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This file is part of Logtalk <https://logtalk.org/>  
Copyright 1998-2019 Paulo Moura <pmoura@logtalk.org>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
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To load this example and for sample queries, please see the `SCRIPT.txt`
file.

This example illustrates using expected terms to call a conjunction of
goals where any of them may cause an error condition without using the
traditional catch/throw mechanism. This solution allows us to abstract
the error handling code that would be required to test if the previous
goal generated an error before calling the next goal in the conjunction.

The original example is taken from standardization proposals and online
discussions on expected values in the context of other OOP languages such
as C++. For example:

https://blog.tartanllama.xyz/optional-expected/ 

For details please see the comments in the `cascade.lgt` source file.

See also the `expecteds` and `optionals` examples. 
