From 07abd19c7d6b643f33ab93c03e3c20057c204c3b Mon Sep 17 00:00:00 2001
From: yamacir-kit <httperror@404-notfound.jp>
Date: Sat, 1 Jun 2024 21:39:02 +0900
Subject: [PATCH] Update the struct `error` to inherit from `std::exception`

Signed-off-by: yamacir-kit <httperror@404-notfound.jp>
---
 README.md                                     |  6 ++--
 VERSION                                       |  2 +-
 include/meevax/kernel/dynamic_environment.hpp |  8 ++---
 include/meevax/kernel/error.hpp               |  8 +++--
 src/kernel/error.cpp                          | 36 +++++++++++--------
 5 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/README.md b/README.md
index 2b90aa2cb..aa563887b 100644
--- a/README.md
+++ b/README.md
@@ -90,7 +90,7 @@ Procedures for each standard are provided by the following R7RS-style libraries:
 cmake -B build -DCMAKE_BUILD_TYPE=Release
 cd build
 make package
-sudo apt install build/meevax_0.5.188_amd64.deb
+sudo apt install build/meevax_0.5.189_amd64.deb
 ```
 
 or
@@ -122,9 +122,9 @@ sudo rm -rf /usr/local/share/meevax
 
 | Target Name | Description
 |-------------|-------------
-| `all`       | Build shared-library `libmeevax.0.5.188.so` and executable `meevax`
+| `all`       | Build shared-library `libmeevax.0.5.189.so` and executable `meevax`
 | `test`      | Test executable `meevax`
-| `package`   | Generate debian package `meevax_0.5.188_amd64.deb`
+| `package`   | Generate debian package `meevax_0.5.189_amd64.deb`
 | `install`   | Copy files into `/usr/local` directly
 
 ## Usage
diff --git a/VERSION b/VERSION
index 0de0d7ec3..a8816aa2e 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.5.188
+0.5.189
diff --git a/include/meevax/kernel/dynamic_environment.hpp b/include/meevax/kernel/dynamic_environment.hpp
index b51f26c9f..8dcf56e03 100644
--- a/include/meevax/kernel/dynamic_environment.hpp
+++ b/include/meevax/kernel/dynamic_environment.hpp
@@ -525,14 +525,14 @@ inline namespace kernel
           }();
         }
       }
-      catch (std::exception const& exception)
-      {
-        return reraise(make<error>(make<string>(exception.what())));
-      }
       catch (error const& error)
       {
         return reraise(make(error));
       }
+      catch (std::exception const& exception)
+      {
+        return reraise(make<error>(make<string>(exception.what())));
+      }
     }
   };
 } // namespace kernel
diff --git a/include/meevax/kernel/error.hpp b/include/meevax/kernel/error.hpp
index b8e6af5e3..297dcc249 100644
--- a/include/meevax/kernel/error.hpp
+++ b/include/meevax/kernel/error.hpp
@@ -25,6 +25,7 @@ namespace meevax
 inline namespace kernel
 {
   struct error : public virtual pair // (<message> . <irritants>)
+               , public std::exception
   {
     struct detail
     {
@@ -37,8 +38,12 @@ inline namespace kernel
 
     std::vector<detail> details {};
 
+    mutable std::string brief {};
+
     using pair::pair;
 
+    ~error() override = default;
+
     template <typename... Ts>
     auto append(Ts&&... xs) -> auto &
     {
@@ -59,8 +64,7 @@ inline namespace kernel
 
     auto report(std::ostream &) const -> std::ostream &;
 
-    [[deprecated]]
-    auto what() const -> std::string;
+    auto what() const noexcept -> char const* override;
   };
 
   auto operator <<(std::ostream &, error const&) -> std::ostream &;
diff --git a/src/kernel/error.cpp b/src/kernel/error.cpp
index e94e8fc91..b37d9db96 100644
--- a/src/kernel/error.cpp
+++ b/src/kernel/error.cpp
@@ -39,14 +39,7 @@ inline namespace kernel
 
   auto error::report(std::ostream & output) const -> std::ostream &
   {
-    output << red("; error! ", static_cast<std::string>(message().as<string>()));
-
-    if (irritants())
-    {
-      output << red(": ", irritants());
-    }
-
-    output << std::endl;
+    output << red("; error! ", what()) << std::endl;
 
     for (auto iter = details.rbegin(); iter != details.rend(); ++iter)
     {
@@ -56,18 +49,31 @@ inline namespace kernel
     return output;
   }
 
-  auto error::what() const -> std::string
+  auto error::what() const noexcept -> char const*
   {
-    std::stringstream ss {};
+    try
+    {
+      if (brief.empty())
+      {
+        auto output = std::stringstream();
 
-    ss << "error: " << static_cast<std::string>(message().as<string>());
+        output << static_cast<std::string>(message().as<string>());
 
-    if (irritants())
+        if (irritants())
+        {
+          output << ": " << irritants();
+        }
+
+        brief = output.str();
+      }
+
+      return brief.c_str();
+    }
+    catch (...)
     {
-      ss << ": " << irritants();
+      std::cerr << "meevax::error::what failed to create an explanatory string for std::exception::what" << std::endl;
+      std::exit(EXIT_FAILURE);
     }
-
-    return ss.str();
   }
 
   auto operator <<(std::ostream & os, error const& datum) -> std::ostream &