException
+
+
+class IllegalFunctionInvocationException(SmnpException):
+    def __init__(self, expected, found):
+        self.msg = f"Illegal function invocation\n\nExpected signature:\n{expected}\n\nFound:\n{found}"