diff --git a/Cargo.toml b/Cargo.toml
index 3ac595b..8a3c8d1 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "rusty_funge"
-version = "2022.12.3"
+version = "2022.12.4"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
@@ -10,4 +10,5 @@ clap = { version = "4.0.29", features = ["derive"] }
 chrono = "0.4.23"
 cursive = { version = "0.20.0", features = ["termion-backend"] }
 rand = "0.8.5"
-num = "0.4.0"
\ No newline at end of file
+num = "0.4.0"
+anyhow = "1.0.66"
\ No newline at end of file
diff --git a/src/debug.rs b/src/debug.rs
index b99909a..6b26848 100644
--- a/src/debug.rs
+++ b/src/debug.rs
@@ -1,133 +1,314 @@
-use std::cmp::{min, max};
-use std::{error::Error, time::Duration};
 use std::fmt::{Display, Formatter};
 use std::sync::{Arc, Mutex};
-use std::thread::{sleep, spawn};
+use std::thread::{spawn, sleep};
+use std::time::{Duration, Instant};
 use cursive::{Cursive, CursiveExt, Printer, Vec2};
-use cursive::{theme::ColorStyle, view::View};
-use cursive::event::{Event, EventResult};
-use rusty_funge::{Int, Funge};
+use cursive::view::View;
+use cursive::theme::{BorderStyle, ColorStyle, Palette, Theme};
+use cursive::event::{Event, EventResult, Key};
+use rusty_funge::{Int, Funge, join, ord, IO};
+use anyhow::Result;
 
 
-struct FungeMutex<I: Int> {
-    funge: Option<Funge<I>>
+// TODO: Use anyhow::Result
+#[derive(Clone)]
+enum FungeError<I: Int> {
+    Funge(Funge<I>),
+    Error(String)
 }
 
-impl<I: Int> FungeMutex<I> {
+
+struct FungeDebug<I: Int> {
+    funge: Option<FungeError<I>>,
+    history: Vec<Funge<I>>,
+    interval: f64,
+    running: bool,
+    stop_op: Option<I>
+}
+
+impl<I: Int> FungeDebug<I> {
     fn new(funge: Funge<I>) -> Self {
-        Self { funge: Some(funge) }
-    }
-
-    fn step(&mut self) -> Result<bool, Box<dyn Error>> {
-        let mut funge = self.funge.to_owned().ok_or("No funge found")?;
-        if !funge.terminated {
-            funge = funge.step()?;
+        Self {
+            funge: Some(FungeError::Funge(funge)),
+            history: Vec::new(),
+            interval: 0.05,
+            running: false,
+            stop_op: None
         }
-        let terminated = funge.terminated;
-        self.funge = Some(funge);
-        Ok(terminated)
     }
 
-    fn funge_ref(&self) -> Option<&Funge<I>> {
-        self.funge.as_ref()
+    fn step_back(&mut self) {
+        match self.history.pop() {
+            Some(funge) => {
+                self.running = false;
+                self.funge = Some(FungeError::Funge(funge));
+            }
+            None => {}
+        }
+    }
+
+    fn is_terminated(&self) -> bool {
+        match &self.funge {
+            Some(FungeError::Funge(f)) if !f.terminated => false,
+            _ => true
+        }
+    }
+
+    fn step(&mut self) {
+        match self.funge.to_owned() {
+            Some(FungeError::Funge(funge)) if !funge.terminated => {
+                self.history.push(funge.clone());
+                if self.history.len() > 16384 {
+                    self.history.remove(0);
+                }
+                match funge.step() {
+                    Ok(f) => self.funge = Some(FungeError::Funge(f)),
+                    Err(e) => {
+                        self.funge = Some(FungeError::Error(e.to_string()))
+                    }
+                }
+            }
+            Some(f) => self.funge = Some(f),
+            None => {}
+        }
     }
 }
 
