rhai/examples/repl.rs

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Rust
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use rhai::{Engine, EvalAltResult, Scope, AST};
use std::{
io::{stdin, stdout, Write},
iter,
};
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fn print_error(input: &str, err: EvalAltResult) {
fn padding(pad: &str, len: usize) -> String {
iter::repeat(pad).take(len).collect::<String>()
}
let lines: Vec<_> = input.split("\n").collect();
// Print error
match err.position() {
p if p.is_eof() => {
// EOF
let last = lines[lines.len() - 2];
println!("{}", last);
println!("{}^ {}", padding(" ", last.len() - 1), err);
}
p if p.is_none() => {
// No position
println!("{}", err);
}
p => {
// Specific position
let pos_text = format!(
" (line {}, position {})",
p.line().unwrap(),
p.position().unwrap()
);
println!("{}", lines[p.line().unwrap() - 1]);
println!(
"{}^ {}",
padding(" ", p.position().unwrap() - 1),
err.to_string().replace(&pos_text, "")
);
}
}
}
fn main() {
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let mut engine = Engine::new();
let mut scope = Scope::new();
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let mut input = String::new();
let mut ast: Option<AST> = None;
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loop {
print!("rhai> ");
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stdout().flush().expect("couldn't flush stdout");
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input.clear();
if let Err(err) = stdin().read_line(&mut input) {
println!("input error: {}", err);
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}
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// Implement standard commands
match input.as_str().trim() {
"exit" | "quit" => break, // quit
"ast" => {
// print the last AST
match &ast {
Some(ast) => println!("{:#?}", ast),
None => println!("()"),
}
continue;
}
_ => (),
}
if let Err(err) = engine
.compile(&input)
.map_err(EvalAltResult::ErrorParsing)
.and_then(|r| {
ast = Some(r);
engine.consume_ast_with_scope(&mut scope, true, ast.as_ref().unwrap())
})
{
println!("");
print_error(&input, err);
println!("");
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}
}
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}