From 5ca95271f4d6c17f370e31d758bfd50af9a1fab8 Mon Sep 17 00:00:00 2001
From: Christopher Rink <chrisrink10@gmail.com>
Date: Fri, 26 Jan 2024 16:28:10 -0500
Subject: [PATCH 01/20] Warn at compile time on arity mismatch for function
 invocation

---
 src/basilisp/lang/compiler/analyzer.py | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/basilisp/lang/compiler/analyzer.py b/src/basilisp/lang/compiler/analyzer.py
index 6c5526cf9..917d0672d 100644
--- a/src/basilisp/lang/compiler/analyzer.py
+++ b/src/basilisp/lang/compiler/analyzer.py
@@ -2506,6 +2506,26 @@ def _invoke_ast(form: Union[llist.PersistentList, ISeq], ctx: AnalyzerContext) -
         fn = _analyze_form(form.first, ctx)
 
     if fn.op == NodeOp.VAR and isinstance(fn, VarRef):
+        if ctx.warn_on_arity_mismatch and getattr(fn.var.value, "_basilisp_fn", False):
+            arities: Optional[Tuple[Union[int, kw.Keyword]]] = getattr(
+                fn.var.value, "arities", None
+            )
+            if arities is not None:
+                has_variadic = kw.keyword("rest") in arities
+                fixed_arities = frozenset(
+                    filter(lambda v: v is not kw.keyword("rest"), arities)
+                )
+                # This count could be off by 1 for cases where kwargs are being passed,
+                # but only Basilisp functions intended to be called by Python code
+                # (e.g. with a :kwargs strategy) should ever be called with kwargs,
+                # so this seems unlikely enough.
+                num_args = runtime.count(form.rest)
+                if num_args not in fixed_arities and not has_variadic:
+                    logger.warning(
+                        f"calling function {fn.var} with {num_args} arguments; "
+                        f"expected any of: {', '.join(map(str, arities))}"
+                    )
+
         if _is_macro(fn.var) and ctx.should_macroexpand:
             try:
                 macro_env = ctx.symbol_table.as_env_map()

From 809dced8d85dd635c4ae270d30c942a46cf62cf0 Mon Sep 17 00:00:00 2001
From: Chris Rink <chrisrink10@gmail.com>
Date: Mon, 29 Jan 2024 13:27:39 -0500
Subject: [PATCH 02/20] I guess I'm getting a bunch of random format shit
 thanks black

---
 src/basilisp/lang/compiler/analyzer.py | 20 --------------------
 1 file changed, 20 deletions(-)

diff --git a/src/basilisp/lang/compiler/analyzer.py b/src/basilisp/lang/compiler/analyzer.py
index 917d0672d..6c5526cf9 100644
--- a/src/basilisp/lang/compiler/analyzer.py
+++ b/src/basilisp/lang/compiler/analyzer.py
@@ -2506,26 +2506,6 @@ def _invoke_ast(form: Union[llist.PersistentList, ISeq], ctx: AnalyzerContext) -
         fn = _analyze_form(form.first, ctx)
 
     if fn.op == NodeOp.VAR and isinstance(fn, VarRef):
-        if ctx.warn_on_arity_mismatch and getattr(fn.var.value, "_basilisp_fn", False):
-            arities: Optional[Tuple[Union[int, kw.Keyword]]] = getattr(
-                fn.var.value, "arities", None
-            )
-            if arities is not None:
-                has_variadic = kw.keyword("rest") in arities
-                fixed_arities = frozenset(
-                    filter(lambda v: v is not kw.keyword("rest"), arities)
-                )
-                # This count could be off by 1 for cases where kwargs are being passed,
-                # but only Basilisp functions intended to be called by Python code
-                # (e.g. with a :kwargs strategy) should ever be called with kwargs,
-                # so this seems unlikely enough.
-                num_args = runtime.count(form.rest)
-                if num_args not in fixed_arities and not has_variadic:
-                    logger.warning(
-                        f"calling function {fn.var} with {num_args} arguments; "
-                        f"expected any of: {', '.join(map(str, arities))}"
-                    )
-
         if _is_macro(fn.var) and ctx.should_macroexpand:
             try:
                 macro_env = ctx.symbol_table.as_env_map()

From 12e0a008e9fb0feec204b996c70df55b61164ce6 Mon Sep 17 00:00:00 2001
From: Chris Rink <chrisrink10@gmail.com>
Date: Mon, 29 Jan 2024 13:32:14 -0500
Subject: [PATCH 03/20] More stuff

---
 src/basilisp/lang/seq.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/basilisp/lang/seq.py b/src/basilisp/lang/seq.py
index c41364a3b..ef8aa7521 100644
--- a/src/basilisp/lang/seq.py
+++ b/src/basilisp/lang/seq.py
@@ -259,11 +259,13 @@ def sequence(s: Iterable[T]) -> ISeq[T]:
 
 
 @overload
-def _seq_or_nil(s: None) -> None: ...
+def _seq_or_nil(s: None) -> None:
+    ...
 
 
 @overload
-def _seq_or_nil(s: ISeq) -> Optional[ISeq]: ...
+def _seq_or_nil(s: ISeq) -> Optional[ISeq]:
+    ...
 
 
 def _seq_or_nil(s):

From 3f354a1c46299b35112b7666076dec5eb3d70ae8 Mon Sep 17 00:00:00 2001
From: Christopher Rink <chrisrink10@gmail.com>
Date: Sun, 28 Jan 2024 09:46:28 -0500
Subject: [PATCH 04/20] Ok

---
 src/basilisp/lang/seq.py | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/basilisp/lang/seq.py b/src/basilisp/lang/seq.py
index ef8aa7521..c41364a3b 100644
--- a/src/basilisp/lang/seq.py
+++ b/src/basilisp/lang/seq.py
@@ -259,13 +259,11 @@ def sequence(s: Iterable[T]) -> ISeq[T]:
 
 
 @overload
-def _seq_or_nil(s: None) -> None:
-    ...
+def _seq_or_nil(s: None) -> None: ...
 
 
 @overload
-def _seq_or_nil(s: ISeq) -> Optional[ISeq]:
-    ...
+def _seq_or_nil(s: ISeq) -> Optional[ISeq]: ...
 
 
 def _seq_or_nil(s):

From be52fb564be9a6775624bf49df869113e2a03a5f Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Sun, 11 Feb 2024 10:06:27 -0500
Subject: [PATCH 05/20] Improve compiler exceptions

---
 CHANGELOG.md                            |  1 +
 src/basilisp/cli.py                     |  5 +-
 src/basilisp/lang/compiler/exception.py | 63 ++++++++++++++++-
 src/basilisp/lang/exception.py          | 91 +++++++++++++++++++++++++
 src/basilisp/lang/reader.py             | 47 +++++++++++++
 src/basilisp/prompt.py                  |  3 +-
 6 files changed, 206 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ae3632dd..15c8872e2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  * Added support for `*flush-on-newline*` to flush the `prn` and `println` output stream after the last newline (#865)
  * Added support for binding destructuring in `for` bindings (#774)
  * Added `==` as an alias to `=` (#859)
+ * Added an exception hook and custom exception formatting for `basilisp.lang.compiler.exception.CompilerException` and `basilisp.lang.reader.SyntaxError` to show more useful details to users on errors (#???)
 
 ### Changed
  * Cause exceptions arising from compilation issues during macroexpansion will no longer be nested for each level of macroexpansion (#852)
diff --git a/src/basilisp/cli.py b/src/basilisp/cli.py
index d3da5a69d..d0171736b 100644
--- a/src/basilisp/cli.py
+++ b/src/basilisp/cli.py
@@ -15,6 +15,7 @@
 from basilisp.lang import runtime as runtime
 from basilisp.lang import symbol as sym
 from basilisp.lang import vector as vec
+from basilisp.lang.exception import print_exception
 from basilisp.prompt import get_prompter
 
 CLI_INPUT_FILE_PATH = "<CLI Input>"
@@ -449,11 +450,11 @@ def repl(
                 prompter.print(runtime.lrepr(result))
                 repl_module.mark_repl_result(result)
             except reader.SyntaxError as e:
-                traceback.print_exception(reader.SyntaxError, e, e.__traceback__)
+                print_exception(reader.SyntaxError, e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
             except compiler.CompilerException as e:
-                traceback.print_exception(
+                print_exception(
                     compiler.CompilerException, e, e.__traceback__
                 )
                 repl_module.mark_exception(e)
diff --git a/src/basilisp/lang/compiler/exception.py b/src/basilisp/lang/compiler/exception.py
index 197af52ba..1f5e78b0c 100644
--- a/src/basilisp/lang/compiler/exception.py
+++ b/src/basilisp/lang/compiler/exception.py
@@ -1,9 +1,12 @@
 import ast
+import linecache
 from enum import Enum
-from typing import Any, Dict, Optional, Union
+from types import TracebackType
+from typing import Any, Dict, Optional, Type, Union
 
 import attr
 
+from basilisp.lang.exception import format_exception, format_source_context
 from basilisp.lang import keyword as kw
 from basilisp.lang import map as lmap
 from basilisp.lang.compiler.nodes import Node
@@ -104,3 +107,61 @@ def data(self) -> IPersistentMap:
 
     def __str__(self):
         return f"{self.msg} {lrepr(self.data)}"
+
+
+@format_exception.register(CompilerException)
+def format_compiler_exception(  # pylint: disable=unused-argument
+    e: CompilerException, tp: Type[Exception], tb: TracebackType
+) -> list[str]:
+    """Return context notes for a Compiler Exception"""
+    context_exc: Optional[BaseException] = e.__cause__
+
+    lines = []
+    lines.append("\n")
+    if context_exc is not None:
+        lines.append(f"  exception: {type(context_exc)} from {type(e)}\n")
+    else:
+        lines.append(f"  exception: {type(e)}\n")
+    lines.append(f"      phase: {e.phase.value}\n")
+    if context_exc is None:
+        lines.append(f"    message: {e.msg}\n")
+    elif e.phase in {CompilerPhase.MACROEXPANSION, CompilerPhase.INLINING}:
+        if isinstance(context_exc, CompilerException):
+            lines.append(f"    message: {e.msg}: {context_exc.msg}\n")
+        else:
+            lines.append(f"    message: {e.msg}: {context_exc}\n")
+    else:
+        lines.append(f"    message: {e.msg}: {context_exc}\n")
+    if e.form is not None:
+        lines.append(f"       form: {e.form!r}\n")
+
+    d = e.data
+    line = d.val_at(_LINE)
+    end_line = d.val_at(_END_LINE)
+    if line is not None and end_line is not None and line != end_line:
+        line_nums = f"{line}-{end_line}"
+    elif line is not None:
+        line_nums = str(line)
+    else:
+        line_nums = ""
+
+    if e.filename is not None:
+        lines.append(f"   location: {e.filename}:{line_nums or 'NO_SOURCE_LINE'}\n")
+    elif line_nums:
+        lines.append(f"      lines: {line_nums}\n")
+
+    # Print context source lines around the error. Use the current exception to
+    # derive source lines, but use the inner cause exception to place a marker
+    # around the error.
+    if (
+        e.filename is not None
+        and line is not None
+        and (
+            context_lines := format_source_context(e.filename, line, end_line=end_line)
+        )
+    ):
+        lines.append("    context:\n")
+        lines.append("\n")
+        lines.extend(context_lines)
+
+    return lines
diff --git a/src/basilisp/lang/exception.py b/src/basilisp/lang/exception.py
index 294b5d6d7..e4c77c560 100644
--- a/src/basilisp/lang/exception.py
+++ b/src/basilisp/lang/exception.py
@@ -1,3 +1,10 @@
+import functools
+import linecache
+import os
+import traceback
+from types import TracebackType
+from typing import Optional, Type
+
 import attr
 
 from basilisp.lang.interfaces import IExceptionInfo, IPersistentMap
@@ -16,3 +23,87 @@ def __repr__(self):
 
     def __str__(self):
         return f"{self.message} {lrepr(self.data)}"
+
+
+try:
+    import pygments.lexers
+    import pygments.formatters
+    import pygments.styles
+except ImportError:
+
+    def _format_source(s: str) -> str:
+        return f"{s}\n"
+
+else:
+
+    def _get_formatter_name() -> Optional[str]:
+        if os.environ.get("BASILISP_NO_COLOR", "false").lower() in {"1", "true"}:
+            return None
+        elif os.environ.get("COLORTERM", "") in ("truecolor", "24bit"):
+            return "terminal16m"
+        elif "256" in os.environ.get("TERM", ""):
+            return "terminal256"
+        else:
+            return "terminal"
+
+    def _format_source(s: str) -> str:
+        if (formatter_name := _get_formatter_name()) is not None:
+            return s
+        return pygments.highlight(
+            s,
+            lexer=pygments.lexers.get_lexer_by_name("clojure"),
+            formatter=pygments.formatters.get_formatter_by_name(
+                formatter_name, style=pygments.styles.get_style_by_name("emacs")
+            ),
+        )
+
+
+def format_source_context(
+    filename: str, line: int, end_line: Optional[int] = None, num_context_lines: int = 5
+) -> list[str]:
+    """Format source code context with line numbers and identifiers for the affected
+    line(s)."""
+    assert num_context_lines >= 0
+
+    lines = []
+
+    if not filename.startswith("<") and not filename.endswith(">"):
+        if end_line is not None and end_line != line:
+            cause_range = range(line, end_line + 1)
+        else:
+            cause_range = range(line, line + 1)
+
+        if source_lines := linecache.getlines(filename):
+            start = max(0, line - num_context_lines)
+            end = min((end_line or line) + num_context_lines, len(source_lines))
+            num_justify = max(len(str(start)), len(str(end))) + 1
+            for n, source_line in zip(range(start, end), source_lines[start:end]):
+                if n + 1 in cause_range:
+                    line_marker = " > "
+                else:
+                    line_marker = "   "
+
+                line_num = str(n + 1).rjust(num_justify)
+                lines.append(
+                    f"{line_num}{line_marker}| {_format_source(source_line.rstrip())}"
+                )
+
+    return lines
+
+
+@functools.singledispatch
+def format_exception(e: Exception, tp: Type[Exception], tb: TracebackType) -> list[str]:
+    return traceback.format_exception(tp, e, tb)
+
+
+def print_exception(tp: Type[Exception], e: Exception, tb: TracebackType) -> None:
+    """Print the given exception `e` using Basilisp's own exception formatting.
+
+    For the majority of exception types, this should be identical to the base Python
+    traceback formatting. `basilisp.lang.compiler.CompilerException` and
+    `basilisp.lang.reader.SyntaxError` have special handling to print useful information
+    on exceptions."""
+    print("".join(format_exception(e, tp, tb)))
+
+
+basilisp_excepthook = print_exception
diff --git a/src/basilisp/lang/reader.py b/src/basilisp/lang/reader.py
index e1d27e5af..9f2612edc 100644
--- a/src/basilisp/lang/reader.py
+++ b/src/basilisp/lang/reader.py
@@ -10,6 +10,7 @@
 from datetime import datetime
 from fractions import Fraction
 from itertools import chain
+from types import TracebackType
 from typing import (
     Any,
     Callable,
@@ -24,6 +25,7 @@
     Sequence,
     Set,
     Tuple,
+    Type,
     TypeVar,
     Union,
     cast,
@@ -31,6 +33,7 @@
 
 import attr
 
+from basilisp.lang.exception import format_exception, format_source_context
 from basilisp.lang import keyword as kw
 from basilisp.lang import list as llist
 from basilisp.lang import map as lmap
@@ -152,6 +155,50 @@ def __str__(self):
             return f"{self.message} ({details})"
 
 
+@format_exception.register(SyntaxError)
+def format_syntax_error(
+    e: SyntaxError, tp: Type[Exception], tb: TracebackType
+) -> list[str]:
+    context_exc: Optional[BaseException] = e.__cause__
+
+    lines = []
+    lines.append("\n")
+    if context_exc is not None:
+        lines.append(f"  exception: {type(context_exc)} from {type(e)}\n")
+    else:
+        lines.append(f"  exception: {type(e)}\n")
+    if context_exc is None:
+        lines.append(f"    message: {e.message}\n")
+    else:
+        lines.append(f"    message: {e.message}: {context_exc}\n")
+
+    if e.line is not None and e.col:
+        line_num = f"{e.line}:{e.col}"
+    elif e.line is not None:
+        line_num = str(e.line)
+    else:
+        line_num = ""
+
+    if e.filename is not None:
+        lines.append(f"   location: {e.filename}:{line_num or 'NO_SOURCE_LINE'}\n")
+    elif line_num:
+        lines.append(f"      lines: {line_num}\n")
+
+    # Print context source lines around the error. Use the current exception to
+    # derive source lines, but use the inner cause exception to place a marker
+    # around the error.
+    if (
+        e.filename is not None
+        and e.line is not None
+        and (context_lines := format_source_context(e.filename, e.line))
+    ):
+        lines.append("    context:\n")
+        lines.append("\n")
+        lines.extend(context_lines)
+
+    return lines
+
+
 class UnexpectedEOFError(SyntaxError):
     """Syntax Error type raised when the reader encounters an unexpected EOF
     reading a form.
diff --git a/src/basilisp/prompt.py b/src/basilisp/prompt.py
index 685f31806..3e09dd51c 100644
--- a/src/basilisp/prompt.py
+++ b/src/basilisp/prompt.py
@@ -18,6 +18,7 @@
 
 from basilisp.lang import reader as reader
 from basilisp.lang import runtime as runtime
+from basilisp.lang.exception import print_exception
 
 _USER_DATA_HOME = os.getenv("XDG_DATA_HOME", os.path.expanduser("~/.local/share"))
 BASILISP_USER_DATA = os.path.abspath(os.path.join(_USER_DATA_HOME, "basilisp"))
@@ -103,7 +104,7 @@ def _(event: KeyPressEvent) -> None:
             except reader.SyntaxError as e:
                 run_in_terminal(
                     partial(
-                        traceback.print_exception,
+                        print_exception,
                         reader.SyntaxError,
                         e,
                         e.__traceback__,

From 4fe7f49f708dbbab19a866a493154a5196a16f45 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@Christophers-MacBook-Pro.local>
Date: Tue, 30 Jan 2024 19:31:07 -0500
Subject: [PATCH 06/20] Code formatting

---
 src/basilisp/cli.py                     |  4 +---
 src/basilisp/lang/compiler/exception.py |  2 +-
 src/basilisp/lang/exception.py          | 11 ++++++++---
 src/basilisp/lang/reader.py             |  2 +-
 4 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/src/basilisp/cli.py b/src/basilisp/cli.py
index d0171736b..0f29a3bf9 100644
--- a/src/basilisp/cli.py
+++ b/src/basilisp/cli.py
@@ -454,9 +454,7 @@ def repl(
                 repl_module.mark_exception(e)
                 continue
             except compiler.CompilerException as e:
-                print_exception(
-                    compiler.CompilerException, e, e.__traceback__
-                )
+                print_exception(compiler.CompilerException, e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
             except Exception as e:  # pylint: disable=broad-exception-caught
diff --git a/src/basilisp/lang/compiler/exception.py b/src/basilisp/lang/compiler/exception.py
index 1f5e78b0c..3027484e4 100644
--- a/src/basilisp/lang/compiler/exception.py
+++ b/src/basilisp/lang/compiler/exception.py
@@ -6,10 +6,10 @@
 
 import attr
 
-from basilisp.lang.exception import format_exception, format_source_context
 from basilisp.lang import keyword as kw
 from basilisp.lang import map as lmap
 from basilisp.lang.compiler.nodes import Node
+from basilisp.lang.exception import format_exception, format_source_context
 from basilisp.lang.interfaces import IExceptionInfo, IMeta, IPersistentMap, ISeq
 from basilisp.lang.obj import lrepr
 from basilisp.lang.reader import (
diff --git a/src/basilisp/lang/exception.py b/src/basilisp/lang/exception.py
index e4c77c560..a77bc2691 100644
--- a/src/basilisp/lang/exception.py
+++ b/src/basilisp/lang/exception.py
@@ -26,8 +26,8 @@ def __str__(self):
 
 
 try:
-    import pygments.lexers
     import pygments.formatters
+    import pygments.lexers
     import pygments.styles
 except ImportError:
 
@@ -37,6 +37,10 @@ def _format_source(s: str) -> str:
 else:
 
     def _get_formatter_name() -> Optional[str]:
+        """Get the Pygments formatter name for formatting the source code by
+        inspecting various environment variables set by terminals.
+
+        If `BASILISP_NO_COLOR` is set to a truthy value, use no formatting."""
         if os.environ.get("BASILISP_NO_COLOR", "false").lower() in {"1", "true"}:
             return None
         elif os.environ.get("COLORTERM", "") in ("truecolor", "24bit"):
@@ -47,8 +51,9 @@ def _get_formatter_name() -> Optional[str]:
             return "terminal"
 
     def _format_source(s: str) -> str:
-        if (formatter_name := _get_formatter_name()) is not None:
-            return s
+        """Format source code for terminal output."""
+        if (formatter_name := _get_formatter_name()) is None:
+            return f"{s}\n"
         return pygments.highlight(
             s,
             lexer=pygments.lexers.get_lexer_by_name("clojure"),
diff --git a/src/basilisp/lang/reader.py b/src/basilisp/lang/reader.py
index 9f2612edc..9338da0cb 100644
--- a/src/basilisp/lang/reader.py
+++ b/src/basilisp/lang/reader.py
@@ -33,7 +33,6 @@
 
 import attr
 
-from basilisp.lang.exception import format_exception, format_source_context
 from basilisp.lang import keyword as kw
 from basilisp.lang import list as llist
 from basilisp.lang import map as lmap
@@ -42,6 +41,7 @@
 from basilisp.lang import symbol as sym
 from basilisp.lang import util as langutil
 from basilisp.lang import vector as vec
+from basilisp.lang.exception import format_exception, format_source_context
 from basilisp.lang.interfaces import (
     ILispObject,
     ILookup,

From a794d2cca3134b980316d1c9c16096c80c8250be Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@Christophers-MacBook-Pro.local>
Date: Tue, 30 Jan 2024 20:54:30 -0500
Subject: [PATCH 07/20] Split source formatting into a separate file

