Add print & REPL functionality to CLI (#267)

* Add basic REPL functionality
* Add utility function to Realm
* Rework flow to allow files to be loaded as well as open a shell
* Remove shell option (not needed now its the default)
* Update README.md & docs/debugging.md

README.md

@@ -74,6 +74,20 @@ see [CHANGELOG](./CHANGELOG.md)
 - Run with `cargo run -- test.js` where `test.js` is an existing JS file
 - If any JS doesn't work then it's a bug. Please raise an issue!
 
+## Command-line Options
+
+```
+USAGE:
+    boa_cli [FILE]...
+
+FLAGS:
+    -h, --help       Prints help information
+    -V, --version    Prints version information
+
+ARGS:
+    <FILE>...    The JavaScript file(s) to be evaluated
+```
+
 ## Communication
 
 Feel free to contact us on Discord https://discord.gg/tUFFk9Y

boa/src/realm.rs

@@ -5,8 +5,10 @@
 //!A realm is represented in this implementation as a Realm struct with the fields specified from the spec
 use crate::{
     builtins::{
-        array, boolean, console, function, json, math, number, object, regexp, string, symbol,
+        array, boolean, console, function,
-        value::{Value, ValueData},
+        function::NativeFunctionData,
+        json, math, number, object, regexp, string, symbol,
+        value::{ToValue, Value, ValueData},
     },
     environment::{
         declarative_environment_record::DeclarativeEnvironmentRecord,
@@ -65,6 +67,14 @@ impl Realm {
         global.set_field_slice("Symbol", symbol::create_constructor(global));
         global.set_field_slice("console", console::create_constructor(global));
     }
+
+    /// Utility to add a function to the global object
+    pub fn register_global_func(self, func_name: &str, func: NativeFunctionData) -> Self {
+        self.global_obj
+            .set_field(func_name.to_value(), func.to_value());
+
+        self
+    }
 }
 
 // Similar to new_global_environment in lexical_environment, except we need to return a GlobalEnvirionment

boa_cli/src/main.rs

@@ -2,29 +2,27 @@
 #![warn(clippy::perf)]
 #![allow(clippy::cognitive_complexity)]
 
+use boa::builtins::console::log;
 use boa::{exec::Executor, forward_val, realm::Realm};
+use std::io;
 use std::{fs::read_to_string, path::PathBuf};
 use structopt::StructOpt;
-
 /// CLI configuration for Boa.
 #[derive(Debug, StructOpt)]
 #[structopt(author, about)]
 struct Opt {
-    /// The javascript file to be evaluated.
+    /// The JavaScript file(s) to be evaluated.
-    #[structopt(name = "FILE", parse(from_os_str), default_value = "tests/js/test.js")]
+    #[structopt(name = "FILE", parse(from_os_str))]
     files: Vec<PathBuf>,
-    /// Open a boa shell (WIP).
-    #[structopt(short, long)]
-    shell: bool,
 }
-
 pub fn main() -> Result<(), std::io::Error> {
     let args = Opt::from_args();
 
-    let realm = Realm::create();
+    let realm = Realm::create().register_global_func("print", log);
+
     let mut engine = Executor::new(realm);
 
-    for file in args.files {
+    for file in &args.files {
         let buffer = read_to_string(file)?;
 
         match forward_val(&mut engine, &buffer) {
@@ -33,5 +31,18 @@ pub fn main() -> Result<(), std::io::Error> {
         }
     }
 
+    if args.files.is_empty() {
+        loop {
+            let mut buffer = String::new();
+
+            io::stdin().read_line(&mut buffer)?;
+
+            match forward_val(&mut engine, buffer.trim_end()) {
+                Ok(v) => println!("{}", v.to_string()),
+                Err(v) => eprintln!("{}", v.to_string()),
+            }
+        }
+    }
+
     Ok(())
 }

docs/debugging.md

@@ -1,9 +1,10 @@
 # Debugging
 
-There are multiple ways to debug what Boa is doing. Or maybe you just want to know how it works under the hood. Or even test some javaScript.
+There are multiple ways to debug what Boa is doing. Or maybe you just want to know how it works under the hood. Or even test some JavaScript.
 
-The first thing i usually do is add some JS [here](../tests/js/test.js).  
+One way to do so is to create a file in the root of the repository. For example `test.js`. Then execute `cargo run -- test.js` to run the file with boa.
-This file will be read if no arguments are provided. Then boa will begin to parse and execute that JS.
+
+You can also run boa interactively by simply calling `cargo run` without any arguments to start a shell to execute JS.
 
 These are added in order of how the code is read: