diff --git a/include/cpp2util.h b/include/cpp2util.h
index dee5bd2a9..4aead2ae1 100644
--- a/include/cpp2util.h
+++ b/include/cpp2util.h
@@ -2078,6 +2078,93 @@ constexpr auto as( X&& x ) -> decltype(auto) {
 }
 
 
+
+//-------------------------------------------------------------------------------------------------------------
+//  std::expected is and as
+//
+#ifdef __cpp_lib_expected
+
+//  is Type
+//
+template<typename T, typename X>
+    requires std::is_same_v<X, std::expected<T, typename X::error_type>>
+constexpr auto is(X const& x) -> bool
+{
+    return x.has_value();
+}
+
+template<typename T, typename U, typename V>
+    requires std::is_same_v<T, empty>
+constexpr auto is(std::expected<U, V> const& x) -> bool
+{
+    return !x.has_value();
+}
+
+//  is std::unexpected<T> Type
+//
+template<typename T, typename X>
+    requires (
+        std::is_same_v<T, std::unexpected<typename X::error_type>>
+        && std::is_same_v<X, std::expected<typename X::value_type, typename X::error_type>>
+    )
+constexpr auto is(X const& x) -> bool
+{
+    return !x.has_value();
+}
+
+
+//  is Value
+//
+template<typename T, typename U>
+constexpr auto is(std::expected<T, U> const& x, auto&& value) -> bool
+{
+    //  Predicate case
+    if constexpr (requires{ bool{ value(x) }; }) {
+        return value(x);
+    }
+    else if constexpr (std::is_function_v<decltype(value)> || requires{ &value.operator(); }) {
+        return false;
+    }
+
+    //  Value case
+    else if constexpr (requires{ bool{ x.value() == value }; }) {
+        return x.has_value() && x.value() == value;
+    }
+    else {
+        return false;
+    }
+}
+
+
+//  as
+//
+template<typename T, typename X>
+    requires std::is_same_v<X, std::expected<T, typename X::error_type>>
+constexpr auto as(X const& x) -> decltype(auto)
+{
+    return x.value();
+}
+
+//  as std::unexpected<T>
+//
+template<typename T, typename X>
+    requires (
+        std::is_same_v<T, std::unexpected<typename X::error_type>>
+        && std::is_same_v<X, std::expected<typename X::value_type, typename X::error_type>>
+    )
+constexpr auto as(X const& x) -> decltype(auto)
+{
+    // It's UB to call `error` if `has_value` is true.
+    if (x.has_value()) {
+        Throw(
+            std::runtime_error("Cannot cast 'expected' to 'unexpected' because it has a value"),
+            "Cannot cast 'expected' to 'unexpected' because it has a value");
+    }
+
+    return std::unexpected<typename X::error_type>(x.error());
+}
+#endif
+
 } // impl
 
 
diff --git a/regression-tests/pure2-expected-is-as.cpp2 b/regression-tests/pure2-expected-is-as.cpp2
new file mode 100644
index 000000000..d144b2770
--- /dev/null
+++ b/regression-tests/pure2-expected-is-as.cpp2
@@ -0,0 +1,90 @@
+// `std::expected` requires C++23 so a dedicated test file is needed
+// since only MSVC supports it at time of writing, and there's no #ifdef
+// or `static if` support in Cpp2 (yet?).
+
+main: () -> int = {
+    
+    ex1: std::expected<int, int> = (123);
+    ex2: std::expected<int, int> = std::unexpected(-1);
+    ex3: std::expected<std::string, size_t> = ("Expect the unexpected");
+
+    if ex1 is int {
+        std::cout << "ex1 is int\n";
+    }
+
+    if ex1 is bool {
+        std::cout << "BUG - ex1 is not a bool\n";
+        return -1;
+    }
+
+    if ex1 is void {
+        std::cout << "BUG - ex1 is not 'empty'\n";
+        return -1;
+    }
+
+    if ex1 is std::unexpected<int> {
+        std::cout << "BUG - ex1 is not unexpected\n";
+        return -1;
+    }
+
+    if ex1 is 123 {
+        std::cout << "ex1 is 123\n";
+    }
+
+    if ex1 is 100 {
+        std::cout << "BUG - ex1's value is not 100\n";
+        return -1;
+    }
+
+    val1:= ex1 as int;
+    std::cout << "ex1 as int = " << val1 << "\n";
+
+    if ex2 is int {
+        std::cout << "BUG - ex2 is not an int\n";
+        return -1;
+    }
+
+    if ex2 is bool {
+        std::cout << "BUG - ex2 is not a bool\n";
+        return -1;
+    }
+
+    if ex2 is 123 {
+        std::cout << "BUG - ex2 does not have a value\n";
+        return -1;
+    }
+
+    if ex2 is std::unexpected<int> {
+        std::cout << "ex2 is unexpected<int> and error is: " << ex2.error() << "\n";
+    }
+
+    if ex2 is void {
+        std::cout << "ex2 is 'empty' aka unexpected<int> and error is: " << ex2.error() << "\n";
+    }
+
+    ex2_err:= ex2 as std::unexpected<int>;
+    std::cout << "ex2 as std::unexpected<int> and error = " << ex2_err.error() << "\n";
+
+    test_inspect(ex1, "expected<int, int> with value");
+    test_inspect(ex2, "expected<int, int> with unexpected");
+    test_inspect(ex3, "expected<string, size_t> with value");
+
+    return 0;
+}
+
+test_inspect: ( x: _, msg: _ ) = {
+
+    unwrap:= :(unexp: std::unexpected<int>) -> _ = {
+        return unexp.error();
+    };
+
+    std::cout
+        << "\n" << msg << "\n    ..."