---
 src/basilisp/lang/compiler/exception.py |  3 +-
 src/basilisp/lang/exception.py          | 85 ++++---------------------
 src/basilisp/lang/reader.py             |  3 +-
 src/basilisp/lang/source.py             | 82 ++++++++++++++++++++++++
 4 files changed, 97 insertions(+), 76 deletions(-)
 create mode 100644 src/basilisp/lang/source.py

diff --git a/src/basilisp/lang/compiler/exception.py b/src/basilisp/lang/compiler/exception.py
index 3027484e4..d55e53cb9 100644
--- a/src/basilisp/lang/compiler/exception.py
+++ b/src/basilisp/lang/compiler/exception.py
@@ -9,7 +9,7 @@
 from basilisp.lang import keyword as kw
 from basilisp.lang import map as lmap
 from basilisp.lang.compiler.nodes import Node
-from basilisp.lang.exception import format_exception, format_source_context
+from basilisp.lang.exception import format_exception
 from basilisp.lang.interfaces import IExceptionInfo, IMeta, IPersistentMap, ISeq
 from basilisp.lang.obj import lrepr
 from basilisp.lang.reader import (
@@ -18,6 +18,7 @@
     READER_END_LINE_KW,
     READER_LINE_KW,
 )
+from basilisp.lang.source import format_source_context
 from basilisp.lang.typing import LispForm
 
 _FILE = kw.keyword("file")
diff --git a/src/basilisp/lang/exception.py b/src/basilisp/lang/exception.py
index a77bc2691..6147b19a3 100644
--- a/src/basilisp/lang/exception.py
+++ b/src/basilisp/lang/exception.py
@@ -1,6 +1,4 @@
 import functools
-import linecache
-import os
 import traceback
 from types import TracebackType
 from typing import Optional, Type
@@ -25,83 +23,22 @@ def __str__(self):
         return f"{self.message} {lrepr(self.data)}"
 
 
-try:
-    import pygments.formatters
-    import pygments.lexers
-    import pygments.styles
-except ImportError:
-
-    def _format_source(s: str) -> str:
-        return f"{s}\n"
-
-else:
-
-    def _get_formatter_name() -> Optional[str]:
-        """Get the Pygments formatter name for formatting the source code by
-        inspecting various environment variables set by terminals.
-
-        If `BASILISP_NO_COLOR` is set to a truthy value, use no formatting."""
-        if os.environ.get("BASILISP_NO_COLOR", "false").lower() in {"1", "true"}:
-            return None
-        elif os.environ.get("COLORTERM", "") in ("truecolor", "24bit"):
-            return "terminal16m"
-        elif "256" in os.environ.get("TERM", ""):
-            return "terminal256"
-        else:
-            return "terminal"
-
-    def _format_source(s: str) -> str:
-        """Format source code for terminal output."""
-        if (formatter_name := _get_formatter_name()) is None:
-            return f"{s}\n"
-        return pygments.highlight(
-            s,
-            lexer=pygments.lexers.get_lexer_by_name("clojure"),
-            formatter=pygments.formatters.get_formatter_by_name(
-                formatter_name, style=pygments.styles.get_style_by_name("emacs")
-            ),
-        )
-
-
-def format_source_context(
-    filename: str, line: int, end_line: Optional[int] = None, num_context_lines: int = 5
+@functools.singledispatch
+def format_exception(
+    e: Optional[Exception], tp: Optional[Type[Exception]], tb: Optional[TracebackType]
 ) -> list[str]:
-    """Format source code context with line numbers and identifiers for the affected
-    line(s)."""
-    assert num_context_lines >= 0
-
-    lines = []
-
-    if not filename.startswith("<") and not filename.endswith(">"):
-        if end_line is not None and end_line != line:
-            cause_range = range(line, end_line + 1)
-        else:
-            cause_range = range(line, line + 1)
-
-        if source_lines := linecache.getlines(filename):
-            start = max(0, line - num_context_lines)
-            end = min((end_line or line) + num_context_lines, len(source_lines))
-            num_justify = max(len(str(start)), len(str(end))) + 1
-            for n, source_line in zip(range(start, end), source_lines[start:end]):
-                if n + 1 in cause_range:
-                    line_marker = " > "
-                else:
-                    line_marker = "   "
+    """Format an exception into something readable, returning a list of newline
+    terminated strings.
 
-                line_num = str(n + 1).rjust(num_justify)
-                lines.append(
-                    f"{line_num}{line_marker}| {_format_source(source_line.rstrip())}"
-                )
-
-    return lines
-
-
-@functools.singledispatch
-def format_exception(e: Exception, tp: Type[Exception], tb: TracebackType) -> list[str]:
+    For the majority of Python exceptions, this will just be the result from calling
+    `traceback.format_exception`. For Basilisp specific compilation errors, a custom
+    output will be returned."""
     return traceback.format_exception(tp, e, tb)
 
 
-def print_exception(tp: Type[Exception], e: Exception, tb: TracebackType) -> None:
+def print_exception(
+    e: Optional[Exception], tp: Optional[Type[Exception]], tb: Optional[TracebackType]
+) -> None:
     """Print the given exception `e` using Basilisp's own exception formatting.
 
     For the majority of exception types, this should be identical to the base Python
diff --git a/src/basilisp/lang/reader.py b/src/basilisp/lang/reader.py
index 9338da0cb..e27394f6d 100644
--- a/src/basilisp/lang/reader.py
+++ b/src/basilisp/lang/reader.py
@@ -41,7 +41,7 @@
 from basilisp.lang import symbol as sym
 from basilisp.lang import util as langutil
 from basilisp.lang import vector as vec
-from basilisp.lang.exception import format_exception, format_source_context
+from basilisp.lang.exception import format_exception
 from basilisp.lang.interfaces import (
     ILispObject,
     ILookup,
@@ -63,6 +63,7 @@
     get_current_ns,
     lrepr,
 )
+from basilisp.lang.source import format_source_context
 from basilisp.lang.typing import IterableLispForm, LispForm, ReaderForm
 from basilisp.lang.util import munge
 from basilisp.util import Maybe, partition
diff --git a/src/basilisp/lang/source.py b/src/basilisp/lang/source.py
new file mode 100644
index 000000000..c5f6bd857
--- /dev/null
+++ b/src/basilisp/lang/source.py
@@ -0,0 +1,82 @@
+import linecache
+import os
+from typing import Optional
+
+try:
+    import pygments.formatters
+    import pygments.lexers
+    import pygments.styles
+except ImportError:
+
+    def _format_source(s: str) -> str:
+        return f"{s}\n"
+
+else:
+
+    def _get_formatter_name() -> Optional[str]:
+        """Get the Pygments formatter name for formatting the source code by
+        inspecting various environment variables set by terminals.
+
+        If `BASILISP_NO_COLOR` is set to a truthy value, use no formatting."""
+        if os.environ.get("BASILISP_NO_COLOR", "false").lower() in {"1", "true"}:
+            return None
+        elif os.environ.get("COLORTERM", "") in ("truecolor", "24bit"):
+            return "terminal16m"
+        elif "256" in os.environ.get("TERM", ""):
+            return "terminal256"
+        else:
+            return "terminal"
+
+    def _format_source(s: str) -> str:
+        """Format source code for terminal output."""
+        if (formatter_name := _get_formatter_name()) is None:
+            return f"{s}\n"
+        return pygments.highlight(
+            s,
+            lexer=pygments.lexers.get_lexer_by_name("clojure"),
+            formatter=pygments.formatters.get_formatter_by_name(
+                formatter_name, style=pygments.styles.get_style_by_name("emacs")
+            ),
+        )
+
+
+def format_source_context(
+    filename: str,
+    line: int,
+    end_line: Optional[int] = None,
+    num_context_lines: int = 5,
+    show_cause_marker: bool = True,
+) -> list[str]:
+    """Format source code context with line numbers and identifiers for the affected
+    line(s)."""
+    assert num_context_lines >= 0
+
+    lines = []
+
+    if not filename.startswith("<") and not filename.endswith(">"):
+        cause_range: Optional[range]
+        if not show_cause_marker:
+            cause_range = None
+        elif end_line is not None and end_line != line:
+            cause_range = range(line, end_line)
+        else:
+            cause_range = range(line, line)
+
+        if source_lines := linecache.getlines(filename):
+            start = max(0, line - num_context_lines)
+            end = min((end_line or line) + num_context_lines, len(source_lines))
+            num_justify = max(len(str(start)), len(str(end))) + 1
+            for n, source_line in zip(range(start, end), source_lines[start:end]):
+                if cause_range is None:
+                    line_marker = " "
+                elif n + 1 in cause_range:
+                    line_marker = " > "
+                else:
+                    line_marker = "   "
+
+                line_num = str(n + 1).rjust(num_justify)
+                lines.append(
+                    f"{line_num}{line_marker}| {_format_source(source_line.rstrip())}"
+                )
+
+    return lines

From 48517052b651871bcd4779256551f6ce36428e09 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@Christophers-MacBook-Pro.local>
Date: Wed, 31 Jan 2024 08:35:32 -0500
Subject: [PATCH 08/20] Hook it

---
 src/basilisp/cli.py                     |  6 ++-
 src/basilisp/lang/compiler/exception.py |  9 ++--
 src/basilisp/lang/exception.py          |  7 +--
 src/basilisp/lang/reader.py             |  7 ++-
 src/basilisp/lang/runtime.py            | 57 ++++++++++++++++++++++++-
 src/basilisp/lang/source.py             |  4 +-
 src/basilisp/main.py                    |  2 +
 src/basilisp/prompt.py                  |  4 +-
 8 files changed, 74 insertions(+), 22 deletions(-)

diff --git a/src/basilisp/cli.py b/src/basilisp/cli.py
index 0f29a3bf9..cc95efb14 100644
--- a/src/basilisp/cli.py
+++ b/src/basilisp/cli.py
@@ -450,11 +450,13 @@ def repl(
                 prompter.print(runtime.lrepr(result))
                 repl_module.mark_repl_result(result)
             except reader.SyntaxError as e:
-                print_exception(reader.SyntaxError, e, e.__traceback__)
+                runtime.basilisp_except_hook(reader.SyntaxError, e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
             except compiler.CompilerException as e:
-                print_exception(compiler.CompilerException, e, e.__traceback__)
+                runtime.basilisp_except_hook(
+                    compiler.CompilerException, e, e.__traceback__
+                )
                 repl_module.mark_exception(e)
                 continue
             except Exception as e:  # pylint: disable=broad-exception-caught
diff --git a/src/basilisp/lang/compiler/exception.py b/src/basilisp/lang/compiler/exception.py
index d55e53cb9..7ccdafe5a 100644
--- a/src/basilisp/lang/compiler/exception.py
+++ b/src/basilisp/lang/compiler/exception.py
@@ -2,7 +2,7 @@
 import linecache
 from enum import Enum
 from types import TracebackType
-from typing import Any, Dict, Optional, Type, Union
+from typing import Any, Dict, List, Optional, Type, Union
 
 import attr
 
@@ -113,12 +113,11 @@ def __str__(self):
 @format_exception.register(CompilerException)
 def format_compiler_exception(  # pylint: disable=unused-argument
     e: CompilerException, tp: Type[Exception], tb: TracebackType
-) -> list[str]:
-    """Return context notes for a Compiler Exception"""
+) -> List[str]:
+    """Format a compiler exception as a list of newline-terminated strings."""
     context_exc: Optional[BaseException] = e.__cause__
 
-    lines = []
-    lines.append("\n")
+    lines = ["\n"]
     if context_exc is not None:
         lines.append(f"  exception: {type(context_exc)} from {type(e)}\n")
     else:
diff --git a/src/basilisp/lang/exception.py b/src/basilisp/lang/exception.py
index 6147b19a3..e815c4ba7 100644
--- a/src/basilisp/lang/exception.py
+++ b/src/basilisp/lang/exception.py
@@ -1,7 +1,7 @@
 import functools
 import traceback
 from types import TracebackType
-from typing import Optional, Type
+from typing import List, Optional, Type
 
 import attr
 
@@ -26,7 +26,7 @@ def __str__(self):
 @functools.singledispatch
 def format_exception(
     e: Optional[Exception], tp: Optional[Type[Exception]], tb: Optional[TracebackType]
-) -> list[str]:
+) -> List[str]:
     """Format an exception into something readable, returning a list of newline
     terminated strings.
 
