started cli

Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "bng"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+anyhow = "1.0"
+clap = { version = "4.5", features = ["derive"] }
+fasteval = "0.2.4"
+tinyaudio = { version = "0.1", optional = true }
+
+[features]
+default = ["play", "save"]
+play = ["dep:tinyaudio"]
+save = []

src/cli.rs

@@ -0,0 +1,39 @@
+use std::{fs::read_to_string, ops::Deref, path::Path, str::FromStr};
+
+use anyhow::{Context, Error};
+use clap::Parser;
+
+#[derive(Parser)]
+pub(super) struct Args {
+    #[arg(short, long, value_parser = Instrument::from_str)]
+    instrument: Instrument,
+}
+
+impl Args {
+    pub(super) fn instrument(&self) -> &<Instrument as Deref>::Target {
+        &self.instrument
+    }
+}
+
+#[derive(Clone)]
+pub(super) struct Instrument(String);
+
+impl FromStr for Instrument {
+    type Err = Error;
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        let maybe_a_path = Path::new(&value);
+        Ok(Instrument(if maybe_a_path.is_file() {
+            read_to_string(maybe_a_path)
+                .context("you gave me the path of a real file but reading it is hard!")?
+        } else {
+            value.to_owned() // hope it's good
+        }))
+    }
+}
+
+impl Deref for Instrument {
+    type Target = <String as Deref>::Target;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}

src/main.rs

@@ -0,0 +1,10 @@
+use anyhow::Result;
+use clap::Parser;
+
+mod cli;
+
+fn main() -> Result<()> {
+    let args = cli::Args::try_parse()?;
+    println!("got: {}", args.instrument());
+    Ok(())
+}