+        << inspect x -> std::string {
+            is int = "integer " + std::to_string(x as int);
+            is std::unexpected<int> = "unexpected<int> " + std::to_string(unwrap(x as std::unexpected<int>));
+            is std::string = "string " + x as std::string;
+            is _   = " no match";
+        }
+        << "\n";
+}
\ No newline at end of file
diff --git a/regression-tests/run-tests.sh b/regression-tests/run-tests.sh
index b4cfc8787..6e3ac81b7 100644
--- a/regression-tests/run-tests.sh
+++ b/regression-tests/run-tests.sh
@@ -135,28 +135,11 @@ if [ -z "$label" ]; then
     usage
 fi
 
-tests=$(ls | grep ".cpp2$")
-if [[ -n "$chosen_tests" ]]; then
-    for test in $chosen_tests; do
-        if ! [[ -f "$test" ]]; then
-            echo "Requested test ($test) not found"
-            exit 1
-        fi
-    done
-    echo "Performing tests:"
-    for test in $chosen_tests; do
-        echo "    $test"
-    done
-    echo
-    tests="$chosen_tests"
-else
-    printf "Performing all regression tests\n\n"
-fi
-
-expected_results_dir="test-results"
-
 ################
 # Get the directory with the exec outputs and compilation command
+# We also allow each compiler configuration to specify any test files(s) to exclude from running.
+expected_results_dir="test-results"
+exclude_test_filter=""
 if [[ "$cxx_compiler" == *"cl.exe"* ]]; then
     compiler_cmd="cl.exe -nologo -std:${cxx_std} -MD -EHsc -I ..\..\..\include -Fe:"
     exec_out_dir="$expected_results_dir/msvc-2022-${cxx_std}"
@@ -174,6 +157,12 @@ else
     if [[ "$compiler_version" == *"Apple clang version 14.0"* ||
           "$compiler_version" == *"Homebrew clang version 15.0"* ]]; then
         exec_out_dir="$expected_results_dir/apple-clang-14"
+        # We share the expected results dir for these two compilers, but there is one
+        # test which (as expected) fails to compile on both compilers, but has a slightly
+        # different error diagnostic because the clang path differs. So we exclude it from
+        # running. The alternative would be to duplicate the expected results files, which
+        # seems wasteful for just one test (that doesn't even compile).
+        exclude_test_filter="pure2-expected-is-as.cpp2"
     elif [[ "$compiler_version" == *"Apple clang version 15.0"* ]]; then
         exec_out_dir="$expected_results_dir/apple-clang-15"
     elif [[ "$compiler_version" == *"clang version 12.0"* ]]; then 
@@ -236,6 +225,30 @@ else
     exit 2
 fi
 
+################
+# Get the list of .cpp2 test files
+if [[ -n "$exclude_test_filter" ]]; then
+    tests=$(ls | grep ".cpp2$" | grep -v $exclude_test_filter)
+else
+    tests=$(ls | grep ".cpp2$")
+fi
+if [[ -n "$chosen_tests" ]]; then
+    for test in $chosen_tests; do
+        if ! [[ -f "$test" ]]; then
+            echo "Requested test ($test) not found"
+            exit 1
+        fi
+    done
+    echo "Performing tests:"
+    for test in $chosen_tests; do
+        echo "    $test"
+    done
+    echo
+    tests="$chosen_tests"
+else
+    printf "Performing all regression tests\n\n"
+fi
+
 ################
 cppfront_cmd="cppfront.exe"
 echo "Building cppfront"
diff --git a/regression-tests/test-results/apple-clang-14-c++2b/pure2-expected-is-as.cpp.output b/regression-tests/test-results/apple-clang-14-c++2b/pure2-expected-is-as.cpp.output
new file mode 100644
index 000000000..7280779fa
--- /dev/null
+++ b/regression-tests/test-results/apple-clang-14-c++2b/pure2-expected-is-as.cpp.output
@@ -0,0 +1,63 @@
+pure2-expected-is-as.cpp2:7:10: error: no member named 'expected' in namespace 'std'
+    std::expected<int,int> ex1 {123}; 
+    ~~~~~^
+pure2-expected-is-as.cpp2:7:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex1 {123}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:8:10: error: no member named 'expected' in namespace 'std'
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+    ~~~~~^
+pure2-expected-is-as.cpp2:8:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:9:10: error: no member named 'expected' in namespace 'std'
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+    ~~~~~^
+pure2-expected-is-as.cpp2:9:30: error: expected '(' for function-style cast or type construction
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+                  ~~~~~~~~~~~^
+pure2-expected-is-as.cpp2:11:29: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is<int>(ex1)) {
+                            ^
+pure2-expected-is-as.cpp2:15:30: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is<bool>(ex1)) {
