parsing.md

Parsing

Now we combine the parser and the Cargo project, which we generate in the previous two tutorials.

First, we put the two parser files my_grammar.rs and my_grammar_actions.rs into the src directory in the Cargo project.

Second, in the src/main.rs file, we include the two parser files:

mod my_grammar;
mod my_grammar_actions;

Third, we declare our input string and pass it to the parser:

let input = "1 + 2 * 3 + 4";
let result = MyGrammarParser::new().parse(input);

We will print out the result.

The following is the full code:

use my_grammar::MyGrammarParser;
use rustemo::Parser;

mod my_grammar;
mod my_grammar_actions;

fn main() {
    let input = "1 + 2 * 3 + 4";
    let result = MyGrammarParser::new().parse(input);
    
    println!("{:#?}", result);
}

Next, we can run the program:

cargo run

The program outputs the progress of parsing the input. Here is the final part of the output:

Accept
Ok(
    Add(
        Add {
            left: Add(
                Add {
                    left: Number(
                        "1",
                    ),
                    right: Multiply(
                        Multiply {
                            left: Number(
                                "2",
                            ),
                            right: Number(
                                "3",
                            ),
                        },
                    ),
                },
            ),
            right: Number(
                "4",
            ),
        },
    ),
)

We can see that the program transforms the input to a tree structure.

By default, Rustemo parsers skip whitespaces in the input.

➡️ Next: Changing Parser Actions

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