RPN Controller - a generic high level RPN stack machine and languge.

Design Goals

1. Handle parsing, compilation, and execution of RPN/RPL stack based language

2. Only high level stack and application words (direct memory words not implemented)

3. Direct dispatch of native c++ word definition.

4. Extensible with native (c++) words Relatively simple - just add words to the dictionary. Semantics are stil in flux.

5. Extensible with user data types at (c++) compile time Trickier, especially when combined with (#3) above.

Potential designs:

1. Pure Object - The 'stack' is a container of abstract StackObject items. Can be extended by just subclassing 'StackObject'.

Advantages:

• simple for the application designer to implement.
• well established paradigm (java, objective-c, Qt, other frameworks)
• infinitely extensible - add as many subclasses as you need

Disadvantage:

• not clear how the direct dispatch mechanism can properly downcast

2. Pure Variant - The 'stack' is a container of 'std::variant' items. Can be extended by adding to the variant.

Advantages:

• simple to deal with at the parser controller level

Disadvantages:

• Extending by the applicaiton will require changing the core 'std::variant' type.

3. Hybrid - stack uses the variant for 'primitive' types, one of which is 'StackObject' that lets applications subclass and extend.

Disadvantages-

• may not really help the dispatch problem, just pushes it off to the application

4. Codegen - define user words in a way that a codegen can create the intermediates.

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rpn::Stack::Object and friends

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13 Jun - To do

• add unit tests for type words
• implement the rest of the type words
• implement DO/WHILE DO/UNTIL loops
• implement FOR/STEP loops
• finish / test progn compiles
  • nested loops in a word definition
  • nested FOR/DO loops
• implement IF/THEN/ELSE/ENDIF construct
• implement shunting-yard algebraic parser
• implement local variables (??)
• implement STO/RCL memory words
• add StackValidator comparison for early detection of conflicting definitions
• convert UI glossary button(s) to menu items (STACK/MATH/LOGIC/TYPES)
• add UI word to add menus and menu items
• add word to undefine a word