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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)?;
}
}
}
}