Finite State Machine parser

Question

I would like to parse a self-designed file format with a FSM-like parser in C++ (this is a teach-myself-c++-the-hard-way-by-doing-something-big-and-di

Answer 1

If you have nesting scopes, then a Finite State Machine is not the right way to go, and you should look at a Context Free Grammar parser. An LL(1) parser can be written as a set of recursive funcitons, or an LALR(1) parser can be written using a parser generator such as Bison.

If you add a stack to an FSM, then you're getting into pushdown automaton territory. A nondeterministic pushdown automaton is equivalent to a context free grammar (though a deterministic pushdown automaton is strictly less powerful.) LALR(1) parser generators actually generate a deterministic pushdown automaton internally. A good compiler design textbook will cover the exact algorithm by which the pushdown automaton is constructed from the grammar. (In this way, adding a stack isn't "hacky".) This Wikipedia article also describes how to construct the LR(1) pushdown automaton from your grammar, but IMO, the article is not as clear as it could be.

If your scopes nest only finitely deep (i.e. you have the upper, normal and list levels but you don't have nested lists or nested normals), then you can use a FSM without a stack.