@@ -46,6 +46,3 @@ def print_exception(
     `basilisp.lang.reader.SyntaxError` have special handling to print useful information
     on exceptions."""
     print("".join(format_exception(e, tp, tb)))
-
-
-basilisp_excepthook = print_exception
diff --git a/src/basilisp/lang/reader.py b/src/basilisp/lang/reader.py
index e27394f6d..b94e83d2f 100644
--- a/src/basilisp/lang/reader.py
+++ b/src/basilisp/lang/reader.py
@@ -157,13 +157,12 @@ def __str__(self):
 
 
 @format_exception.register(SyntaxError)
-def format_syntax_error(
+def format_syntax_error(  # pylint: disable=unused-argumentma
     e: SyntaxError, tp: Type[Exception], tb: TracebackType
-) -> list[str]:
+) -> List[str]:
     context_exc: Optional[BaseException] = e.__cause__
 
-    lines = []
-    lines.append("\n")
+    lines = ["\n"]
     if context_exc is not None:
         lines.append(f"  exception: {type(context_exc)} from {type(e)}\n")
     else:
diff --git a/src/basilisp/lang/runtime.py b/src/basilisp/lang/runtime.py
index 6ad35a377..bc35a6df6 100644
--- a/src/basilisp/lang/runtime.py
+++ b/src/basilisp/lang/runtime.py
@@ -46,6 +46,7 @@
 from basilisp.lang import symbol as sym
 from basilisp.lang import vector as vec
 from basilisp.lang.atom import Atom
+from basilisp.lang.exception import print_exception
 from basilisp.lang.interfaces import (
     IAssociative,
     IBlockingDeref,
@@ -84,6 +85,8 @@
 COMPILER_OPTIONS_VAR_NAME = "*compiler-options*"
 COMMAND_LINE_ARGS_VAR_NAME = "*command-line-args*"
 DEFAULT_READER_FEATURES_VAR_NAME = "*default-reader-features*"
+DEFAULT_EXCEPT_HOOK_VAR_NAME = "default-except-hook"
+EXCEPT_HOOK_VAR_NAME = "*except-hook*"
 GENERATED_PYTHON_VAR_NAME = "*generated-python*"
 PRINT_GENERATED_PY_VAR_NAME = "*print-generated-python*"
 MAIN_NS_VAR_NAME = "*main-ns*"
@@ -2030,6 +2033,26 @@ def print_generated_python() -> bool:
     )
 
 
+###################
+# Traceback Hooks #
+###################
+
+
+def basilisp_except_hook(
+    tp: Type[BaseException],
+    e: BaseException,
+    tb: Optional[types.TracebackType],
+) -> None:
+    """Basilisp except hook which is installed as `sys.excepthook` to print any
+    unhandled tracebacks."""
+    ns_sym = sym.symbol(EXCEPT_HOOK_VAR_NAME, ns=CORE_NS)
+    return (
+        Maybe(Var.find(ns_sym))
+        .map(lambda hook: hook(e, tp, tb))
+        .or_else_raise(lambda: RuntimeException(f"Dynamic Var {ns_sym} not bound!"))
+    )
+
+
 #########################
 # Bootstrap the Runtime #
 #########################
@@ -2127,7 +2150,7 @@ def in_ns(s: sym.Symbol):
         ),
     )
 
-    # Dynamic Var containing command line arguments passed via `basilisp run`
+    # Dynamic Var containing the name of the main namespace (if one is given)
     Var.intern(
         CORE_NS_SYM,
         sym.symbol(MAIN_NS_VAR_NAME),
@@ -2162,6 +2185,38 @@ def in_ns(s: sym.Symbol):
         ),
     )
 
+    # Var containing the original traceback printer
+    Var.intern(
+        CORE_NS_SYM,
+        sym.symbol(DEFAULT_EXCEPT_HOOK_VAR_NAME),
+        print_exception,
+        meta=lmap.map(
+            {
+                _DOC_META_KEY: (
+                    f"The default value of :lpy:var:`{EXCEPT_HOOK_VAR_NAME}`."
+                )
+            }
+        ),
+    )
+
+    # Dynamic Var containing the current traceback printer
+    Var.intern(
+        CORE_NS_SYM,
+        sym.symbol(EXCEPT_HOOK_VAR_NAME),
+        print_exception,
+        dynamic=True,
+        meta=lmap.map(
+            {
+                _DOC_META_KEY: (
+                    "A function which controls the printing of exceptions. "
+                    "The default function has special handling for compiler errors "
+                    "and reader syntax errors. All other exception types are printed "
+                    "as by `traceback.print_exception <https://docs.python.org/3/library/traceback.html#traceback.print_exception>`_."
+                )
+            }
+        ),
+    )
+
     # Dynamic Vars examined by the compiler for generating Python code for debugging
     Var.intern(
         CORE_NS_SYM,
diff --git a/src/basilisp/lang/source.py b/src/basilisp/lang/source.py
index c5f6bd857..1ea950d1b 100644
--- a/src/basilisp/lang/source.py
+++ b/src/basilisp/lang/source.py
@@ -1,6 +1,6 @@
 import linecache
 import os
-from typing import Optional
+from typing import List, Optional
 
 try:
     import pygments.formatters
@@ -46,7 +46,7 @@ def format_source_context(
     end_line: Optional[int] = None,
     num_context_lines: int = 5,
     show_cause_marker: bool = True,
-) -> list[str]:
+) -> List[str]:
     """Format source code context with line numbers and identifiers for the affected
     line(s)."""
     assert num_context_lines >= 0
diff --git a/src/basilisp/main.py b/src/basilisp/main.py
index 671efee85..69877f3b9 100644
--- a/src/basilisp/main.py
+++ b/src/basilisp/main.py
@@ -1,6 +1,7 @@
 import importlib
 import logging
 import site
+import sys
 from pathlib import Path
 from typing import List, Optional
 
@@ -29,6 +30,7 @@ def init(opts: Optional[CompilerOpts] = None) -> None:
     """
     runtime.init_ns_var()
     runtime.bootstrap_core(opts if opts is not None else compiler_opts())
+    sys.excepthook = runtime.basilisp_except_hook
     importer.hook_imports()
     importlib.import_module("basilisp.core")
 
diff --git a/src/basilisp/prompt.py b/src/basilisp/prompt.py
index 3e09dd51c..5a1ae5819 100644
--- a/src/basilisp/prompt.py
+++ b/src/basilisp/prompt.py
@@ -2,7 +2,6 @@
 
 import os
 import re
-import traceback
 from functools import partial
 from types import MappingProxyType
 from typing import Any, Iterable, Mapping, Optional, Type
@@ -103,8 +102,7 @@ def _(event: KeyPressEvent) -> None:
                 event.current_buffer.insert_text("\n")
             except reader.SyntaxError as e:
                 run_in_terminal(
-                    partial(
-                        print_exception,
+                    lambda: runtime.basilisp_except_hook(
                         reader.SyntaxError,
                         e,
                         e.__traceback__,

From 623cdbf8330e72ef5a3d7dbc482a1251de0a752f Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@Christophers-MacBook-Pro.local>
Date: Wed, 31 Jan 2024 08:39:06 -0500
Subject: [PATCH 09/20] yeah

---
 src/basilisp/prompt.py | 2 --
 1 file changed, 2 deletions(-)

diff --git a/src/basilisp/prompt.py b/src/basilisp/prompt.py
index 5a1ae5819..112205ef5 100644
--- a/src/basilisp/prompt.py
+++ b/src/basilisp/prompt.py
@@ -2,7 +2,6 @@
 
 import os
 import re
-from functools import partial
 from types import MappingProxyType
 from typing import Any, Iterable, Mapping, Optional, Type
 
@@ -17,7 +16,6 @@
 
 from basilisp.lang import reader as reader
 from basilisp.lang import runtime as runtime
-from basilisp.lang.exception import print_exception
 
 _USER_DATA_HOME = os.getenv("XDG_DATA_HOME", os.path.expanduser("~/.local/share"))
 BASILISP_USER_DATA = os.path.abspath(os.path.join(_USER_DATA_HOME, "basilisp"))

From d7fe072e4515797529e6deb0647dacf56ac2750f Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@Christophers-MacBook-Pro.local>
Date: Wed, 31 Jan 2024 09:00:21 -0500
Subject: [PATCH 10/20] Fixes on fixes

---
 src/basilisp/cli.py                     |  1 -
 src/basilisp/lang/compiler/exception.py |  3 +--
 src/basilisp/lang/reader.py             |  2 +-
 src/basilisp/lang/runtime.py            | 12 +++++++-----
 src/basilisp/lang/source.py             |  2 +-
 src/basilisp/prompt.py                  |  4 +++-
 6 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/basilisp/cli.py b/src/basilisp/cli.py
index cc95efb14..ffb5b9eeb 100644
--- a/src/basilisp/cli.py
+++ b/src/basilisp/cli.py
@@ -15,7 +15,6 @@
 from basilisp.lang import runtime as runtime
 from basilisp.lang import symbol as sym
 from basilisp.lang import vector as vec
-from basilisp.lang.exception import print_exception
 from basilisp.prompt import get_prompter
 
 CLI_INPUT_FILE_PATH = "<CLI Input>"
diff --git a/src/basilisp/lang/compiler/exception.py b/src/basilisp/lang/compiler/exception.py
index 7ccdafe5a..c05b1f9ed 100644
--- a/src/basilisp/lang/compiler/exception.py
+++ b/src/basilisp/lang/compiler/exception.py
@@ -1,5 +1,4 @@
 import ast
-import linecache
 from enum import Enum
 from types import TracebackType
 from typing import Any, Dict, List, Optional, Type, Union
@@ -111,7 +110,7 @@ def __str__(self):
 
 
 @format_exception.register(CompilerException)
-def format_compiler_exception(  # pylint: disable=unused-argument
+def format_compiler_exception(  # pylint: disable=too-many-branches,unused-argument
     e: CompilerException, tp: Type[Exception], tb: TracebackType
 ) -> List[str]:
     """Format a compiler exception as a list of newline-terminated strings."""
diff --git a/src/basilisp/lang/reader.py b/src/basilisp/lang/reader.py
index b94e83d2f..ef4430f5d 100644
--- a/src/basilisp/lang/reader.py
+++ b/src/basilisp/lang/reader.py
@@ -157,7 +157,7 @@ def __str__(self):
 