-impl<I: Int> Display for FungeMutex<I> {
+impl<I: Int> Display for FungeDebug<I> {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.funge.as_ref().expect("No funge found"))
+        match self.funge.as_ref().expect("No funge found") {
+            FungeError::Funge(funge) => write!(f, "{}", funge),
+            FungeError::Error(e) => write!(f, "{}", e)
+        }
     }
 }
 
 
 pub(crate) struct FungeView<I: Int> {
-    funge: Arc<Mutex<FungeMutex<I>>>
+    funge: Arc<Mutex<FungeDebug<I>>>
 }
 
 impl<I: Int> FungeView<I> {
-    pub (crate) fn new(funge: Funge<I>) -> Result<Self, Box<dyn Error>> {
-        Ok(FungeView { funge: Arc::new(Mutex::new(FungeMutex::new(funge.with_output()?))) } )
+    pub (crate) fn new(funge: Funge<I>, input: Vec<String>) -> Result<Self> {
+        Ok(FungeView { funge: Arc::new(Mutex::new(FungeDebug::new(
+            funge.with_input(IO::new()
+                .with_store(input)
+                .with_input(|store| {
+                    Ok(match store.pop() {
+                        None => String::from("5"),  // TODO: cursive input
+                        Some(s) => s
+                    })
+                })).with_output(IO::new()
+                .with_output(|store, s| {
+                    Ok(store.push(s))
+                })))))
+        })
     }
 
-    fn step(&mut self) -> Result<bool, Box<dyn Error>> {
-        self.funge.lock().unwrap().step()
+    fn step_back(&mut self) {
+        match self.funge.lock() {
+            Ok(mut f) => f.step_back(),
+            Err(_) => {}
+        }
     }
 
-    fn get_mutex(&self) -> Self {
+    fn step(&mut self) {
+        match self.funge.lock() {
+            Ok(mut f) => f.step(),
+            Err(_) => {}
+        }
+    }
+
+    pub fn step_n(&mut self, n: usize) {
+        match self.funge.lock() {
+            Ok(mut funge) => {
+                for _ in 0..n {
+                    funge.step();
+                    if funge.is_terminated() { break }
+                }
+            }
+            Err(_) => {}
+        }
+    }
+
+    fn new_mutex(&self) -> Self {
         Self { funge: Arc::clone(&self.funge) }
     }
 
-    pub(crate) fn debug(self, interval: Option<f64>) -> Result<(), Box<dyn Error>> {
+    fn is_running(&self) -> bool {
+        match self.funge.lock() {
+            Ok(mut funge) => {
+                if funge.is_terminated() | !funge.running { return false }
+                if let Some(op) = funge.stop_op {
+                    match funge.funge.as_ref() {
+                        Some(FungeError::Funge(f)) => {
+                            for pos in f.ips_pos() {
+                                if f.code[&pos] == op {
+                                    funge.stop_op = None;
+                                    funge.running = false;
+                                    return false
+                                }
+                            }
+                        }
+                        Some(FungeError::Error(_)) => {
+                            funge.running = false;
+                            return false
+                        }
+                        None => return false
+                    }
+                }
+                true
+            }
+            Err(_) => false
+        }
+    }
+
+    fn toggle_run(&self) {
+        let running = { self.funge.lock().unwrap().running };
+        match running {
+            true => self.pause(),
+            false => self.run()
+        }
+    }
+
+    fn pause(&self) {
+        self.funge.lock().unwrap().running = false;
+    }
+
+    fn run(&self) {
+        let mut funge_mutex = self.new_mutex();
+        { funge_mutex.funge.lock().unwrap().running = true; }
+        spawn(move || {
+            loop {
+                let instant = Instant::now();
+                funge_mutex.step();
+                let duration = Duration::from_micros(match funge_mutex.funge.lock() {
+                    Ok(f) => (f.interval * 1e6) as u64,
+                    Err(_) => 100000
+                });
+                if !funge_mutex.is_running() {
+                    funge_mutex.funge.lock().unwrap().running = false;
+                    break
+                }
+                let sleep_time = duration - instant.elapsed();
+                if sleep_time.as_secs_f64() > 0f64 { sleep(duration) }
+            }
+        });
+    }
+
+    pub(crate) fn debug(self, interval: Option<f64>) {
         let mut app = Cursive::new();
         match interval {
             None => {}
             Some(interval) => {
-                let duration = Duration::from_micros((interval * 1e6) as u64);
-                let mut funge_mutex = self.get_mutex();
-                app.set_fps(max((1f64 / interval) as u32, 50));
-                spawn(move || {
-                    loop {
-                        sleep(duration);
-                        match funge_mutex.step() {
-                            Ok(terminated) => if terminated { break },
-                            Err(_) => break
-                        }
-                    }
-                });
+                { self.funge.lock().unwrap().interval = interval; }
+                self.toggle_run();
             }
         }
         app.add_layer(self);
-        app.add_global_callback('q', |app| app.quit());
+        app.add_global_callback(Key::Esc, |app| app.quit());
+        app.set_autorefresh(true);
+        app.set_theme(Theme { shadow: false, borders: BorderStyle::None, palette: Palette::default() });
         app.run();
-        Ok(())
     }
 }
 
