feat: adding verbose CLI option

Cargo.toml

@@ -16,6 +16,9 @@ categories = ["command-line-utilities", "development-tools", "compilers", "text-
 log = "0.4.21"
 pretty_env_logger = "0.5.0"
 
+# For CLI argument parsing.
+clap = { version = "4.5.0", features = ["derive"] }
+
 # For custom errors.
 thiserror = "2.0.0"
 

README.md

@@ -18,19 +18,18 @@ Monkey has a C-like syntax, supports **variable bindings**, **prefix** and **inf
 
 ## Content
  * [Usage](#usage)
-   + [Usage - Logging](#usage-logging)
  * [Compiling](#compiling)
  * [Unit Testing](#unit-testing)
  * [Issues/Feature Requests](#issuesfeature-requests)
 
 
 ## Usage
+Run the interpreter via
 
+```sh
+monkey_interpreter 
+```
 
-### Usage - Logging
-The crates `pretty_env_logger` and `log` are used to provide logging.
-The environment variable `RUST_LOG` can be used to set the logging level.
-See [https://crates.io/crates/pretty_env_logger](https://crates.io/crates/pretty_env_logger) for more detailed documentation.
 
 
 ## Compiling

src/cli/mod.rs

@@ -0,0 +1,11 @@
+use clap::Parser;
+
+#[derive(Parser, Debug)]
+#[command(version, about, long_about = None)]
+pub(crate) struct Arguments {
+    #[arg(
+        long,
+        help = "Enable verbose output, respects RUST_LOG environment variable if set."
+    )]
+    pub(crate) verbose: bool,
+}

src/main.rs

@@ -5,18 +5,29 @@ extern crate pretty_env_logger;
 use std::io::{stdin, stdout, Write};
 
 use anyhow::{Context, Result};
+use clap::Parser;
 
+use crate::cli::Arguments;
 use crate::evaluator::Evaluator;
 use crate::lexical_analysis::LexicalAnalysis;
 use crate::syntax_analysis::SyntaxAnalysis;
 
+mod cli;
 mod evaluator;
 mod lexical_analysis;
 mod syntax_analysis;
 
 fn main() {
+    info!("Version {}.", env!("CARGO_PKG_VERSION"));
+    let arguments = Arguments::parse();
+    debug!("The command line arguments provided are {arguments:?}.");
+
+    // Set up logging: if verbose is true and RUST_LOG is not set, default to info level
+    if arguments.verbose && std::env::var("RUST_LOG").is_err() {
+        std::env::set_var("RUST_LOG", "info");
+    }
+
     pretty_env_logger::init();
-    trace!("Version {}.", env!("CARGO_PKG_VERSION"));
     let mut evaluator = crate::evaluator::Evaluator::new();
 
     loop {