Instrument the code.

src/main.rs

@@ -1,26 +1,32 @@
 #![feature(round_char_boundary)]
 use crate::parser::document;
-use tracing::Level;
 use tracing_subscriber::fmt::format::FmtSpan;
-
+use tracing_subscriber::EnvFilter;
 mod parser;
 
 const TEST_DOC: &'static str = include_str!("../toy_language.txt");
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
+    init_telemetry()?;
+    let parsed = document(TEST_DOC);
+    println!("{}\n\n\n", TEST_DOC);
+    println!("{:#?}", parsed);
+    Ok(())
+}
+
+fn init_telemetry() -> Result<(), Box<dyn std::error::Error>> {
+    let env_filter = EnvFilter::try_from_default_env().unwrap_or(EnvFilter::new("WARN"));
     let format = tracing_subscriber::fmt::format()
+        .pretty()
         .with_file(true)
         .with_line_number(true)
         .with_thread_ids(false)
         .with_target(false);
     let subscriber = tracing_subscriber::fmt()
         .event_format(format)
-        .with_max_level(Level::TRACE)
         .with_span_events(FmtSpan::ENTER | FmtSpan::EXIT)
+        .with_env_filter(env_filter)
         .finish();
     tracing::subscriber::set_global_default(subscriber)?;
-    let parsed = document(TEST_DOC);
-    println!("{}\n\n\n", TEST_DOC);
-    println!("{:#?}", parsed);
     Ok(())
 }