 impl<I: Int> View for FungeView<I> {
     fn draw(&self, printer: &Printer) {
-        let (text, ips_pos, terminated) = {
-            let lock = self.funge.lock();
-            let funge = lock.as_ref().unwrap().funge_ref().unwrap();
-            (format!("{}", funge), funge.ips_pos(), funge.terminated)
-        };
-        let lines: Vec<&str> = text.lines().collect();
-        for (i, line) in lines.iter().enumerate() {
-            printer.print((0, i), line);
-        }
-        for pos in ips_pos.iter() {
-            if (pos[0] >= 0) & (pos[1] >= 0) {
-                let x = pos[0] as usize;
-                let y = pos[1] as usize + 1;
-                printer.with_color(ColorStyle::highlight(), |printer| printer.print((x, y), &*lines[y].chars().nth(x).unwrap().to_string()));
+        match self.funge.lock().as_ref() {
+            Ok(funge_mutex) => {
+                let hist_len = funge_mutex.history.len();
+                let running = funge_mutex.running;
+                match funge_mutex.funge.as_ref() {
+                    Some(FungeError::Funge(funge)) => {
+                        let text = format!("{}", funge);
+                        let lines: Vec<&str> = text.lines().collect();
+                        for (i, line) in lines.iter().enumerate() {
+                            printer.print((0, i), line);
+                        }
+                        for pos in funge.ips_pos().iter() {
+                            if (pos[0] >= 0) & (pos[1] >= 0) {
+                                let x = pos[0] as usize;
+                                let y = pos[1] as usize + 1;
+                                printer.with_color(ColorStyle::highlight(),
+                                                   |printer| {
+                                                       match lines[y].chars().nth(x) {
+                                                           None => {}
+                                                           Some(l) => printer.print((x, y), &*l.to_string())
+                                                       }
+                                                   });
+                            }
+                        }
+                        let n = lines.len() + 1;
+
+                        let mut text = vec!["esc: quit"];
+                        if hist_len > 0 {
+                            text.push("backspace: back");
+                        }
+                        if running {
+                            text.push("space: pause")
+                        } else {
+                            text.push("space: run")
+                        }
+                        if !funge.terminated {
+                            text.push("enter: step")
+                        }
+                        let interval = format!("interval: {} up/down arrow", funge_mutex.interval);
+                        text.push(&*interval);
+                        printer.print((0, n + 1), &*join(&text, ", "));
+                    }
+                    Some(FungeError::Error(e)) => {
+                        printer.print((0, 0), "Error occured:");
+                        printer.print((0, 1), &*format!("{}", e));
+                        printer.print((0, 3), "esc: quit, backspace: back");
+                    }
+                    None => {}
+                }
             }
+            Err(_) => {}
         }
-        let mut bottom = String::from("Press 'q' to quit");
-        if terminated {
-            bottom.push_str(".");
-        } else {
-            bottom.push_str(", any other key to continue.");
-        }
-        printer.print((0, lines.len() + 1), &*bottom);
     }
 
     fn required_size(&mut self, constraint: Vec2) -> Vec2 {
-        let text = format!("{}", self.funge.lock().as_ref().unwrap());
-        let x = match text.lines().map(|line| line.len()).collect::<Vec<usize>>().iter().max() {
-            None => 0,
-            Some(x) => *x
-        };
-        Vec2::new(min(max(80, x), constraint.x), min(max(25, text.lines().count() + 2), constraint.y))
+        constraint
     }
 
