diff --git a/python/code/wypp/__init__.py b/python/code/wypp/__init__.py
index 4074769..024dd33 100644
--- a/python/code/wypp/__init__.py
+++ b/python/code/wypp/__init__.py
@@ -74,3 +74,6 @@ def record(cls=None, mutable=False, globals={}, locals={}):
 resetTestCount = w.resetTestCount
 deepEq = w.deepEq
 wrapTypecheck = w.wrapTypecheck
+WyppTypeError = w.WyppTypeError
+WyppAttributeError = w.WyppAttributeError
+WyppError = w.WyppError
diff --git a/python/code/wypp/ansi.py b/python/code/wypp/ansi.py
index b260837..8a49e9c 100644
--- a/python/code/wypp/ansi.py
+++ b/python/code/wypp/ansi.py
@@ -1,3 +1,5 @@
+import re
+
 RESET         = "\u001b[0;0m"
 BOLD          = "\u001b[1m"
 REVERSE       = "\u001b[2m"
@@ -30,3 +32,7 @@ def red(s):
 
 def blue(s):
     return color(s, BLUE + BOLD)
+
+_ANSI_ESCAPE_RE = re.compile(r'\u001b\[[0-9;]*m')
+def stripAnsi(s: str) -> str:
+    return _ANSI_ESCAPE_RE.sub('', s)
diff --git a/python/code/wypp/errors.py b/python/code/wypp/errors.py
index 332488c..b8b4996 100644
--- a/python/code/wypp/errors.py
+++ b/python/code/wypp/errors.py
@@ -57,7 +57,6 @@ class WyppTypeError(TypeError, WyppError):
     def __init__(self, msg: str, extraFrames: list[inspect.FrameInfo] = []):
         WyppError.__init__(self, extraFrames)
         self.msg = msg
-        self.add_note(msg)
 
     def __str__(self):
         return f'WyppTypeError: {self.msg}'
@@ -290,7 +289,6 @@ class WyppAttributeError(AttributeError, WyppError):
     def __init__(self, msg: str, extraFrames: list[inspect.FrameInfo] = []):
         WyppError.__init__(self, extraFrames)
         self.msg = msg
-        self.add_note(msg)
 
     @staticmethod
     def unknownAttr(clsName: str, attrName: str) -> WyppAttributeError:
@@ -301,12 +299,9 @@ class TodoError(Exception, WyppError):
     def __init__(self, msg: str, extraFrames: list[inspect.FrameInfo] = []):
         WyppError.__init__(self, extraFrames)
         self.msg = msg
-        self.add_note(msg)
-
 
 class ImpossibleError(Exception, WyppError):
     def __init__(self, msg: str, extraFrames: list[inspect.FrameInfo] = []):
         WyppError.__init__(self, extraFrames)
         self.msg = msg
-        self.add_note(msg)
 
diff --git a/python/code/wypp/replTester.py b/python/code/wypp/replTester.py
index a56b009..6f94813 100644
--- a/python/code/wypp/replTester.py
+++ b/python/code/wypp/replTester.py
@@ -1,5 +1,7 @@
 import sys
 import doctest
+from contextlib import contextmanager
+import ansi
 from myLogging import *
 
 # We use our own DocTestParser to replace exception names in stacktraces
@@ -8,7 +10,9 @@
 def rewriteLines(lines: list[str]):
     """
     Each line has exactly one of the following four kinds:
-    - COMMENT: if it starts with '#' (leading whitespace stripped)
+    - COMMENT: if it starts with '#' but not with '##' (leading whitespace stripped)
+      Rationale: lines starting with '##' are error messages from wypp, lines starting only with
+      '#' are real comments in the file defining the doctest.
     - PROMPT: if it starts with '>>>' (leading whitespace stripped)
     - EMPTY: if it contains only whitespace
     - OUTPUT: otherwise
@@ -22,7 +26,7 @@ def get_line_kind(line: str) -> str:
         stripped = line.lstrip()
         if not stripped:
             return 'EMPTY'
-        elif stripped.startswith('#'):
+        elif stripped.startswith('#') and not stripped.startswith('##'):
             return 'COMMENT'
         elif stripped.startswith('>>>'):
             return 'PROMPT'
@@ -56,7 +60,6 @@ def find_next_non_empty(idx: int) -> tuple[int, str]:
             if prev_kind in ['PROMPT', 'OUTPUT'] and next_kind == 'OUTPUT':
                 lines[i] = '<BLANKLINE>'
 
-
 class MyDocTestParser(doctest.DocTestParser):
     def get_examples(self, string, name='<string>'):
         """
@@ -76,10 +79,25 @@ def get_examples(self, string, name='<string>'):
         x = super().get_examples(string, name)
         return x
 
