peg_calculator.rs - mozsearch

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//! An example of using `peg` with `codespan_reporting`.

//!

//! To run this example, execute the following command from the top level of

//! this repository:

//!

//! ```sh

//! cargo run --example peg_calculator

//! ```

use codespan_reporting::diagnostic::{Diagnostic, Label};

use codespan_reporting::files::SimpleFile;

use codespan_reporting::term;

use codespan_reporting::term::termcolor::{ColorChoice, StandardStream};

use rustyline::error::ReadlineError;

use rustyline::Editor;

peg::parser! {

    grammar arithmetic() for str {

        rule number() -> i64

            = n:$(['0'..='9']+) { n.parse().unwrap() }

        pub rule calculate() -> i64 = precedence!{

            x:(@) "+" y:@ { x + y }

            x:(@) "-" y:@ { x - y }

                  "-" v:@ { - v }

--

            x:(@) "*" y:@ { x * y }

            x:(@) "/" y:@ { x / y }

--

            x:@   "^" y:(@) { i64::pow(x, y as u32) }

            v:@   "!"       { (1..v+1).product() }

--

            "(" v:calculate() ")" { v }

            n:number() { n }

fn main() -> anyhow::Result<()> {

    let writer = StandardStream::stderr(ColorChoice::Always);

    let config = codespan_reporting::term::Config::default();

    let mut editor = Editor::<()>::new();

    loop {

        let line = match editor.readline("> ") {

            Ok(line) => line,

            Err(ReadlineError::Interrupted) | Err(ReadlineError::Eof) => return Ok(()),

            Err(error) => return Err(error.into()),

};

        match arithmetic::calculate(&line) {

            Ok(number) => println!("{}", number),

            Err(error) => {

                let file = SimpleFile::new("<repl>", line);

                let start = error.location.offset;

                let diagnostic = Diagnostic::error()

                    .with_message("parse error")

                    .with_labels(vec![

                        Label::primary((), start..start).with_message("parse error")

])

                    .with_notes(vec![format!("expected: {}", error.expected)]);

                term::emit(&mut writer.lock(), &config, &file, &diagnostic)?;