 
 @format_exception.register(SyntaxError)
-def format_syntax_error(  # pylint: disable=unused-argumentma
+def format_syntax_error(  # pylint: disable=unused-argument
     e: SyntaxError, tp: Type[Exception], tb: TracebackType
 ) -> List[str]:
     context_exc: Optional[BaseException] = e.__cause__
diff --git a/src/basilisp/lang/runtime.py b/src/basilisp/lang/runtime.py
index bc35a6df6..ea643ff64 100644
--- a/src/basilisp/lang/runtime.py
+++ b/src/basilisp/lang/runtime.py
@@ -2046,11 +2046,13 @@ def basilisp_except_hook(
     """Basilisp except hook which is installed as `sys.excepthook` to print any
     unhandled tracebacks."""
     ns_sym = sym.symbol(EXCEPT_HOOK_VAR_NAME, ns=CORE_NS)
-    return (
-        Maybe(Var.find(ns_sym))
-        .map(lambda hook: hook(e, tp, tb))
-        .or_else_raise(lambda: RuntimeException(f"Dynamic Var {ns_sym} not bound!"))
-    )
+    if (hook := Var.find(ns_sym)) is not None:
+        hook(e, tp, tb)
+    else:
+        # Emit an error to stderr and fall back to the default Python except hook
+        # if no hook is currently defined in Basilisp.
+        sys.stderr.write(f"Dynamic Var {ns_sym} not bound!")
+        sys.__excepthook__(tp, e, tb)
 
 
 #########################
diff --git a/src/basilisp/lang/source.py b/src/basilisp/lang/source.py
index 1ea950d1b..bd59735f9 100644
--- a/src/basilisp/lang/source.py
+++ b/src/basilisp/lang/source.py
@@ -20,7 +20,7 @@ def _get_formatter_name() -> Optional[str]:
         If `BASILISP_NO_COLOR` is set to a truthy value, use no formatting."""
         if os.environ.get("BASILISP_NO_COLOR", "false").lower() in {"1", "true"}:
             return None
-        elif os.environ.get("COLORTERM", "") in ("truecolor", "24bit"):
+        elif os.environ.get("COLORTERM", "") in {"truecolor", "24bit"}:
             return "terminal16m"
         elif "256" in os.environ.get("TERM", ""):
             return "terminal256"
diff --git a/src/basilisp/prompt.py b/src/basilisp/prompt.py
index 112205ef5..81672f250 100644
--- a/src/basilisp/prompt.py
+++ b/src/basilisp/prompt.py
@@ -2,6 +2,7 @@
 
 import os
 import re
+from functools import partial
 from types import MappingProxyType
 from typing import Any, Iterable, Mapping, Optional, Type
 
@@ -100,7 +101,8 @@ def _(event: KeyPressEvent) -> None:
                 event.current_buffer.insert_text("\n")
             except reader.SyntaxError as e:
                 run_in_terminal(
-                    lambda: runtime.basilisp_except_hook(
+                    partial(
+                        runtime.basilisp_except_hook,
                         reader.SyntaxError,
                         e,
                         e.__traceback__,

From aecfce87a68b5f8ece2f9f43170c6f72ce4d0c6d Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@Christophers-MacBook-Pro.local>
Date: Wed, 31 Jan 2024 09:05:56 -0500
Subject: [PATCH 11/20] And another one

---
 src/basilisp/cli.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/basilisp/cli.py b/src/basilisp/cli.py
index ffb5b9eeb..fcf3e41fe 100644
--- a/src/basilisp/cli.py
+++ b/src/basilisp/cli.py
@@ -4,7 +4,6 @@
 import os
 import sys
 import textwrap
-import traceback
 import types
 from pathlib import Path
 from typing import Any, Callable, Optional, Sequence, Type
@@ -459,7 +458,7 @@ def repl(
                 repl_module.mark_exception(e)
                 continue
             except Exception as e:  # pylint: disable=broad-exception-caught
-                traceback.print_exception(Exception, e, e.__traceback__)
+                runtime.basilisp_except_hook(type(e), e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
 

From 81d5508ff1d5b8f86dc7cef60a4e0d157c6a3de4 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Thu, 8 Feb 2024 11:10:30 -0500
Subject: [PATCH 12/20] More stuff

---
 src/basilisp/cli.py          |  8 +++----
 src/basilisp/lang/runtime.py | 43 ++++++++++++++++++++++++------------
 src/basilisp/main.py         |  2 +-
 src/basilisp/prompt.py       |  3 ++-
 4 files changed, 35 insertions(+), 21 deletions(-)

diff --git a/src/basilisp/cli.py b/src/basilisp/cli.py
index fcf3e41fe..cd3c5848c 100644
--- a/src/basilisp/cli.py
+++ b/src/basilisp/cli.py
@@ -448,17 +448,15 @@ def repl(
                 prompter.print(runtime.lrepr(result))
                 repl_module.mark_repl_result(result)
             except reader.SyntaxError as e:
-                runtime.basilisp_except_hook(reader.SyntaxError, e, e.__traceback__)
+                sys.excepthook(reader.SyntaxError, e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
             except compiler.CompilerException as e:
-                runtime.basilisp_except_hook(
-                    compiler.CompilerException, e, e.__traceback__
-                )
+                sys.excepthook(compiler.CompilerException, e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
             except Exception as e:  # pylint: disable=broad-exception-caught
-                runtime.basilisp_except_hook(type(e), e, e.__traceback__)
+                sys.excepthook(type(e), e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
 
diff --git a/src/basilisp/lang/runtime.py b/src/basilisp/lang/runtime.py
index ea643ff64..a23130d1a 100644
--- a/src/basilisp/lang/runtime.py
+++ b/src/basilisp/lang/runtime.py
@@ -9,6 +9,7 @@
 import logging
 import math
 import numbers
+import os
 import platform
 import re
 import sys
@@ -2038,21 +2039,35 @@ def print_generated_python() -> bool:
 ###################
 
 
-def basilisp_except_hook(
-    tp: Type[BaseException],
-    e: BaseException,
-    tb: Optional[types.TracebackType],
-) -> None:
-    """Basilisp except hook which is installed as `sys.excepthook` to print any
-    unhandled tracebacks."""
+def create_basilisp_except_hook():
+    """Create an except hook which is suitable to being installed as `sys.excepthook`
+    to print any unhandled tracebacks.
+
+    This function must be called after bootstrapping `basilisp.core`."""
     ns_sym = sym.symbol(EXCEPT_HOOK_VAR_NAME, ns=CORE_NS)
-    if (hook := Var.find(ns_sym)) is not None:
-        hook(e, tp, tb)
-    else:
-        # Emit an error to stderr and fall back to the default Python except hook
-        # if no hook is currently defined in Basilisp.
-        sys.stderr.write(f"Dynamic Var {ns_sym} not bound!")
-        sys.__excepthook__(tp, e, tb)
+    hook_var = Var.find(ns_sym)
+    assert hook_var is not None
+
+    def basilisp_except_hook(
+        tp: Type[BaseException],
+        e: BaseException,
+        tb: Optional[types.TracebackType],
+    ) -> None:
+        if (hook := hook_var.value) is not None:
+            try:
+                hook(e, tp, tb)
+            except Exception:
+                sys.__stderr__.write(
+                    f"Exception occurred in Basilisp except hook {ns_sym}{os.linesep}"
+                )
+                sys.__excepthook__(tp, e, tb)
+        else:
+            # Emit an error to stderr and fall back to the default Python except hook
+            # if no hook is currently defined in Basilisp.
+            sys.__stderr__.write(f"Dynamic Var {ns_sym} not bound!{os.linesep}")
+            sys.__excepthook__(tp, e, tb)
+
+    return basilisp_except_hook
 
 
 #########################
diff --git a/src/basilisp/main.py b/src/basilisp/main.py
index 69877f3b9..6b0fe7bef 100644
--- a/src/basilisp/main.py
+++ b/src/basilisp/main.py
@@ -30,7 +30,7 @@ def init(opts: Optional[CompilerOpts] = None) -> None:
     """
     runtime.init_ns_var()
     runtime.bootstrap_core(opts if opts is not None else compiler_opts())
-    sys.excepthook = runtime.basilisp_except_hook
+    sys.excepthook = runtime.create_basilisp_except_hook()
     importer.hook_imports()
     importlib.import_module("basilisp.core")
 
diff --git a/src/basilisp/prompt.py b/src/basilisp/prompt.py
index 81672f250..8add926b2 100644
--- a/src/basilisp/prompt.py
+++ b/src/basilisp/prompt.py
@@ -2,6 +2,7 @@
 
 import os
 import re
+import sys
 from functools import partial
 from types import MappingProxyType
 from typing import Any, Iterable, Mapping, Optional, Type
@@ -102,7 +103,7 @@ def _(event: KeyPressEvent) -> None:
             except reader.SyntaxError as e:
                 run_in_terminal(
                     partial(
-                        runtime.basilisp_except_hook,
+                        sys.excepthook,
                         reader.SyntaxError,
                         e,
                         e.__traceback__,

From 71b0c7de0035e6d30fc54430d0be492648b98a93 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Mon, 12 Feb 2024 21:33:08 -0500
Subject: [PATCH 13/20] Several small things

---
 src/basilisp/core.lpy        |  7 ++++---
 src/basilisp/lang/runtime.py | 15 ---------------
 src/basilisp/stacktrace.lpy  |  6 +++++-
 3 files changed, 9 insertions(+), 19 deletions(-)

diff --git a/src/basilisp/core.lpy b/src/basilisp/core.lpy
index 9054717ba..04b656871 100644
--- a/src/basilisp/core.lpy
+++ b/src/basilisp/core.lpy
@@ -4171,7 +4171,7 @@
   ([]
    (.write *out* os/linesep)
    (when *flush-on-newline*
-       (.flush *out*))
+     (.flush *out*))
    nil)
   ([x]
    (let [stdout *out*]
@@ -4402,11 +4402,12 @@
   (with-open [f (python/open path ** :mode "r")]
     (load-reader f)))
 
-(defn- resolve-load-path [path]
+(defn- resolve-load-path
   "Resolve load ``path`` relative to the current namespace, or, if it
   begins with \"/\", relative to the syspath, and return it.
 