     fn on_event(&mut self, event: Event) -> EventResult {
         match event {
-            Event::Char('q') => EventResult::Ignored,
-            Event::Char(_) => {
-                self.step().ok();
+            Event::Key(Key::Esc) => EventResult::Ignored,
+            Event::Key(Key::Backspace) => {
+                self.step_back();
                 EventResult::Consumed(None)
             }
-            Event::Key(_) => {
-                self.step().ok();
+            Event::Char(' ') => {
+                self.toggle_run();
+                EventResult::Consumed(None)
+            }
+            Event::Key(Key::Enter) => {
+                self.step();
+                EventResult::Consumed(None)
+            }
+            Event::Key(Key::Up) => {
+                let lock = self.funge.lock();
+                let mut funge = lock.unwrap();
+                let interval = funge.interval / 2.0;
+                if interval < 0.01 {
+                    funge.interval = 0.01;
+                } else {
+                    funge.interval = interval;
+                }
+                EventResult::Consumed(None)
+            }
+            Event::Key(Key::Down) => {
+                self.funge.lock().unwrap().interval *= 2.0;
+                EventResult::Consumed(None)
+            }
+            Event::Char(c) => {
+                match ord(c) {
+                    Ok(i) => self.funge.lock().unwrap().stop_op = Some(i),
+                    Err(_) => {}
+                }
+                self.run();
                 EventResult::Consumed(None)
             }
             _ => EventResult::Ignored
diff --git a/src/lib.rs b/src/lib.rs
index d182c40..41f1080 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,10 +1,11 @@
 use std::collections::HashMap;
 use std::{env, fs, fmt, fmt::{Debug, Display, Formatter}};
 use std::ops::{Add, Deref, DerefMut, Index, IndexMut, Sub};
-use std::{error::Error, hash::Hash, path::Path, str::FromStr, io::stdin};
+use std::{hash::Hash, path::Path, str::FromStr, io::stdin};
 use chrono::{offset::Local, {Datelike, Timelike}};
 use rand::Rng;
 use num::{Integer, NumCast};
+use anyhow::{Error, Result};
 
 
 const VERSION: &str = env!("CARGO_PKG_VERSION");
@@ -14,7 +15,7 @@ pub trait Int: Integer + NumCast + FromStr + Hash + Clone + Copy + Sync + Send +
 impl<I: Integer + NumCast + FromStr + Hash + Clone + Copy + Sync + Send + Display + 'static> Int for I {}
 
 
-fn join<T: ToString>(v: &Vec<T>, s: &str) -> String {
+pub fn join<T: ToString>(v: &Vec<T>, s: &str) -> String {
     let mut string = String::new();
     if v.len() > 1 {
         for i in 0..v.len() - 1 {
@@ -28,11 +29,11 @@ fn join<T: ToString>(v: &Vec<T>, s: &str) -> String {
     string
 }
 
-fn cast_int<I: NumCast, J: NumCast>(j: J) -> Result<I, Box<dyn Error>> {
-    Ok(I::from(j).ok_or("Could not convert from primitive")?)
+fn cast_int<I: NumCast, J: NumCast>(j: J) -> Result<I> {
+    Ok(I::from(j).ok_or(Error::msg("Could not convert from primitive"))?)
 }
 
-fn cast_vec_int<I: NumCast, J: NumCast>(j: Vec<J>) -> Result<Vec<I>, Box<dyn Error>> {
+fn cast_vec_int<I: NumCast, J: NumCast>(j: Vec<J>) -> Result<Vec<I>> {
     let mut i = Vec::<I>::new();
     for n in j {
         i.push(cast_int(n)?);
@@ -40,12 +41,11 @@ fn cast_vec_int<I: NumCast, J: NumCast>(j: Vec<J>) -> Result<Vec<I>, Box<dyn Err
     Ok(i)
 }
 
-fn ord<I: NumCast>(c: char) -> Result<I, Box<dyn Error>>
-{
+pub fn ord<I: NumCast>(c: char) -> Result<I> {
     Ok(cast_int::<_, u32>(c.try_into()?)?)
 }
 
-fn chr<I: NumCast>(i: I) -> Result<char, Box<dyn Error>> {
+fn chr<I: NumCast>(i: I) -> Result<char> {
     Ok(cast_int::<u32, _>(i)?.try_into()?)
 }
 
@@ -61,51 +61,64 @@ fn sub<I: Sub + Copy>(a: &Vec<I>, b: &Vec<I>) -> Vec<I> where
 
 
 #[derive(Clone)]
-enum InputEnum {
-    StdIn,
-    Vector(Vec<String>)
+pub struct IO {
+    store: Vec<String>,
+    input: fn(&mut Vec<String>) -> Result<String>,
+    output: fn(&mut Vec<String>, String) -> Result<()>
 }
 
