ft: restructure with tests

example/hello_world.bf

@@ -0,0 +1 @@
+++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.

src/interpret.rs

@@ -0,0 +1,91 @@
+use std::io::{self, Read};
+
+pub fn interpret(code: &str) -> Vec<u8> {
+    let mut memory = [0 as u8; 10_000];
+    let mut head = 0 as usize;
+    let mut pc = 0 as usize;
+    let mut loop_stack = Vec::new();
+    let mut out = Vec::new();
+
+    let code_bytes = code.as_bytes();
+    while pc < code.len() {
+        match code_bytes[pc] as char {
+            '>' => head += 1,
+            '<' => head -= 1,
+            '+' => memory[head] = memory[head].wrapping_add(1),
+            '-' => memory[head] = memory[head].wrapping_sub(1),
+            '.' => {
+                print!("{}", memory[head] as char);
+                out.push(memory[head]);
+            }
+            ',' => {
+                let mut input_buf = [0u8; 1];
+                if io::stdin().read_exact(&mut input_buf).is_ok() {
+                    memory[head] = input_buf[0];
+                }
+            }
+            '[' => {
+                // loop start
+                if memory[head] == 0 {
+                    let mut count_brackets = 1;
+
+                    // find nested brackets
+                    while count_brackets > 0 {
+                        pc += 1;
+                        if pc >= code_bytes.len() {
+                            panic!("Missing closing loop!");
+                        }
+                        match code_bytes[pc] as char {
+                            // closing current loop
+                            ']' => count_brackets -= 1,
+                            // nested bracket
+                            '[' => count_brackets += 1,
+                            // ignore rest
+                            _ => {}
+                        }
+                    }
+                } else {
+                    // save pc to jump back to
+                    loop_stack.push(pc);
+                }
+            }
+            ']' => {
+                // loop terminator
+                if memory[head] != 0 {
+                    // jump back to loop beginning
+                    if let Some(start_pc) = loop_stack.last() {
+                        pc = *start_pc;
+                    } else {
+                        panic!("Loop stack empty, but still called!")
+                    }
+                } else {
+                    // loop done, continue normally
+                    loop_stack.pop();
+                }
+            }
+            _ => panic!("Invalid instruction"),
+        }
+        pc += 1;
+    }
+    print!("\n");
+    return out;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_h() {
+        let code = "+++++++++[>++++++++<-]>.";
+        let out = interpret(code);
+        assert_eq!(std::str::from_utf8(&out).unwrap(), "H");
+    }
+
+    #[test]
+    fn test_hello() {
+        let code = "++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.";
+        let out = interpret(code);
+        assert_eq!(std::str::from_utf8(&out).unwrap(), "Hello World!\n");
+    }
+}

src/main.rs

@@ -1,73 +1,19 @@
-use std::io::{self, Read};
+use crate::interpret::interpret;
+use std::{env, fs, process};
 
-fn interpret(code: &str) {
+mod interpret;
-    let mut memory = [0 as u8; 10_000];
-    let mut head = 0 as usize;
-    let mut pc = 0 as usize;
-    let mut loop_stack = Vec::new();
-
-    let code_bytes = code.as_bytes();
-    while pc < code.len() {
-        match code_bytes[pc] as char {
-            '>' => head += 1,
-            '<' => head -= 1,
-            '+' => memory[head] = memory[head].wrapping_add(1),
-            '-' => memory[head] = memory[head].wrapping_sub(1),
-            '.' => print!("{}", memory[head] as char),
-            ',' => {
-                let mut input_buf = [0u8; 1];
-                if io::stdin().read_exact(&mut input_buf).is_ok() {
-                    memory[head] = input_buf[0];
-                }
-            }
-            '[' => {
-                // loop start
-                if memory[head] == 0 {
-                    let mut count_brackets = 1;
-
-                    // find nested brackets
-                    while count_brackets > 0 {
-                        pc += 1;
-                        if pc >= code_bytes.len() {
-                            panic!("Missing closing loop!");
-                        }
-                        match code_bytes[pc] as char {
-                            // closing current loop
-                            ']' => count_brackets -= 1,
-                            // nested bracket
-                            '[' => count_brackets += 1,
-                            // ignore rest
-                            _ => {}
-                        }
-                    }
-                } else {
-                    // save pc to jump back to
-                    loop_stack.push(pc);
-                }
-            }
-            ']' => {
-                // loop terminator
-                if memory[head] != 0 {
-                    // jump back to loop beginning
-                    if let Some(start_pc) = loop_stack.last() {
-                        pc = *start_pc;
-                    } else {
-                        panic!("Loop stack empty, but still called!")
-                    }
-                } else {
-                    // loop done, continue normally
-                    loop_stack.pop();
-                }
-            }
-            _ => panic!("Invalid instruction"),
-        }
-        pc += 1;
-    }
-    print!("\n");
-}
 
 fn main() {
-    // let code = "+++++++++[>++++++++<-]>.";
+    let args: Vec<_> = env::args().collect();
-    let code = "++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.";
+    if args.len() != 2 {
-    interpret(code);
+        eprintln!("Usage: {} <filename>", args[0]);
+        process::exit(1);
+    }
+
+    let filename = &args[1];
+    let code = fs::read_to_string(filename).unwrap_or_else(|err| {
+        panic!("Error reading file {}: {}", filename, err);
+    });
+
+    interpret(&code);
 }