- Throw a python/FileNotFoundError if the ``path`` cannot be resolved."
+  Throw a ``python/FileNotFoundError`` if the ``path`` cannot be resolved."
+  [path]
   (let [path-rel (if (.startswith path "/")
                    path
                    (let [path-parent (-> (name *ns*)
diff --git a/src/basilisp/lang/runtime.py b/src/basilisp/lang/runtime.py
index a23130d1a..b62bdce1b 100644
--- a/src/basilisp/lang/runtime.py
+++ b/src/basilisp/lang/runtime.py
@@ -86,7 +86,6 @@
 COMPILER_OPTIONS_VAR_NAME = "*compiler-options*"
 COMMAND_LINE_ARGS_VAR_NAME = "*command-line-args*"
 DEFAULT_READER_FEATURES_VAR_NAME = "*default-reader-features*"
-DEFAULT_EXCEPT_HOOK_VAR_NAME = "default-except-hook"
 EXCEPT_HOOK_VAR_NAME = "*except-hook*"
 GENERATED_PYTHON_VAR_NAME = "*generated-python*"
 PRINT_GENERATED_PY_VAR_NAME = "*print-generated-python*"
@@ -2202,20 +2201,6 @@ def in_ns(s: sym.Symbol):
         ),
     )
 
-    # Var containing the original traceback printer
-    Var.intern(
-        CORE_NS_SYM,
-        sym.symbol(DEFAULT_EXCEPT_HOOK_VAR_NAME),
-        print_exception,
-        meta=lmap.map(
-            {
-                _DOC_META_KEY: (
-                    f"The default value of :lpy:var:`{EXCEPT_HOOK_VAR_NAME}`."
-                )
-            }
-        ),
-    )
-
     # Dynamic Var containing the current traceback printer
     Var.intern(
         CORE_NS_SYM,
diff --git a/src/basilisp/stacktrace.lpy b/src/basilisp/stacktrace.lpy
index da0c5c86e..c53308621 100644
--- a/src/basilisp/stacktrace.lpy
+++ b/src/basilisp/stacktrace.lpy
@@ -1,5 +1,9 @@
 (ns basilisp.stacktrace
-  "Utility functions for printing stack traces."
+  "Utility functions for printing stack traces.
+
+  Stack traces printed by the functions in this namespace do not respect the function
+  bound to :lpy:var:`*except-hook*`. There is no special handling for reader syntax
+  errors or compiler exceptions."
   (:require [basilisp.string :as str])
   (:import [traceback :as tb]))
 

From c5034bc6901f7fc36f8a371a8663d1d2592693aa Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Wed, 14 Feb 2024 16:10:56 -0500
Subject: [PATCH 14/20] Quiet now

---
 pyproject.toml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pyproject.toml b/pyproject.toml
index 6a8050590..69776f15d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -101,6 +101,7 @@ branch = true
 omit = [
     "*/__version__.py",
     "*/basilisp/contrib/sphinx/*",
+    "*/basilisp/sitecustomize.py",
 ]
 
 [tool.coverage.paths]

From 1207b58653ab865ff72fdc60cda80583d44fa5a8 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Wed, 14 Feb 2024 17:14:56 -0500
Subject: [PATCH 15/20] More

---
 src/basilisp/cli.py            |  10 +--
 src/basilisp/lang/exception.py |  12 +++-
 src/basilisp/lang/runtime.py   | 112 +++++++++++++++++++++++++++++----
 src/basilisp/prompt.py         |  31 ++++++---
 tests/basilisp/prompt_test.py  |   2 +-
 5 files changed, 136 insertions(+), 31 deletions(-)

diff --git a/src/basilisp/cli.py b/src/basilisp/cli.py
index b7e7daf17..421dcdff2 100644
--- a/src/basilisp/cli.py
+++ b/src/basilisp/cli.py
@@ -14,7 +14,6 @@
 from basilisp.lang import runtime as runtime
 from basilisp.lang import symbol as sym
 from basilisp.lang import vector as vec
-from basilisp.lang.exception import print_exception
 from basilisp.prompt import get_prompter
 
 CLI_INPUT_FILE_PATH = "<CLI Input>"
@@ -396,8 +395,9 @@ def repl(
         warn_on_var_indirection=args.warn_on_var_indirection,
     )
     basilisp.init(opts)
+    print_exception = runtime.get_basilisp_repl_exception_hook()
     ctx = compiler.CompilerContext(filename=REPL_INPUT_FILE_PATH, opts=opts)
-    prompter = get_prompter()
+    prompter = get_prompter(print_exception=print_exception)
     eof = object()
 
     # Bind user-settable dynamic Vars to their existing value to allow users to
@@ -449,15 +449,15 @@ def repl(
                 prompter.print(runtime.lrepr(result))
                 repl_module.mark_repl_result(result)
             except reader.SyntaxError as e:
-                print_exception(e, reader.SyntaxError, e.__traceback__)
+                print_exception(reader.SyntaxError, e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
             except compiler.CompilerException as e:
-                print_exception(e, compiler.CompilerException, e.__traceback__)
+                print_exception(compiler.CompilerException, e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
             except Exception as e:  # pylint: disable=broad-exception-caught
-                print_exception(e, Exception, e.__traceback__)
+                print_exception(type(e), e, e.__traceback__)
                 repl_module.mark_exception(e)
                 continue
 
diff --git a/src/basilisp/lang/exception.py b/src/basilisp/lang/exception.py
index 157d4f64a..4a499662f 100644
--- a/src/basilisp/lang/exception.py
+++ b/src/basilisp/lang/exception.py
@@ -1,8 +1,9 @@
 import functools
 import sys
 import traceback
+import types
 from types import TracebackType
-from typing import List, Optional, Type
+from typing import Callable, List, Optional, Type
 
 import attr
 
@@ -24,6 +25,11 @@ def __str__(self):
         return f"{self.message} {lrepr(self.data)}"
 
 
+ExceptionPrinter = Callable[
+    [Type[BaseException], BaseException, Optional[types.TracebackType]], None
+]
+
+
 @functools.singledispatch
 def format_exception(
     e: Optional[BaseException],
@@ -45,9 +51,9 @@ def format_exception(
 
 
 def print_exception(
+    tp: Optional[Type[BaseException]],
     e: Optional[BaseException],
-    tp: Optional[Type[BaseException]] = None,
-    tb: Optional[TracebackType] = None,
+    tb: Optional[TracebackType],
 ) -> None:
     """Print the given exception `e` using Basilisp's own exception formatting.
 
diff --git a/src/basilisp/lang/runtime.py b/src/basilisp/lang/runtime.py
index b62bdce1b..af4fb8718 100644
--- a/src/basilisp/lang/runtime.py
+++ b/src/basilisp/lang/runtime.py
@@ -9,10 +9,10 @@
 import logging
 import math
 import numbers
-import os
 import platform
 import re
 import sys
+import textwrap
 import threading
 import types
 from collections.abc import Sequence, Sized
@@ -47,7 +47,7 @@
 from basilisp.lang import symbol as sym
 from basilisp.lang import vector as vec
 from basilisp.lang.atom import Atom
-from basilisp.lang.exception import print_exception
+from basilisp.lang.exception import ExceptionPrinter, print_exception
 from basilisp.lang.interfaces import (
     IAssociative,
     IBlockingDeref,
@@ -87,6 +87,7 @@
 COMMAND_LINE_ARGS_VAR_NAME = "*command-line-args*"
 DEFAULT_READER_FEATURES_VAR_NAME = "*default-reader-features*"
 EXCEPT_HOOK_VAR_NAME = "*except-hook*"
+REPL_EXCEPT_HOOK_VAR_NAME = "*repl-except-hook*"
 GENERATED_PYTHON_VAR_NAME = "*generated-python*"
 PRINT_GENERATED_PY_VAR_NAME = "*print-generated-python*"
 MAIN_NS_VAR_NAME = "*main-ns*"
@@ -2038,7 +2039,7 @@ def print_generated_python() -> bool:
 ###################
 
 
-def create_basilisp_except_hook():
+def create_basilisp_except_hook() -> ExceptionPrinter:
     """Create an except hook which is suitable to being installed as `sys.excepthook`
     to print any unhandled tracebacks.
 
@@ -2054,16 +2055,49 @@ def basilisp_except_hook(
     ) -> None:
         if (hook := hook_var.value) is not None:
             try:
-                hook(e, tp, tb)
+                hook(tp, e, tb)
             except Exception:
-                sys.__stderr__.write(
-                    f"Exception occurred in Basilisp except hook {ns_sym}{os.linesep}"
+                print(
+                    f"Exception occurred in Basilisp except hook {ns_sym}",
+                    file=sys.__stderr__,
                 )
                 sys.__excepthook__(tp, e, tb)
         else:
             # Emit an error to stderr and fall back to the default Python except hook
             # if no hook is currently defined in Basilisp.
-            sys.__stderr__.write(f"Dynamic Var {ns_sym} not bound!{os.linesep}")
+            print(f"Dynamic Var {ns_sym} not bound!", file=sys.__stderr__)
+            sys.__excepthook__(tp, e, tb)
+
+    return basilisp_except_hook
+
+
+def get_basilisp_repl_exception_hook() -> ExceptionPrinter:
+    """Create an exception hook which can be used to print exception tracebacks for
+    interactive REPL sessions.
+
+    This function must be called after bootstrapping `basilisp.core`."""
+    ns_sym = sym.symbol(REPL_EXCEPT_HOOK_VAR_NAME, ns=CORE_NS)
+    hook_var = Var.find(ns_sym)
+    assert hook_var is not None
+
+    def basilisp_except_hook(
+        tp: Type[BaseException],
+        e: BaseException,
+        tb: Optional[types.TracebackType],
+    ) -> None:
+        if (hook := hook_var.value) is not None:
+            try:
+                hook(tp, e, tb)
+            except Exception:
+                print(
+                    f"Exception occurred in Basilisp REPL except hook {ns_sym}",
+                    file=sys.__stderr__,
+                )
+                sys.__excepthook__(tp, e, tb)
+        else:
+            # Emit an error to stderr and fall back to the default Python except hook
+            # if no hook is currently defined in Basilisp.
+            print(f"Dynamic Var {ns_sym} not bound!", file=sys.__stderr__)
             sys.__excepthook__(tp, e, tb)
 
     return basilisp_except_hook
@@ -2201,7 +2235,7 @@ def in_ns(s: sym.Symbol):
         ),
     )
 
-    # Dynamic Var containing the current traceback printer
+    # Dynamic Vars containing the current traceback printers
     Var.intern(
         CORE_NS_SYM,
         sym.symbol(EXCEPT_HOOK_VAR_NAME),
@@ -2209,11 +2243,63 @@ def in_ns(s: sym.Symbol):
         dynamic=True,
         meta=lmap.map(
             {
-                _DOC_META_KEY: (
-                    "A function which controls the printing of exceptions. "
-                    "The default function has special handling for compiler errors "
-                    "and reader syntax errors. All other exception types are printed "
-                    "as by `traceback.print_exception <https://docs.python.org/3/library/traceback.html#traceback.print_exception>`_."
+                _DOC_META_KEY: textwrap.indent(
+                    textwrap.dedent(
+                        f"""
+                    A function of 3 arguments which controls the printing of unhandled
+                    exceptions.
+
+                    The three arguments should be in order: an exception *type*, an
+                    exception *instance*, and an exception *traceback* (e.g. the value
+                    of the ``__traceback__`` attribute). In the majority of cases, only
+                    the second argument is needed but nevertheless ``sys.excepthook``
+                    is called with all 3 in that order.
+
+                    The default function has special handling for compiler errors
+                    and reader syntax errors. All other exception types are printed
+                    as by `traceback.print_exception <https://docs.python.org/3/library/traceback.html#traceback.print_exception>`_.
+
+                    After bootstrapping the runtime, Python's `sys.excepthook <https://docs.python.org/3/library/sys.html#sys.excepthook>`_
+                    will use the function bound to this Var for printing any unhandled
+                    exceptions, including those not originating from Basilisp code.
+
+                    For controlling the display of exceptions occurring during REPL
+                    sessions, see :lpy:var:`{REPL_EXCEPT_HOOK_VAR_NAME}`.
+                    """
+                    ).strip(),
+                    "  ",
+                )
+            }
+        ),
+    )
+    Var.intern(
+        CORE_NS_SYM,
+        sym.symbol(REPL_EXCEPT_HOOK_VAR_NAME),
+        print_exception,
+        dynamic=True,
+        meta=lmap.map(
+            {
+                _DOC_META_KEY: textwrap.indent(
+                    textwrap.dedent(
+                        f"""
+                    A function of 3 arguments which controls the printing of exceptions
+                    thrown during interactive REPL sessions.
+
+                    The three arguments should be in order: an exception *type*, an
+                    exception *instance*, and an exception *traceback* (e.g. the value
+                    of the ``__traceback__`` attribute). In the majority of cases, only
+                    the second argument is needed but nevertheless ``sys.excepthook``
+                    is called with all 3 in that order.
+
+                    The default function has special handling for compiler errors
+                    and reader syntax errors. All other exception types are printed
+                    as by `traceback.print_exception <https://docs.python.org/3/library/traceback.html#traceback.print_exception>`_.
+
+                    This Var is distinct from :lpy:var:`{EXCEPT_HOOK_VAR_NAME}`, which controls
+                    printing unhandled exceptions occurring outside the REPL context.
+                    """
+                    ).strip(),
+                    "  ",
                 )
             }
         ),
diff --git a/src/basilisp/prompt.py b/src/basilisp/prompt.py
index ca6ad3ee9..4eb601bb5 100644
--- a/src/basilisp/prompt.py
+++ b/src/basilisp/prompt.py
@@ -2,9 +2,11 @@
 