-#[derive(Clone)]
-struct Input {
-    source: InputEnum
-}
-
-impl Input {
-    fn get(&mut self) -> Result<String, Box<dyn Error>> {
-        Ok(match self.source {
-            InputEnum::StdIn => {
-                let mut s = String::new();
-                stdin().read_line(&mut s)?;
-                s
+impl IO {
+    pub fn new() -> Self {
+        Self {
+            store: Vec::new(),
+            input: |store| {
+                Ok(match store.pop() {
+                    None => {
+                        let mut s = String::new();
+                        stdin().read_line(&mut s)?;
+                        s
+                    }
+                    Some(s) => s
+                })
+            },
+            output: |_, s| {
+                print!("{}", s);
+                Ok(())
             }
-            InputEnum::Vector(ref mut v) => v.pop().ok_or("No more input!")?
-        })
-    }
-}
-
-
-#[derive(Clone)]
-enum OutputEnum {
-    StdOut,
-    Vector(Vec<String>)
-}
-
-#[derive(Clone)]
-struct Output {
-    sink: OutputEnum
-}
-
-impl Output {
-    fn print(&mut self, string: String) {
-        match self.sink {
-            OutputEnum::StdOut => print!("{}", string),
-            OutputEnum::Vector(ref mut v) => v.push(string)
         }
     }
+
+    pub fn with_store(mut self, mut store: Vec<String>) -> Self {
+        store.reverse();
+        self.store = store;
+        self
+    }
+
+    pub fn with_input(mut self, fun: fn(&mut Vec<String>) -> Result<String>) -> Self {
+        self.input = fun;
+        self
+    }
+
+    pub fn with_output(mut self, fun: fn(&mut Vec<String>, String) -> Result<()>) -> Self {
+        self.output = fun;
+        self
+    }
+
+    fn pop(&mut self) -> Result<String> {
+        (self.input)(&mut self.store)
+    }
+
+    fn push(&mut self, s: String) -> Result<()> {
+        (self.output)(&mut self.store, s)
+    }
+
+    pub fn get(&self) -> String {
+        join(&self.store, "")
+    }
 }
 
 
+
 #[derive(Clone)]
 struct Stack<I: Int> {
     stack: Vec<I>
@@ -229,11 +242,11 @@ impl<I: Int> Display for StackStack<I> {
 
 
 #[derive(Clone)]
-struct IP<I: Int> {
+pub struct IP<I: Int> {  // TODO, getter fns in funge instead of pubs
     id: usize,
     position: Vec<isize>,
     delta: Vec<isize>,
-    offset: Vec<isize>,
+    pub offset: Vec<isize>,
     string: bool,
     stack: StackStack<I>,
     fingerprint_ops: HashMap<I, ()>,
@@ -241,7 +254,7 @@ struct IP<I: Int> {
 
 
 impl<I: Int> IP<I> {
-    fn new(funge: &Funge<I>) -> Result<Self, Box<dyn Error>> {
+    fn new(funge: &Funge<I>) -> Result<Self> {
         let mut new = IP {
             id: funge.ips.len(),
             position: vec![0, 0],
@@ -285,7 +298,7 @@ impl<I: Int> IP<I> {
         self.delta = vec![self.delta[1], -self.delta[0]];
     }
 
-    fn advance(&mut self, funge: &Funge<I>) -> Result<(), Box<dyn Error>> {
+    fn advance(&mut self, funge: &Funge<I>) -> Result<()> {
         let space: I = cast_int(32)?;
         let semicolon: I = cast_int(59)?;
         Ok(if self.string {
@@ -322,7 +335,7 @@ impl<I: Int> IP<I> {
         self.position = self.next_pos(funge);
     }
 
-    fn skip(mut self, funge: Funge<I>) -> Result<(Funge<I>, Option<Vec<Self>>), Box<dyn Error>> {
+    fn skip(mut self, funge: Funge<I>) -> Result<(Funge<I>, Option<Vec<Self>>)> {
         self.movep(&funge);
         if let Ok(32 | 59) = cast_int(self.op(&funge)) {
             self.advance(&funge)?;
@@ -349,7 +362,7 @@ impl<I: Int> IP<I> {
         pos
     }
 
-    fn read_string(&mut self) -> Result<String, Box<dyn Error>> {
+    fn read_string(&mut self) -> Result<String> {
         let mut string = String::new();
         loop {
             let f = self.stack.pop();
@@ -361,7 +374,7 @@ impl<I: Int> IP<I> {
         }
     }
 
