diff --git a/.gitignore b/.gitignore
index ea8c4bf..1c589f7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,3 @@
 /target
+flamegraph.svg
+perf.data
diff --git a/examples/mandelbrot.puyo b/examples/mandelbrot.puyo
index e291c9a..c52749e 100644
--- a/examples/mandelbrot.puyo
+++ b/examples/mandelbrot.puyo
@@ -45,11 +45,11 @@ ymin ->y0
           (64 iter + put)
         ite
         
-        x0 0.03 + ->x0
+        x0 0.0055 + ->x0
       )
     while!
     10 put
-    y0 0.08 + ->y0
+    y0 0.021 + ->y0
     xmin ->x0
   )
 while!
diff --git a/src/eval.rs b/src/eval.rs
index ab776d1..459104d 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -45,11 +45,11 @@ impl<'a> Val<'a> {
         }
     }
 
-    fn call(&self, stack: &mut Stack<'a>) {
+    fn call(&self, stack: &mut Stack<'a>, out: &mut impl io::Write) {
         match self {
             Val::Num(n) => stack.push(Val::Num(*n)),
             Val::Fun { insts, env } => {
-                eval(insts, stack, &env.clone());
+                eval(insts, stack, &env.clone(), out);
             }
         }
     }
@@ -184,7 +184,12 @@ impl<'a> Stack<'a> {
     }
 }
 
-fn eval<'a>(insts: &'a [Inst<'a>], stack: &mut Stack<'a>, env: &Rc<RefCell<Env<'a>>>) {
+fn eval<'a>(
+    insts: &'a [Inst<'a>],
+    stack: &mut Stack<'a>,
+    env: &Rc<RefCell<Env<'a>>>,
+    out: &mut impl io::Write,
+) {
     for i in insts {
         match i {
             Inst::Set(var) => env.borrow_mut().set(var, stack.pop_default()),
@@ -216,15 +221,15 @@ fn eval<'a>(insts: &'a [Inst<'a>], stack: &mut Stack<'a>, env: &Rc<RefCell<Env<'
                     stack.push(b);
                 }
                 "print" => {
-                    print!("{}", stack.pop_default());
+                    write!(out, "{}", stack.pop_default()).unwrap();
                 }
                 "println" => {
-                    println!("{}", stack.pop_default());
+                    writeln!(out, "{}", stack.pop_default()).unwrap();
                 }
                 "put" => {
                     #[allow(clippy::cast_sign_loss, clippy::cast_possible_truncation)]
                     let byte = stack.pop_num() as u8;
-                    io::stdout().write_all(&[byte]).unwrap();
+                    out.write_all(&[byte]).unwrap();
                 }
                 "explode" => {
                     eprintln!("I ESPLODED");
@@ -240,9 +245,9 @@ fn eval<'a>(insts: &'a [Inst<'a>], stack: &mut Stack<'a>, env: &Rc<RefCell<Env<'
                     let then = stack.pop_default();
                     let test = stack.pop_default();
                     if test.to_num() == 0.0 {
-                        r#else.call(stack);
+                        r#else.call(stack, out);
                     } else {
-                        then.call(stack);
+                        then.call(stack, out);
                     }
                 }
                 _ => stack.push(
@@ -254,7 +259,7 @@ fn eval<'a>(insts: &'a [Inst<'a>], stack: &mut Stack<'a>, env: &Rc<RefCell<Env<'
             Inst::Num(n) => stack.push(Val::Num(*n)),
             Inst::Call => {
                 let f = stack.pop_default();
-                f.call(stack);
+                f.call(stack, out);
             }
             Inst::Block(insts) => stack.push(Val::Fun {
                 insts,
@@ -267,7 +272,12 @@ fn eval<'a>(insts: &'a [Inst<'a>], stack: &mut Stack<'a>, env: &Rc<RefCell<Env<'
     }
 }
 
-pub fn run(insts: &[Inst<'_>]) {
+pub fn run(insts: &[Inst<'_>], out: &mut impl io::Write) {
     let mut stack = Stack::new();
-    eval(insts, &mut stack, &Rc::new(RefCell::new(Env::default())));
+    eval(
+        insts,
+        &mut stack,
+        &Rc::new(RefCell::new(Env::default())),
+        out,
+    );
 }
diff --git a/src/main.rs b/src/main.rs
index 3b4ae76..6b09c95 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -12,5 +12,5 @@ fn main() {
     let insts = parse(&src);
     eprintln!("{}!", Inst::Block(insts.clone()));
 
-    run(&insts);
+    run(&insts, &mut io::BufWriter::new(io::stdout().lock()));
 }