1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
use std::path::PathBuf;
use std::rc::Rc;

use rustc_hash::FxHashMap;
use rustyline::{error::ReadlineError, Editor};
use smol_str::SmolStr;
use tvix_eval::{GlobalsMap, SourceCode, Value};
use tvix_glue::tvix_store_io::TvixStoreIO;

use crate::{
    assignment::Assignment, evaluate, interpret, AllowIncomplete, Args, IncompleteInput,
    InterpretResult,
};

fn state_dir() -> Option<PathBuf> {
    let mut path = dirs::data_dir();
    if let Some(p) = path.as_mut() {
        p.push("tvix")
    }
    path
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) enum ReplCommand<'a> {
    Expr(&'a str),
    Assign(Assignment<'a>),
    Explain(&'a str),
    Print(&'a str),
    Quit,
    Help,
}

impl<'a> ReplCommand<'a> {
    const HELP: &'static str = "
Welcome to the Tvix REPL!

The following commands are supported:

  <expr>       Evaluate a Nix language expression and print the result, along with its inferred type
  <x> = <expr> Bind the result of an expression to a variable
  :d <expr>    Evaluate a Nix language expression and print a detailed description of the result
  :p <expr>    Evaluate a Nix language expression and print the result recursively
  :q           Exit the REPL
  :?, :h       Display this help text
";

    pub fn parse(input: &'a str) -> Self {
        if input.starts_with(':') {
            if let Some(without_prefix) = input.strip_prefix(":d ") {
                return Self::Explain(without_prefix);
            } else if let Some(without_prefix) = input.strip_prefix(":p ") {
                return Self::Print(without_prefix);
            }

            let input = input.trim_end();
            match input {
                ":q" => return Self::Quit,
                ":h" | ":?" => return Self::Help,
                _ => {}
            }
        }

        if let Some(assignment) = Assignment::parse(input) {
            return Self::Assign(assignment);
        }

        Self::Expr(input)
    }
}

pub struct CommandResult {
    output: String,
    continue_: bool,
}

impl CommandResult {
    pub fn finalize(self) -> bool {
        print!("{}", self.output);
        self.continue_
    }

    pub fn output(&self) -> &str {
        &self.output
    }
}

pub struct Repl<'a> {
    /// In-progress multiline input, when the input so far doesn't parse as a complete expression
    multiline_input: Option<String>,
    rl: Editor<()>,
    /// Local variables defined at the top-level in the repl
    env: FxHashMap<SmolStr, Value>,

    io_handle: Rc<TvixStoreIO>,
    args: &'a Args,
    source_map: SourceCode,
    globals: Option<Rc<GlobalsMap>>,
}

impl<'a> Repl<'a> {
    pub fn new(io_handle: Rc<TvixStoreIO>, args: &'a Args) -> Self {
        let rl = Editor::<()>::new().expect("should be able to launch rustyline");
        Self {
            multiline_input: None,
            rl,
            env: FxHashMap::default(),
            io_handle,
            args,
            source_map: Default::default(),
            globals: None,
        }
    }

    pub fn run(&mut self) {
        if self.args.compile_only {
            eprintln!("warning: `--compile-only` has no effect on REPL usage!");
        }

        let history_path = match state_dir() {
            // Attempt to set up these paths, but do not hard fail if it
            // doesn't work.
            Some(mut path) => {
                let _ = std::fs::create_dir_all(&path);
                path.push("history.txt");
                let _ = self.rl.load_history(&path);
                Some(path)
            }

            None => None,
        };

        loop {
            let prompt = if self.multiline_input.is_some() {
                "         > "
            } else {
                "tvix-repl> "
            };

            let readline = self.rl.readline(prompt);
            match readline {
                Ok(line) => {
                    if !self.send(line).finalize() {
                        break;
                    }
                }
                Err(ReadlineError::Interrupted) | Err(ReadlineError::Eof) => break,

                Err(err) => {
                    eprintln!("error: {}", err);
                    break;
                }
            }
        }

        if let Some(path) = history_path {
            self.rl.save_history(&path).unwrap();
        }
    }

    /// Send a line of user input to the REPL. Returns a result indicating the output to show to the
    /// user, and whether or not to continue
    pub fn send(&mut self, line: String) -> CommandResult {
        if line.is_empty() {
            return CommandResult {
                output: String::new(),
                continue_: true,
            };
        }

        let input = if let Some(mi) = &mut self.multiline_input {
            mi.push('\n');
            mi.push_str(&line);
            mi
        } else {
            &line
        };

        let res = match ReplCommand::parse(input) {
            ReplCommand::Quit => {
                return CommandResult {
                    output: String::new(),
                    continue_: false,
                };
            }
            ReplCommand::Help => {
                println!("{}", ReplCommand::HELP);
                Ok(InterpretResult::empty_success(None))
            }
            ReplCommand::Expr(input) => interpret(
                Rc::clone(&self.io_handle),
                input,
                None,
                self.args,
                false,
                AllowIncomplete::Allow,
                Some(&self.env),
                self.globals.clone(),
                Some(self.source_map.clone()),
            ),
            ReplCommand::Assign(Assignment { ident, value }) => {
                match evaluate(
                    Rc::clone(&self.io_handle),
                    &value.to_string(), /* FIXME: don't re-parse */
                    None,
                    self.args,
                    AllowIncomplete::Allow,
                    Some(&self.env),
                    self.globals.clone(),
                    Some(self.source_map.clone()),
                ) {
                    Ok(result) => {
                        if let Some(value) = result.value {
                            self.env.insert(ident.into(), value);
                        }
                        Ok(InterpretResult::empty_success(Some(result.globals)))
                    }
                    Err(incomplete) => Err(incomplete),
                }
            }
            ReplCommand::Explain(input) => interpret(
                Rc::clone(&self.io_handle),
                input,
                None,
                self.args,
                true,
                AllowIncomplete::Allow,
                Some(&self.env),
                self.globals.clone(),
                Some(self.source_map.clone()),
            ),
            ReplCommand::Print(input) => interpret(
                Rc::clone(&self.io_handle),
                input,
                None,
                &Args {
                    strict: true,
                    ..(self.args.clone())
                },
                false,
                AllowIncomplete::Allow,
                Some(&self.env),
                self.globals.clone(),
                Some(self.source_map.clone()),
            ),
        };

        match res {
            Ok(InterpretResult {
                output,
                globals,
                success: _,
            }) => {
                self.rl.add_history_entry(input);
                self.multiline_input = None;
                if globals.is_some() {
                    self.globals = globals;
                }
                CommandResult {
                    output,
                    continue_: true,
                }
            }
            Err(IncompleteInput) => {
                if self.multiline_input.is_none() {
                    self.multiline_input = Some(line);
                }
                CommandResult {
                    output: String::new(),
                    continue_: true,
                }
            }
        }
    }
}