-    fn get_info(&self, funge: &Funge<I>, n: I) -> Result<Vec<I>, Box<dyn Error>> {
+    fn get_info(&self, funge: &Funge<I>, n: I) -> Result<Vec<I>> {
         let time = Local::now();
         match n.to_usize() {
             Some(n @ 1..=20) => {
@@ -370,7 +383,7 @@ impl<I: Int> IP<I> {
                     2 => vec![cast_int(8 * std::mem::size_of::<I>())?],
                     3 => {
                         let mut f = 0;
-                        for (i, c) in "wprustyfunge".chars().enumerate() {
+                        for (i, c) in "wprusty".chars().enumerate() {
                             f += (256 as isize).pow(i as u32) * ord::<isize>(c)?;
                         }
                         vec![cast_int(f)?]
@@ -410,8 +423,8 @@ impl<I: Int> IP<I> {
                         r.push(I::zero());
                         let file = &args[0];
                         let path = Path::new(&file);
-                        let j: Vec<I> = path.file_name().ok_or("No file name.")?
-                            .to_str().ok_or("Cannot convert String.")?
+                        let j: Vec<I> = path.file_name().ok_or(Error::msg("No file name."))?
+                            .to_str().ok_or(Error::msg("Cannot convert String."))?
                             .chars().map(|i| ord(i).expect("")).collect();
                         r.extend(j);
                         r.push(I::zero());
@@ -445,21 +458,21 @@ impl<I: Int> IP<I> {
                     }
                 })
             }
-            _ => {
-                // TODO: return Error
-                println!("{}", "Stack size overflow");
-                Ok(Vec::new())
-            }
+            _ => Err(Error::msg("Stack size overflow"))
         }
     }
 
-    fn not_implemented(&mut self, funge: &Funge<I>) {
-        // TODO: reverse or quit option
-        println!("operator {} at {} not implemented", self.op(funge), join(&self.position, ", "));
-        self.reverse()
+    fn not_implemented(mut self, funge: &Funge<I>) -> Option<Self> {
+        match funge.on_error {
+            OnError::Reverse => {
+                self.reverse();
+                Some(self)
+            }
+            OnError::Quit => None
+        }
     }
 
-    fn step(mut self, mut funge: Funge<I>, k: bool) -> Result<(Funge<I>, Option<Vec<Self>>), Box<dyn Error>> {
+    fn step(mut self, mut funge: Funge<I>, k: bool) -> Result<(Funge<I>, Option<Vec<Self>>)> {
         let mut new_ips = Vec::new();
         let op = self.op(&funge);
         let op8 = op.to_u8();
@@ -558,8 +571,8 @@ impl<I: Int> IP<I> {
                     self.stack.push(b);
                 }
                 36 => { self.stack.pop(); } // $
-                46 => funge.output.print(format!("{} ", self.stack.pop())), // .
-                44 => funge.output.print(format!("{}", chr(self.stack.pop())?)), // ,
+                46 => funge.output.push(format!("{} ", self.stack.pop()))?,
+                44 => funge.output.push(format!("{}", chr(self.stack.pop())?))?, // ,
                 35 => { // #
                     self.movep(&funge);
                     return self.skip(funge)
@@ -576,18 +589,18 @@ impl<I: Int> IP<I> {
                     self.stack.push(*&funge.code[&vec![x + self.offset[0], y + self.offset[1]]]);
                 }
                 38 => { // &
-                    let s = funge.inputs.get()?;
+                    let s = funge.input.pop()?;
                     let i: Vec<char> = s.chars()
                         .skip_while(|i| !i.is_digit(10))
                         .take_while(|i| i.is_digit(10)).collect();
                     match join(&i, "").parse() {
                         Ok(n) => self.stack.push(n),
-                        _ => println!("Cannot convert input to number.")  // TODO: Error
+                        _ => Err(Error::msg("Cannot convert input to number."))?
                     }
                 }
                 126 => { // ~
-                    let s = funge.inputs.get()?;
-                    self.stack.push(ord(s.chars().nth(0).ok_or("No valid input.")?)?);
+                    let s = funge.input.pop()?;
+                    self.stack.push(ord(s.chars().nth(0).ok_or(Error::msg("No valid input."))?)?);
                 }
                 64 => { return Ok((funge, Some(Vec::new()))); } // @
                 32 => { // space
@@ -649,7 +662,7 @@ impl<I: Int> IP<I> {
                 }
                 40 => { // ( no fingerprints are implemented
                     // self.read_fingerprint();
-                    // self.fingerprint_ops[] = self.reverse;
+                    // self.fingerprint_ops[] = self.Reverse;
                     self.reverse();
                 }
                 41 => { // )
@@ -670,7 +683,7 @@ impl<I: Int> IP<I> {
                     } else {
                         let text: Vec<&str> = text.lines().collect();
                         let height = text.len();
-                        let width = text.iter().map(|i| i.len()).min().ok_or("Cannot calculate width.")?;
+                        let width = text.iter().map(|i| i.len()).min().ok_or(Error::msg("Cannot calculate width."))?;
                         let mut code: Vec<String> = Vec::new();
                         for line in text {
                             let a = format!("{}{}", line, join(&vec![" "; width - line.len()], ""));
@@ -739,7 +752,10 @@ impl<I: Int> IP<I> {
                     let text = join(&text, "\n");
                     fs::write(file, text)?;
                 }
-                113 => { return Ok((funge, None)) } // q
+                113 => {
+                    funge.return_code = cast_int(self.stack.pop())?;
+                    return Ok((funge, None))
+                } // q
                 114 => self.reverse(), // r
                 115 => { // s
                     self.movep(&funge);
@@ -804,10 +820,16 @@ impl<I: Int> IP<I> {
                 122 => { } // z
                 48..=57 => self.stack.push(self.op(&funge) - cast_int(48)?), // 0123456789
                 97..=102 => self.stack.push(self.op(&funge) - cast_int(87)?), // abcdef
-                _ => self.not_implemented(&funge)
+                _ => self = match self.not_implemented(&funge) {
+                    Some(ip) => ip,
+                    None => return Ok((funge, None))
+                }
             }
         } else {
-            self.not_implemented(&funge);
+            self = match self.not_implemented(&funge) {
+                Some(ip) => ip,
+                None => return Ok((funge, None))
+            }
         }
         if !k {
             self.advance(&funge)?;
@@ -820,7 +842,7 @@ impl<I: Int> IP<I> {
 
