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//! Interactive read-eval-print loop.
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//!
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//! Started when `a` is run with no script path. Each line is compiled and run in
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//! the same sandboxed Lua state used for scripts, so the full stdlib (including
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//! the async http/sqlite/os.sleep calls) is available. Evaluation uses the async
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//! executor, matching how files are run.
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use mlua::prelude::{LuaFunction, LuaMultiValue, LuaTable}; |
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use mlua::Lua; |
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use rustyline::error::ReadlineError; |
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use rustyline::DefaultEditor; |
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const PROMPT: &str = "a> "; |
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const CONTINUATION_PROMPT: &str = "..> "; |
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/// Outcome of trying to compile a piece of REPL input.
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enum Compiled { |
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/// A ready-to-run chunk.
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Chunk(LuaFunction), |
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/// Input is syntactically incomplete; more lines are needed.
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Incomplete, |
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/// Input is invalid and cannot become valid by appending more lines.
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Error(mlua::Error), |
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} |
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/// Compile a complete piece of REPL input.
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///
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/// Mirrors stock Lua's `lua.c`: first try the input wrapped in `return ( ... )`
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/// so that bare expressions print their value, and fall back to running it as a
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/// statement. Only the statement form's error decides whether the input is
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/// merely incomplete (so a half-typed expression keeps reading more lines).
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fn compile(lua: &Lua, source: &str) -> Compiled { |
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if let Ok(func) = lua |
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.load(format!("return {source}")) |
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.set_name("=stdin") |
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.into_function() |
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{ |
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return Compiled::Chunk(func); |
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} |
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match lua.load(source).set_name("=stdin").into_function() { |
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Ok(func) => Compiled::Chunk(func), |
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Err(mlua::Error::SyntaxError { |
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incomplete_input: true, |
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.. |
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}) => Compiled::Incomplete, |
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Err(err) => Compiled::Error(err), |
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} |
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} |
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/// Pretty-print the results of an evaluated chunk, one per line, using the
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/// project's own `utils.dump`. Nothing is printed when the chunk returns no
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/// values (e.g. a plain statement).
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fn print_results(lua: &Lua, values: LuaMultiValue) -> mlua::Result<()> { |
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if values.is_empty() { |
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return Ok(()); |
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} |
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let dump: LuaFunction = lua |
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.globals() |
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.get::<LuaTable>("utils")? |
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.get::<LuaFunction>("dump")?; |
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for value in values { |
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let rendered: String = dump.call(value)?; |
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println!("{rendered}"); |
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} |
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Ok(()) |
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} |
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/// Run the interactive REPL against an already-sandboxed Lua state.
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pub(crate) async fn run(lua: &Lua) -> Result<(), Box<dyn std::error::Error>> { |
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let mut editor = DefaultEditor::new()?; |
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let history_path = std::env::var_os("HOME").map(|home| { |
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let mut p = std::path::PathBuf::from(home); |
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p.push(".a_history"); |
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p |
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}); |
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if let Some(path) = &history_path { |
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// A missing history file on first run is not an error.
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let _ = editor.load_history(path); |
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} |
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println!( |
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"a {} — interactive Lua. Ctrl-D to exit.", |
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env!("CARGO_PKG_VERSION") |
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); |
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// Accumulated lines of an as-yet-incomplete statement.
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let mut buffer = String::new(); |
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loop { |
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let prompt = if buffer.is_empty() { |
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PROMPT |
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} else { |
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CONTINUATION_PROMPT |
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}; |
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match editor.readline(prompt) { |
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Ok(line) => { |
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if buffer.is_empty() { |
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buffer = line; |
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} else { |
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buffer.push('\n'); |
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buffer.push_str(&line); |
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} |
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match compile(lua, &buffer) { |
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Compiled::Incomplete => continue, // keep reading continuation lines
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Compiled::Chunk(func) => { |
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let _ = editor.add_history_entry(buffer.as_str()); |
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match func.call_async::<LuaMultiValue>(()).await { |
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Ok(values) => { |
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if let Err(err) = print_results(lua, values) { |
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eprintln!("{err}"); |
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} |
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} |
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Err(err) => eprintln!("{err}"), |
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} |
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buffer.clear(); |
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} |
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Compiled::Error(err) => { |
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let _ = editor.add_history_entry(buffer.as_str()); |
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eprintln!("{err}"); |
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buffer.clear(); |
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} |
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} |
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} |
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// Ctrl-C: abandon the current input and start fresh.
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Err(ReadlineError::Interrupted) => { |
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buffer.clear(); |
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} |
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// Ctrl-D (on an empty line) or end of piped input: quit.
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Err(ReadlineError::Eof) => break, |
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Err(err) => { |
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eprintln!("{err}"); |
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break; |
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} |
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} |
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} |
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if let Some(path) = &history_path { |
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let _ = editor.save_history(path); |
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} |
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Ok(()) |
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} |
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