diff --git a/alv/builtin.moon b/alv/builtin.moon
index 98b4198..ab3a9a0 100644
--- a/alv/builtin.moon
+++ b/alv/builtin.moon
@@ -296,9 +296,9 @@ print = ValueStream.meta
     tick: =>
       if @inputs.value\metatype! == 'event'
         for msg in *@inputs.value!
-          print msg
+          L\print msg
       else
-        print @inputs.value!
+        L\print @inputs.value!
 
 {
   :doc
diff --git a/alv/copilot.moon b/alv/copilot.moon
index 478cbae..a1dc811 100644
--- a/alv/copilot.moon
+++ b/alv/copilot.moon
@@ -48,21 +48,21 @@ class Copilot
         @root\tick_io!
         @root\tick!
       if not ok
-        print error
+        L\print error
       @registry\end_tick!
 
   eval: =>
     @registry\begin_eval!
     ok, ast = Error.try "parsing '#{@file}'", program\match, slurp @file
     if not (ok and ast)
-      print ast or Error 'syntax', "failed to parse"
+      L\print ast or Error 'syntax', "failed to parse"
       @registry\rollback_eval!
       return
 
     scope = Scope globals
     ok, root = Error.try "evaluating '#{@file}'", ast\eval, scope, @registry
     if not ok
-      print root
+      L\print root
       @registry\rollback_eval!
       return
 
@@ -76,8 +76,10 @@ class Copilot
       return
 
     if @last_modification < modification
+      L.stream = io.stderr
       L\log "#{@file} changed at #{modification}"
       @eval!
+      L.stream = io.stdout
       @last_modification = os.time!
 
 {
diff --git a/alv/logger.moon b/alv/logger.moon
index 973e8b5..26126ac 100644
--- a/alv/logger.moon
+++ b/alv/logger.moon
@@ -37,26 +37,30 @@ class Logger
     else
       error unpack res
 
+  --- the stream to write to.
+  -- @tfield file stream
+
 --- static functions
 -- @section static
 
   --- create a new Logger.
   -- @classmethod
   -- @tparam string level the log-level to log at.
-  new: (level='log') =>
+  -- @tparam file stream the stream to write to.
+  new: (level='log', @stream=io.stdout) =>
     @level = levels[level] or level
     @prefix = ''
 
     for name, level in pairs levels
-      @[name] = (first, ...) =>
+      @[name] = (msg) =>
         return unless @level <= level
 
-        where = debug.traceback '', 2
+        msg = tostring msg
+        @stream\write @prefix, msg, '\n'
         if level == levels.error or @level == levels.debug
-          print @prefix .. first, ...
-          print where
-        else
-          print @prefix .. first, ...
+          where = debug.traceback '', 2
+          @stream\write where, '\n'
+        @stream\flush!
 
     if level == levels.print
       @push = (fn, ...) => fn ...
@@ -74,6 +78,7 @@ class Logger
   -- - `'silent'`
   --
   -- @tparam ?string level the level to initialize the logger at.
+  -- @tparam ?file stream the output stream (stdout).
   @init: (...) ->
     L = Logger ...
 
diff --git a/bin/alv-copilot b/bin/alv-copilot
index 9a0cf40..9f2f113 100755
--- a/bin/alv-copilot
+++ b/bin/alv-copilot
@@ -10,10 +10,9 @@ CONF=$tmpdir/conf
 
 cat > "$CONF" << 'EOF'
 split
+screen -t evaltime sh -c 'tty > "$FIFO"; read done < "$FIFO"; screen -X quit'
 focus
-screen -t evaltime sh -c 'tty > "$FIFO"; read done < "$FIFO"'
-focus
-screen -t runtime sh -c 'read tty < "$FIFO";  "alv" $ARGS 2> "$tty";  echo "[press enter to exit]"; read prompt;  echo done > "$FIFO"'
+screen -t runtime sh -c 'read tty < "$FIFO"; "alv" $ARGS 2> "$tty"; echo "[press enter to exit]"; read prompt; screen -X quit'
 EOF
 
 mkfifo "$FIFO"