 import os
 import re
+import traceback
+import types
 from functools import partial
 from types import MappingProxyType
-from typing import Any, Iterable, Mapping, Optional, Type
+from typing import Any, Callable, Iterable, Mapping, Optional, Type
 
 from prompt_toolkit import PromptSession
 from prompt_toolkit.application import run_in_terminal
@@ -17,7 +19,7 @@
 
 from basilisp.lang import reader as reader
 from basilisp.lang import runtime as runtime
-from basilisp.lang.exception import print_exception
+from basilisp.lang.exception import ExceptionPrinter
 
 _USER_DATA_HOME = os.getenv("XDG_DATA_HOME", os.path.expanduser("~/.local/share"))
 BASILISP_USER_DATA = os.path.abspath(os.path.join(_USER_DATA_HOME, "basilisp"))
@@ -30,7 +32,13 @@
 
 
 class Prompter:
-    __slots__ = ()
+    __slots__ = ("_print_exception",)
+
+    def __init__(
+        self,
+        print_exception: ExceptionPrinter = traceback.print_exception,
+    ):
+        self._print_exception = print_exception
 
     def prompt(self, msg: str) -> str:
         """Prompt the user for input with the input string `msg`."""
@@ -65,7 +73,11 @@ class PromptToolkitPrompter(Prompter):
 
     __slots__ = ("_session",)
 
-    def __init__(self):
+    def __init__(
+        self,
+        print_exception: ExceptionPrinter = traceback.print_exception,
+    ):
+        super().__init__(print_exception)
         self._session: PromptSession = PromptSession(
             auto_suggest=AutoSuggestFromHistory(),
             completer=REPLCompleter(),
@@ -76,8 +88,7 @@ def __init__(self):
             **self._style_settings,
         )
 
-    @staticmethod
-    def _get_key_bindings() -> KeyBindings:
+    def _get_key_bindings(self) -> KeyBindings:
         """Return `KeyBindings` which override the builtin `enter` handler to
         allow multi-line input.
 
@@ -103,7 +114,7 @@ def _(event: KeyPressEvent) -> None:
             except reader.SyntaxError as e:
                 run_in_terminal(
                     partial(
-                        print_exception,
+                        self._print_exception,
                         reader.SyntaxError,
                         e,
                         e.__traceback__,
@@ -162,12 +173,14 @@ def print(self, msg: str) -> None:
     _DEFAULT_PROMPTER = StyledPromptToolkitPrompter
 
 
-def get_prompter() -> Prompter:
+def get_prompter(
+    print_exception: ExceptionPrinter = traceback.print_exception,
+) -> Prompter:
     """Return a Prompter instance for reading user input from the REPL.
 
     Prompter instances may be stateful, so the Prompter instance returned by
     this function can be reused within a single REPL session."""
-    return _DEFAULT_PROMPTER()
+    return _DEFAULT_PROMPTER(print_exception)
 
 
 __all__ = ["Prompter", "get_prompter"]
diff --git a/tests/basilisp/prompt_test.py b/tests/basilisp/prompt_test.py
index 2b06e1893..d4c87393d 100644
--- a/tests/basilisp/prompt_test.py
+++ b/tests/basilisp/prompt_test.py
@@ -176,7 +176,7 @@ def make_key_press_event(self, text: str):
 
     @pytest.fixture(scope="class")
     def handler(self) -> Binding:
-        kb = PromptToolkitPrompter._get_key_bindings()
+        kb = PromptToolkitPrompter()._get_key_bindings()
         handler, *_ = kb.get_bindings_for_keys((Keys.ControlM,))
         return handler
 

From fd7dfaea65a7b251d8fae0caaf4f596ceb5543f2 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Wed, 14 Feb 2024 18:29:09 -0500
Subject: [PATCH 16/20] Test

---
 src/basilisp/lang/runtime.py   | 53 ++++++++++++----------------------
 src/basilisp/prompt.py         |  3 +-
 tests/basilisp/runtime_test.py | 50 ++++++++++++++++++++++++++++++++
 3 files changed, 70 insertions(+), 36 deletions(-)

diff --git a/src/basilisp/lang/runtime.py b/src/basilisp/lang/runtime.py
index af4fb8718..6760672fc 100644
--- a/src/basilisp/lang/runtime.py
+++ b/src/basilisp/lang/runtime.py
@@ -2039,14 +2039,9 @@ def print_generated_python() -> bool:
 ###################
 
 
-def create_basilisp_except_hook() -> ExceptionPrinter:
-    """Create an except hook which is suitable to being installed as `sys.excepthook`
-    to print any unhandled tracebacks.
-
-    This function must be called after bootstrapping `basilisp.core`."""
-    ns_sym = sym.symbol(EXCEPT_HOOK_VAR_NAME, ns=CORE_NS)
-    hook_var = Var.find(ns_sym)
-    assert hook_var is not None
+def _create_except_hook_fn(hook_var: Var) -> ExceptionPrinter:
+    """Create an except hook function which is mostly compatible with
+    `traceback.print_exception` which uses the function from the Var `hook_var`."""
 
     def basilisp_except_hook(
         tp: Type[BaseException],
@@ -2056,21 +2051,32 @@ def basilisp_except_hook(
         if (hook := hook_var.value) is not None:
             try:
                 hook(tp, e, tb)
-            except Exception:
+            except Exception:  # pylint: disable=broad-exception-caught
                 print(
-                    f"Exception occurred in Basilisp except hook {ns_sym}",
-                    file=sys.__stderr__,
+                    f"Exception occurred in Basilisp except hook {hook_var}",
+                    file=sys.stderr,
                 )
                 sys.__excepthook__(tp, e, tb)
         else:
             # Emit an error to stderr and fall back to the default Python except hook
             # if no hook is currently defined in Basilisp.
-            print(f"Dynamic Var {ns_sym} not bound!", file=sys.__stderr__)
+            print(f"Dynamic Var {hook_var} not bound!", file=sys.stderr)
             sys.__excepthook__(tp, e, tb)
 
     return basilisp_except_hook
 
 
+def create_basilisp_except_hook() -> ExceptionPrinter:
+    """Create an except hook which is suitable to being installed as `sys.excepthook`
+    to print any unhandled tracebacks.
+
+    This function must be called after bootstrapping `basilisp.core`."""
+    ns_sym = sym.symbol(EXCEPT_HOOK_VAR_NAME, ns=CORE_NS)
+    hook_var = Var.find(ns_sym)
+    assert hook_var is not None
+    return _create_except_hook_fn(hook_var)
+
+
 def get_basilisp_repl_exception_hook() -> ExceptionPrinter:
     """Create an exception hook which can be used to print exception tracebacks for
     interactive REPL sessions.
@@ -2079,28 +2085,7 @@ def get_basilisp_repl_exception_hook() -> ExceptionPrinter:
     ns_sym = sym.symbol(REPL_EXCEPT_HOOK_VAR_NAME, ns=CORE_NS)
     hook_var = Var.find(ns_sym)
     assert hook_var is not None
-
-    def basilisp_except_hook(
-        tp: Type[BaseException],
-        e: BaseException,
-        tb: Optional[types.TracebackType],
-    ) -> None:
-        if (hook := hook_var.value) is not None:
-            try:
-                hook(tp, e, tb)
-            except Exception:
-                print(
-                    f"Exception occurred in Basilisp REPL except hook {ns_sym}",
-                    file=sys.__stderr__,
-                )
-                sys.__excepthook__(tp, e, tb)
-        else:
-            # Emit an error to stderr and fall back to the default Python except hook
-            # if no hook is currently defined in Basilisp.
-            print(f"Dynamic Var {ns_sym} not bound!", file=sys.__stderr__)
-            sys.__excepthook__(tp, e, tb)
-
-    return basilisp_except_hook
+    return _create_except_hook_fn(hook_var)
 
 
 #########################
diff --git a/src/basilisp/prompt.py b/src/basilisp/prompt.py
index 4eb601bb5..f972beed1 100644
--- a/src/basilisp/prompt.py
+++ b/src/basilisp/prompt.py
@@ -3,10 +3,9 @@
 import os
 import re
 import traceback
-import types
 from functools import partial
 from types import MappingProxyType
-from typing import Any, Callable, Iterable, Mapping, Optional, Type
+from typing import Any, Iterable, Mapping, Optional, Type
 
 from prompt_toolkit import PromptSession
 from prompt_toolkit.application import run_in_terminal
diff --git a/tests/basilisp/runtime_test.py b/tests/basilisp/runtime_test.py
index df460a1e0..d95b4e578 100644
--- a/tests/basilisp/runtime_test.py
+++ b/tests/basilisp/runtime_test.py
@@ -1,5 +1,6 @@
 import platform
 import sys
+import traceback
 from decimal import Decimal
 from fractions import Fraction
 
