First program: Runs Hello World using PRINT

.gitignore

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+/target

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "basic-interpreter"
+version = "0.1.0"
+dependencies = [
+ "nom",
+]
+
+[[package]]
+name = "memchr"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
+
+[[package]]
+name = "minimal-lexical"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68354c5c6bd36d73ff3feceb05efa59b6acb7626617f4962be322a825e61f79a"
+
+[[package]]
+name = "nom"
+version = "7.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5507769c4919c998e69e49c839d9dc6e693ede4cc4290d6ad8b41d4f09c548c"
+dependencies = [
+ "memchr",
+ "minimal-lexical",
+]

Cargo.toml

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+[package]
+name = "basic-interpreter"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nom = "7.1.2"

inputs/hello_world.bas

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+10 PRINT "Hello, world."

src/basic.rs

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+use nom::{
+    bytes::complete::{tag, take_until},
+    character::complete::u32 as ccu32,
+    combinator::map,
+    sequence::{delimited, terminated, tuple},
+    IResult,
+};
+
+pub type Line<'a> = (u32, Command<'a>);
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum Command<'a> {
+    Print(&'a str),
+    None,
+}
+
+fn read_string(i: &str) -> IResult<&str, &str> {
+    take_until("\"")(i)
+}
+
+fn parse_command(i: &str) -> IResult<&str, Command> {
+    let (i, (command, _)) = tuple((take_until(" "), tag(" ")))(i)?;
+
+    let (i, cmd) = match command {
+        "PRINT" => map(delimited(tag("\""), read_string, tag("\"")), Command::Print)(i)?,
+        _ => (i, Command::None),
+    };
+
+    Ok((i, cmd))
+}
+
+pub fn parse_line(line: &str) -> IResult<&str, Line> {
+    let (i, line_number) = terminated(ccu32, tag(" "))(line)?;
+    let (i, command) = parse_command(i)?;
+    Ok((i, (line_number, command)))
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_parses_a_print_command() {
+        let input = "10 PRINT \"Hello, world\"";
+        let expected = (10, super::Command::Print("Hello, world"));
+
+        let (_, result) = super::parse_line(input).unwrap();
+        assert_eq!(expected, result);
+    }
+}

src/main.rs

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+use std::fs;
+
+mod basic;
+
+fn main() {
+    let file = fs::read_to_string("./inputs/hello_world.bas").unwrap();
+    let lines = file.lines().next().unwrap();
+    let (_, (_, command)) = basic::parse_line(lines).unwrap();
+    match command {
+        basic::Command::Print(input) => {
+            println!("{}", input);
+        }
+        _ => {
+            panic!("Command not recognised");
+        }
+    };
+}