 
 #[derive(Clone)]
-struct DefaultHashMap<K: Eq + Hash, V: Clone> {
+pub struct DefaultHashMap<K: Eq + Hash, V: Clone> {
     hashmap: HashMap<K, V>,
     default: V
 }
@@ -854,30 +876,42 @@ impl<K: Eq + Hash, V: Clone> Index<&K> for DefaultHashMap<K, V> {
 }
 
 
+#[derive(Clone)]
+enum OnError {
+    Reverse,
+    #[allow(dead_code)]
+    Quit,
+}
+
+
 #[derive(Clone)]
 pub struct Funge<I: Int> {
-    extent: Vec<isize>,
-    code: DefaultHashMap<Vec<isize>, I>,
-    steps: isize,
-    ips: Vec<IP<I>>,
-    inputs: Input,
-    output: Output,
-    pub terminated: bool
+    pub extent: Vec<isize>,
+    pub code: DefaultHashMap<Vec<isize>, I>,
+    pub steps: isize,
+    pub ips: Vec<IP<I>>,
+    pub input: IO,
+    pub output: IO,
+    pub terminated: bool,
+    pub return_code: i32,
+    on_error: OnError
 }
 
 impl<I: Int> Funge<I> {
-    pub fn new<T: ToString>(code: T) -> Result<Self, Box<dyn Error>> {
+    pub fn new<T: ToString>(code: T) -> Result<Self> {
         let mut new = Self {
             extent: vec![0; 4],
             code: DefaultHashMap::new(cast_int(32)?),
             steps: 0,
             ips: Vec::new(),
-            inputs: Input { source: InputEnum::StdIn },
-            output: Output { sink: OutputEnum::StdOut },
-            terminated: false
+            input: IO::new(),
+            output: IO::new(),
+            terminated: false,
+            return_code: 0,
+            on_error: OnError::Reverse
         };
         let mut code: Vec<String> = code.to_string().lines().map(|i| String::from(i)).collect();
-        let exe = env::current_exe()?.file_name().ok_or("No exe name")?.to_str().unwrap().to_string();
+        let exe = env::current_exe()?.file_name().ok_or(Error::msg("No exe name"))?.to_str().unwrap().to_string();
         if code[0].starts_with(&*format!(r"#!/usr/bin/env {}", exe)) | code[0].starts_with(&*format!(r"#!/usr/bin/env -S {}", exe)) {
             code.remove(0);
         }
@@ -886,25 +920,30 @@ impl<I: Int> Funge<I> {
         Ok(new)
     }
 
-    pub fn from_file(file: &String) -> Result<Self, Box<dyn Error>> {
+    pub fn from_file(file: &String) -> Result<Self> {
         Ok(Self::new(fs::read_to_string(file)?)?)
     }
 
