Add calc

src/bin/calc.rs

@@ -0,0 +1,70 @@
+use std::fs::File;
+use std::io::{self, BufRead, Read};
+
+use anyhow::Result;
+use clap::Parser;
+
+use cs220::assignments::assignment04::*;
+
+struct Input<'a> {
+    source: Box<dyn BufRead + 'a>,
+}
+
+impl<'a> Input<'a> {
+    fn console(stdin: &'a io::Stdin) -> Input<'a> {
+        Input {
+            source: Box::new(stdin.lock()),
+        }
+    }
+
+    fn file(path: &str) -> io::Result<Input<'a>> {
+        File::open(path).map(|file| Input {
+            source: Box::new(io::BufReader::new(file)),
+        })
+    }
+}
+
+impl<'a> Read for Input<'a> {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        self.source.read(buf)
+    }
+}
+
+impl<'a> BufRead for Input<'a> {
+    fn fill_buf(&mut self) -> io::Result<&[u8]> {
+        self.source.fill_buf()
+    }
+
+    fn consume(&mut self, amt: usize) {
+        self.source.consume(amt);
+    }
+}
+
+#[derive(Parser, Debug)]
+#[clap(author, version, about, long_about = None)]
+struct Args {
+    /// Expression filepath.
+    #[clap(value_parser)]
+    filepath: Option<String>,
+}
+
+fn main() -> Result<()> {
+    // Parses arguments.
+    let args = Args::parse();
+
+    let stdin = io::stdin();
+    let input = if let Some(filepath) = args.filepath {
+        Input::file(&filepath)?
+    } else {
+        Input::console(&stdin)
+    };
+
+    let mut context = context::Context::new();
+    for line in input.lines() {
+        let command = parser::parse_command(&line?)?;
+        let (variable, value) = context.calc_command(&command)?;
+        println!("{} = {}", variable, value);
+    }
+
+    Ok(())
+}