@@ -741,3 +742,52 @@ def test_resolve_alias(self, core_ns):
             ) == runtime.resolve_alias(
                 sym.symbol("non-existent-alias-var", ns="wee.woo"), ns=ns
             )
+
+
+class TestExceptHook:
+    @pytest.fixture
+    def hook_var(self) -> runtime.Var:
+        ns_name = "basilisp.except-hook-test"
+        ns_sym = sym.symbol(ns_name)
+        yield runtime.Var.intern(ns_sym, sym.symbol("*except-hook*"), None)
+
+    def test_hook_value_is_nil(self, hook_var: runtime.Var, capsys):
+        hook = runtime._create_except_hook_fn(hook_var)
+
+        try:
+            raise ValueError("Woo!")
+        except ValueError as e:
+            hook(ValueError, e, e.__traceback__)
+
+        res = capsys.readouterr()
+        assert f"Dynamic Var {hook_var} not bound!" in res.err
+
+    def test_hook_throws_exception(self, hook_var: runtime.Var, capsys):
+        def _bad_except_hook(tp, e, tb):
+            raise TypeError("I'm bad at my job!")
+
+        hook_var.bind_root(_bad_except_hook)
+        hook = runtime._create_except_hook_fn(hook_var)
+
+        try:
+            raise ValueError("Woo!")
+        except ValueError as e:
+            hook(ValueError, e, e.__traceback__)
+
+        res = capsys.readouterr()
+        assert f"Exception occurred in Basilisp except hook {hook_var}" in res.err
+
+    def test_hook_success(self, hook_var: runtime.Var, capsys):
+        hook_var.bind_root(traceback.print_exception)
+        hook = runtime._create_except_hook_fn(hook_var)
+
+        try:
+            raise ValueError("Woo!")
+        except ValueError as e:
+            hook(ValueError, e, e.__traceback__)
+
+            res = capsys.readouterr()
+            assert (
+                "".join(traceback.format_exception(ValueError, e, e.__traceback__))
+                == res.err
+            )

From e098351f44baeaf4617459ca65d8745720e8cc01 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Wed, 14 Feb 2024 18:32:00 -0500
Subject: [PATCH 17/20] Yeah

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f0b241d30..03f11da2e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,7 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  * Added support for binding destructuring in `for` bindings (#774)
  * Added `==` as an alias to `=` (#859)
  * Added custom exception formatting for `basilisp.lang.compiler.exception.CompilerException` and `basilisp.lang.reader.SyntaxError` to show more useful details to users on errors (#870)
- * Added `basilisp.core/*except-hook*` to allow users the ability to customize behaviors for printing unhandled exceptions (#???)
+ * Added `basilisp.core/*except-hook*` to allow users the ability to customize behaviors for printing unhandled exceptions (#873)
 
 ### Changed
  * Cause exceptions arising from compilation issues during macroexpansion will no longer be nested for each level of macroexpansion (#852)

From cd5004395d09224ed3f9380680a51f3ed9b89396 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Wed, 14 Feb 2024 18:32:09 -0500
Subject: [PATCH 18/20] Seriously

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 03f11da2e..b0384a62a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,7 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  * Added support for binding destructuring in `for` bindings (#774)
  * Added `==` as an alias to `=` (#859)
  * Added custom exception formatting for `basilisp.lang.compiler.exception.CompilerException` and `basilisp.lang.reader.SyntaxError` to show more useful details to users on errors (#870)
- * Added `basilisp.core/*except-hook*` to allow users the ability to customize behaviors for printing unhandled exceptions (#873)
+ * Added `basilisp.core/*except-hook*` and `basilisp.core/*repl-except-hook*`  to allow users the ability to customize behaviors for printing unhandled exceptions (#873)
 
 ### Changed
  * Cause exceptions arising from compilation issues during macroexpansion will no longer be nested for each level of macroexpansion (#852)

From 574dbaafb4a89514ae66d419eeb5dd3fa610db61 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Thu, 15 Feb 2024 08:52:23 -0500
Subject: [PATCH 19/20] Create keybindings differently

---
 src/basilisp/prompt.py        | 98 +++++++++++++++++------------------
 tests/basilisp/prompt_test.py |  9 +++-
 2 files changed, 55 insertions(+), 52 deletions(-)

diff --git a/src/basilisp/prompt.py b/src/basilisp/prompt.py
index f972beed1..1d8404043 100644
--- a/src/basilisp/prompt.py
+++ b/src/basilisp/prompt.py
@@ -31,13 +31,10 @@
 
 
 class Prompter:
-    __slots__ = ("_print_exception",)
+    __slots__ = ("_key_bindings",)
 
-    def __init__(
-        self,
-        print_exception: ExceptionPrinter = traceback.print_exception,
-    ):
-        self._print_exception = print_exception
+    def __init__(self, key_bindings: KeyBindings):
+        self._key_bindings = key_bindings
 
     def prompt(self, msg: str) -> str:
         """Prompt the user for input with the input string `msg`."""
@@ -48,6 +45,46 @@ def print(self, msg: str) -> None:
         print(msg)
 
 
+def create_key_bindings(
+    print_exception: ExceptionPrinter = traceback.print_exception,
+) -> KeyBindings:
+    """Return `KeyBindings` which override the builtin `enter` handler to
+    allow multi-line input.
+
+    Inputs are read by the reader to determine if they represent valid
+    Basilisp syntax. If an `UnexpectedEOFError` is raised, then allow multiline
+    input. If a more general `SyntaxError` is raised, then the exception will
+    be printed to the terminal. In all other cases, handle the input normally."""
+    kb = KeyBindings()
+    _eof = object()
+
+    @kb.add("enter")
+    def _(event: KeyPressEvent) -> None:
+        try:
+            list(
+                reader.read_str(
+                    event.current_buffer.text,
+                    resolver=runtime.resolve_alias,
+                    eof=_eof,
+                )
+            )
+        except reader.UnexpectedEOFError:
+            event.current_buffer.insert_text("\n")
+        except reader.SyntaxError as e:
+            run_in_terminal(
+                partial(
+                    print_exception,
+                    reader.SyntaxError,
+                    e,
+                    e.__traceback__,
+                )
+            )
+        else:
+            event.current_buffer.validate_and_handle()
+
+    return kb
+
+
 _DELIMITED_WORD_PATTERN = re.compile(r"([^\[\](){\}\s]+)")
 
 
@@ -72,58 +109,18 @@ class PromptToolkitPrompter(Prompter):
 
     __slots__ = ("_session",)
 
-    def __init__(
-        self,
-        print_exception: ExceptionPrinter = traceback.print_exception,
-    ):
-        super().__init__(print_exception)
+    def __init__(self, key_bindings: KeyBindings):
+        super().__init__(key_bindings)
         self._session: PromptSession = PromptSession(
             auto_suggest=AutoSuggestFromHistory(),
             completer=REPLCompleter(),
             history=FileHistory(BASILISP_REPL_HISTORY_FILE_PATH),
-            key_bindings=self._get_key_bindings(),
+            key_bindings=self._key_bindings,
             lexer=self._prompt_toolkit_lexer,
             multiline=True,
             **self._style_settings,
         )
 
-    def _get_key_bindings(self) -> KeyBindings:
-        """Return `KeyBindings` which override the builtin `enter` handler to
-        allow multi-line input.
-
-        Inputs are read by the reader to determine if they represent valid
-        Basilisp syntax. If an `UnexpectedEOFError` is raised, then allow multiline
-        input. If a more general `SyntaxError` is raised, then the exception will
-        be printed to the terminal. In all other cases, handle the input normally."""
-        kb = KeyBindings()
-        _eof = object()
-
-        @kb.add("enter")
-        def _(event: KeyPressEvent) -> None:
-            try:
-                list(
-                    reader.read_str(
-                        event.current_buffer.text,
-                        resolver=runtime.resolve_alias,
-                        eof=_eof,
-                    )
-                )
-            except reader.UnexpectedEOFError:
-                event.current_buffer.insert_text("\n")
-            except reader.SyntaxError as e:
-                run_in_terminal(
-                    partial(
-                        self._print_exception,
-                        reader.SyntaxError,
-                        e,
-                        e.__traceback__,
-                    )
-                )
-            else:
-                event.current_buffer.validate_and_handle()
-
-        return kb
-
     _prompt_toolkit_lexer: Optional["PygmentsLexer"] = None
     _style_settings: Mapping[str, Any] = MappingProxyType({})
 
@@ -179,7 +176,8 @@ def get_prompter(
 
     Prompter instances may be stateful, so the Prompter instance returned by
     this function can be reused within a single REPL session."""
-    return _DEFAULT_PROMPTER(print_exception)
+    key_bindings = create_key_bindings(print_exception)
+    return _DEFAULT_PROMPTER(key_bindings)
 
 
 __all__ = ["Prompter", "get_prompter"]
diff --git a/tests/basilisp/prompt_test.py b/tests/basilisp/prompt_test.py
index d4c87393d..0de95f894 100644
--- a/tests/basilisp/prompt_test.py
+++ b/tests/basilisp/prompt_test.py
@@ -8,7 +8,12 @@
 from prompt_toolkit.keys import Keys
 
 from basilisp.lang.runtime import Namespace
-from basilisp.prompt import PromptToolkitPrompter, REPLCompleter, get_prompter
+from basilisp.prompt import (
+    PromptToolkitPrompter,
+    REPLCompleter,
+    create_key_bindings,
+    get_prompter,
+)
 
 try:
     import pygments
@@ -176,7 +181,7 @@ def make_key_press_event(self, text: str):
 
     @pytest.fixture(scope="class")
     def handler(self) -> Binding:
-        kb = PromptToolkitPrompter()._get_key_bindings()
+        kb = create_key_bindings()
         handler, *_ = kb.get_bindings_for_keys((Keys.ControlM,))
         return handler
 

From 363247ce8bc914473e34d92fc18a5e9bd2e4b5a6 Mon Sep 17 00:00:00 2001
From: Christopher Rink <christopher@ChristophersMBP.cjlocal>
Date: Thu, 15 Feb 2024 09:11:34 -0500
Subject: [PATCH 20/20] Missed this one

---
 src/basilisp/contrib/nrepl_server.lpy | 3 ++-
 tests/basilisp/cli_test.py            | 7 +++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/basilisp/contrib/nrepl_server.lpy b/src/basilisp/contrib/nrepl_server.lpy
index 4255b1819..b46f3e26d 100644
--- a/src/basilisp/contrib/nrepl_server.lpy
+++ b/src/basilisp/contrib/nrepl_server.lpy
@@ -355,13 +355,14 @@
       log-response-mw
       response-for-mw))
 
-(defn- on-connect [tcp-req-handler opts]
+(defn- on-connect
   "Serve a new nREPL connection as found in ``tcp-req-handler`` according to ``opts``.
 
   ``opts`` is a map of options with the following optional keys.
 
   :recv-buffer-size The buffer size to using for incoming nREPL
   messages."
+  [tcp-req-handler opts]
   (let [{:keys [recv-buffer-size]
          :or {recv-buffer-size 1024}} opts
         socket                        (.-request tcp-req-handler)
diff --git a/tests/basilisp/cli_test.py b/tests/basilisp/cli_test.py
index 801597dc4..58aa346f8 100644
--- a/tests/basilisp/cli_test.py
+++ b/tests/basilisp/cli_test.py
@@ -14,8 +14,8 @@
 import attr
 import pytest
 
+from basilisp import prompt
 from basilisp.cli import BOOL_FALSE, BOOL_TRUE, invoke_cli
-from basilisp.prompt import Prompter
 
 
 @pytest.fixture(autouse=True)
@@ -172,7 +172,10 @@ def test_run_nrepl(self, run_cli):
 class TestREPL:
     @pytest.fixture(scope="class", autouse=True)
     def prompter(self):
-        with patch("basilisp.cli.get_prompter", return_value=Prompter()):
+        key_bindings = prompt.create_key_bindings()
+        with patch(
+            "basilisp.cli.get_prompter", return_value=prompt.Prompter(key_bindings)
+        ):
             yield
 
     def test_no_input(self, run_cli):