-    pub fn with_inputs(mut self, inputs: Vec<String>) -> Result<Self, Box<dyn Error>> {
-        self.inputs = Input { source: InputEnum::Vector(inputs) };
-        Ok(self)
+    pub fn with_arguments(mut self, args: Vec<String>) -> Self {
+        self.input = IO::new().with_store(args);
+        self
     }
 
-    pub fn with_output(mut self) -> Result<Self, Box<dyn Error>> {
-        self.output = Output { sink: OutputEnum::Vector(Vec::new()) };
-        Ok(self)
+    pub fn with_input(mut self, input: IO) -> Self {
+        self.input = input;
+        self
+    }
+
+    pub fn with_output(mut self, output: IO) -> Self {
+        self.output = output;
+        self
     }
 
     fn insert(&mut self, i: I, x: isize, y: isize) {
         self.code.insert(vec![x, y], i);
     }
 
-    fn insert_code(&mut self, code: Vec<String>, x0: isize, y0: isize) -> Result<(), Box<dyn Error>> {
+    fn insert_code(&mut self, code: Vec<String>, x0: isize, y0: isize) -> Result<()> {
         for (y, line) in code.iter().enumerate() {
             for (x, char) in line.chars().enumerate() {
                 let x1: isize = x.try_into()?;
@@ -926,14 +965,14 @@ impl<I: Int> Funge<I> {
         Ok(())
     }
 
-    pub fn run(mut self) -> Result<Self, Box<dyn Error>>{
+    pub fn run(mut self) -> Result<Self>{
         while !self.terminated {
             self = self.step()?;
         }
         Ok(self)
     }
 
-    pub fn step(mut self) -> Result<Self, Box<dyn Error>> {
+    pub fn step(mut self) -> Result<Self> {
         if !self.terminated {
             self.ips.reverse();
             let mut new_ips = Vec::new();
@@ -998,13 +1037,12 @@ impl<I: Int> Funge<I> {
         string.push_str("\n\nstacks:\n");
         string.push_str(&join(&(&self.ips).iter().map(|ip| ip.stack.to_string()).collect(), "\n"));
 
-        match &self.output.sink {
-            OutputEnum::StdOut => { },
-            OutputEnum::Vector(v) => {
-                string.push_str("\n\nOutput:\n");
-                string.push_str(&join(&v, ""));
-            }
-        };
+        string.push_str("\n\nIP offset:\n");
+        string.push_str(&*join(&self.ips.iter().map(|ip| join(&ip.offset, ", ")).collect(), "; "));
+
+
+        string.push_str("\n\nOutput\n");
+        string.push_str(&self.output.get());
 
         string.push_str("\n\nsteps:\n");
         string.push_str(&self.steps.to_string());
diff --git a/src/main.rs b/src/main.rs
index b2d139b..eb39b8f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,9 +1,9 @@
 mod debug;
 
-use std::error::Error;
 use clap::Parser;
 use rusty_funge::Funge;
 use debug::FungeView;
+use anyhow::Result;
 
 
 #[derive(Parser)]
@@ -16,6 +16,8 @@ struct Args {
     debug: Option<Option<f64>>,
     #[arg(help = "number of bits in cell and funge values", short, long)]
     bits: Option<u8>,
+    #[arg(help = "skip steps", short, long)]
+    steps: Option<usize>,
     #[arg(id = "arguments to the funge (& or ~)")]
     arguments: Vec<String>,
 }
@@ -24,18 +26,24 @@ struct Args {
 macro_rules! run {
     ($a:expr, $i:ty) => {
         let mut funge = Funge::<$i>::from_file(&$a.input)?;
-        if $a.arguments.len() > 0 {
-            funge = funge.with_inputs($a.arguments)?;
-        }
         match $a.debug {
-            Some(interval) => FungeView::new(funge)?.debug(interval).unwrap(),
-            None => { funge.run()?; }
+            Some(interval) => {
+                let mut funge = FungeView::new(funge, $a.arguments)?;
+                if let Some(s) = $a.steps {
+                    funge.step_n(s);
+                }
+                funge.debug(interval);
+            }
+            None => {
+                funge = funge.with_arguments($a.arguments).run()?;
+                std::process::exit(funge.return_code);
+            }
         }
     }
 }
 
 
-fn main() -> Result<(), Box<dyn Error>> {
+fn main() -> Result<()> {
     let args = Args::parse();
     if let None = args.bits {
         run!(args, isize);