.. Copyright 2024 NWChemEx-Project
..
.. 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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DSL Component
#############

These are notes on designing the DSL component.

- We'll need DSLs for combining wavefunctions, operators, and potentially 
  BraKets and chemical systems.
- This component is an attempt to create a reusable DSL framework. It stops
  shy of evaluating the expression that is created.
- We'll have everything use CRTP to inherit from dsl::Term, that way things
  can just take ``Term<T>`` objects and then parse the graph described by
  the object.
- Note that to get const-ness correct the ops need to be templated (e.g., the
  "reference" type of an op needs to mutable if it wraps a mutable object and
  read-only if it wraps a read-only object). This requires TMP to work out the
  correct type.

- To use the DSL promote an object in your

  .. code-block:: C++

     class OperatorImpl<DerivedType, ...>{
     public:
         template<typename DerivedType2, ...>
         auto operator+(const OperatorImpl<DerivedType2>& rhs) const {
             return dsl::Add<DerivedType, DerivedType2>(*this, rhs);
         }