Separate a kernel for calculations from the REPL logic

[dvberkel]

The entry point of Walnut is the class Main.Prover

Currently the parsing of the walnut expression and the resulting calculation are tightly coupled. Basically the following tight loop is run

1. Try to gobble up the input until a colon (:, or ::) or semi-colon (;).
2. Try to make sense of the collected input, when it is a command
3. Try to make sense of the command and execute it.
4. Return to gobbling up input.

Error handling for all this types is interwoven with the code.

I would like to see a clear separation between the following responsibilities

• Fascilitating a proper Read-Eval-Print Loop (REPL).
• Have proper parser for commands.
• Kernel for calculations.

[jn1z]

For posterity:
Although there is a lot of tight coupling, the crucial main command (def/eval) has a dedicated parser and kernel.

First, a Predicate object is built to make sense of the various operators, variables, etc.
Once the Predicate object is built, it is executed (see EvalComputer), i.e., a kernel.
These are fully separate.