Introduce a parser for the Walnut language

[dvberkel]

At the moment the Walnut REPL and the expression language are parsed in a brittle way. It is hard to learn the syntax and the semantic of the language when working with the code, they are intertwined.

A more robust, and better maintainable way, is to parse the language with a proper parser.

There are different variant to construct a parser. For example

• Use a parser generator, like ANTLR
• Use a parser combinator, like funcj.parser

In this discussion I would like to tabulate pros and cons for these and other options before making the effort to create a Walnut parser.

[dvberkel]

My preference is with a parser combinator. Among the reasons for this are

• A parser generator has often a different language then the host language which adds to the learning curve.
• There is often a different build step necessary to create the parser code complicating the development cycle

Where parser combinators, allow to express the grammar in code, for which

• the language is the same as the development language
• No additional tools need to be learned