+class MyOutputChecker(doctest.OutputChecker):
+    def check_output(self, want, got, optionflags):
+        got = ansi.stripAnsi(got)
+        return super().check_output(want, got, optionflags)
+
+@contextmanager
+def patchOutputChecker():
+    _Original = doctest.OutputChecker
+    doctest.OutputChecker = MyOutputChecker
+    try:
+        yield
+    finally:
+        doctest.OutputChecker = _Original
+
 def testRepl(repl: str, defs: dict) -> tuple[int, int]:
     doctestOptions = doctest.NORMALIZE_WHITESPACE | doctest.ELLIPSIS
-    (failures, tests) = doctest.testfile(repl, globs=defs, module_relative=False,
-                                         optionflags=doctestOptions, parser=MyDocTestParser())
+    with patchOutputChecker():
+        (failures, tests) = doctest.testfile(repl, globs=defs, module_relative=False,
+                                             optionflags=doctestOptions, parser=MyDocTestParser())
     if failures == 0:
         if tests == 0:
             print(f'No tests in {repl}')
diff --git a/python/code/wypp/runner.py b/python/code/wypp/runner.py
index f42b3a4..41a9433 100644
--- a/python/code/wypp/runner.py
+++ b/python/code/wypp/runner.py
@@ -65,7 +65,14 @@ def main(globals, argList=None):
             printStderr(f'Unsupported language {args.lang}. Supported: ' + ', '.join(i18n.allLanguages))
             sys.exit(1)
 
-    fileToRun: str = args.file
+    isInteractive = args.interactive
+    version = versionMod.readVersion()
+    fileToRun: str|None = args.file
+    if fileToRun is None:
+        if args.repls:
+            import replTester
+            replTester.testRepls(args.repls, globals)
+        return
     if not os.path.exists(fileToRun):
         printStderr(f'File {fileToRun} does not exist')
         sys.exit(1)
@@ -75,11 +82,6 @@ def main(globals, argList=None):
         fileToRun = os.path.basename(fileToRun)
         debug(f'Changed directory to {d}, fileToRun={fileToRun}')
 
-    isInteractive = args.interactive
-    version = versionMod.readVersion()
-
-    if fileToRun is None:
-        return
 
     if not args.checkRunnable and (not args.quiet or args.verbose):
         printWelcomeString(fileToRun, version, doTypecheck=args.checkTypes)
diff --git a/python/code/wypp/stacktrace.py b/python/code/wypp/stacktrace.py
index fcec06e..231c3ed 100644
--- a/python/code/wypp/stacktrace.py
+++ b/python/code/wypp/stacktrace.py
@@ -2,10 +2,12 @@
 import traceback
 import utils
 import inspect
+import threading
 from typing import Optional, Any
 import os
 import sys
 from collections import deque
+from myLogging import *
 
 def tbToFrameList(tb: types.TracebackType) -> list[types.FrameType]:
     cur = tb
@@ -130,5 +132,12 @@ def getReturnTracker():
     obj = sys.getprofile()
     if isinstance(obj, ReturnTracker):
         return obj
+    elif obj is None:
+        if threading.current_thread() is threading.main_thread():
+            raise ValueError(f'No ReturnTracker set, must use installProfileHook before')
+        else:
+            debug('ReturnTracker not available in threads')
+            return None
     else:
-        raise ValueError(f'No ReturnTracker set, must use installProfileHook before')
+        debug(f'Profiling set to some custom profiler: {obj}')
+        return None
diff --git a/python/code/wypp/typecheck.py b/python/code/wypp/typecheck.py
index b1431d3..c1261fa 100644
--- a/python/code/wypp/typecheck.py
+++ b/python/code/wypp/typecheck.py
@@ -253,7 +253,7 @@ def wrapped(*args, **kwargs) -> T:
             utils._call_with_frames_removed(checkArguments, sig, args, kwargs, info, checkCfg)
             returnTracker = stacktrace.getReturnTracker()
             result = utils._call_with_next_frame_removed(f, *args, **kwargs)
-            ft = returnTracker.getReturnFrameType(0)
+            ft = returnTracker.getReturnFrameType(0) if returnTracker else None
             utils._call_with_frames_removed(
                 checkReturn, sig, ft, result, info, checkCfg
             )
diff --git a/python/code/wypp/writeYourProgram.py b/python/code/wypp/writeYourProgram.py
index 197f269..e617799 100644
--- a/python/code/wypp/writeYourProgram.py
+++ b/python/code/wypp/writeYourProgram.py
@@ -324,3 +324,7 @@ def impossible(msg=None):
 math = moduleMath
 
 wrapTypecheck = typecheck.wrapTypecheck
+
+WyppTypeError = errors.WyppTypeError
+WyppAttributeError = errors.WyppAttributeError
+WyppError = errors.WyppError