Storing allowed state machine transitions

help
1

I am writing a parser, and I want to allow only certain types of tokens after certain other types of tokens, like, you can't have a number after another number, only a space or an operator. I have a number of different enums, one for each token, and I can create another enum to wrap all of them into one. Or just merge all those separate enums:

enum WhiteSpace {
    WhiteSpace(Vec<char>),
}
pub enum Number {
    Integer(Vec<char>),
    Decimal(Vec<char>),
}
//etc

Instances of each of those enums are fed characters from the input, and when they get a char that does not belong to that type of token, they return an Error. In that case, I want to try and feed that char to every token type that can follow the current one, and for that I need to have some kind of a table, like:

...
WhiteSpace: [Number, Operator],
Number: [WhiteSpace],
Operator: [WhiteSpace]

But how can I do that?

2

Maybe look at the nom crate.

There's a good walk though in this video.

3

Thank you for your reply, but I don't actually need that parser, I am doing this to learn Rust

4

Not sure, but they may have meant that you may find ideas if you look at how nom is implemented.

5

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