+                             ^
+pure2-expected-is-as.cpp2:20:30: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is<void>(ex1)) {
+                             ^
+pure2-expected-is-as.cpp2:25:29: error: no member named 'unexpected' in namespace 'std'
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                       ~~~~~^
+pure2-expected-is-as.cpp2:25:43: error: expected '(' for function-style cast or type construction
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                                       ~~~^
+pure2-expected-is-as.cpp2:25:46: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                                             ^~~
+                                             exp
+/Applications/Xcode_14.3.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/math.h:895:1: note: 'exp' declared here
+exp(_A1 __lcpp_x) _NOEXCEPT {return ::exp((double)__lcpp_x);}
+^
+pure2-expected-is-as.cpp2:30:24: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is(ex1, 123)) {
+                       ^
+pure2-expected-is-as.cpp2:34:24: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is(ex1, 100)) {
+                       ^
+pure2-expected-is-as.cpp2:39:37: error: use of undeclared identifier 'ex1'
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+                                    ^
+pure2-expected-is-as.cpp2:42:29: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is<int>(ex2)) {
+                            ^
+pure2-expected-is-as.cpp2:47:30: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is<bool>(ex2)) {
+                             ^
+pure2-expected-is-as.cpp2:52:24: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is(ex2, 123)) {
+                       ^
+pure2-expected-is-as.cpp2:57:29: error: no member named 'unexpected' in namespace 'std'
+    if (cpp2::impl::is<std::unexpected<int>>(ex2)) {
+                       ~~~~~^
+fatal error: too many errors emitted, stopping now [-ferror-limit=]
+20 errors generated.
diff --git a/regression-tests/test-results/apple-clang-15-c++2b/pure2-expected-is-as.cpp.execution b/regression-tests/test-results/apple-clang-15-c++2b/pure2-expected-is-as.cpp.execution
new file mode 100644
index 000000000..5483d6cd7
--- /dev/null
+++ b/regression-tests/test-results/apple-clang-15-c++2b/pure2-expected-is-as.cpp.execution
@@ -0,0 +1,15 @@
+ex1 is int
+ex1 is 123
+ex1 as int = 123
+ex2 is unexpected<int> and error is: -1
+ex2 is 'empty' aka unexpected<int> and error is: -1
+ex2 as std::unexpected<int> and error = -1
+
+expected<int, int> with value
+    ...integer 123
+
+expected<int, int> with unexpected
+    ...unexpected<int> -1
+
+expected<string, size_t> with value
+    ...string Expect the unexpected
diff --git a/regression-tests/test-results/clang-12-c++20/pure2-expected-is-as.cpp.output b/regression-tests/test-results/clang-12-c++20/pure2-expected-is-as.cpp.output
new file mode 100644
index 000000000..78c70e989
--- /dev/null
+++ b/regression-tests/test-results/clang-12-c++20/pure2-expected-is-as.cpp.output
@@ -0,0 +1,169 @@
+pure2-expected-is-as.cpp2:7:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex1 {123}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:7:10: error: no member named 'expected' in namespace 'std'; did you mean 'unexpected'?
+    std::expected<int,int> ex1 {123}; 
+    ~~~~~^~~~~~~~
+         unexpected
+/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/exception:92:8: note: 'unexpected' declared here
+  void unexpected() __attribute__ ((__noreturn__));
+       ^
+pure2-expected-is-as.cpp2:8:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:8:10: error: no member named 'expected' in namespace 'std'; did you mean 'unexpected'?
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+    ~~~~~^~~~~~~~
+         unexpected
+/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/exception:92:8: note: 'unexpected' declared here
+  void unexpected() __attribute__ ((__noreturn__));
+       ^
+pure2-expected-is-as.cpp2:9:30: error: expected '(' for function-style cast or type construction
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+                  ~~~~~~~~~~~^
+pure2-expected-is-as.cpp2:9:10: error: no member named 'expected' in namespace 'std'; did you mean 'unexpected'?
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+    ~~~~~^~~~~~~~
+         unexpected
+/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/exception:92:8: note: 'unexpected' declared here
+  void unexpected() __attribute__ ((__noreturn__));
+       ^
+pure2-expected-is-as.cpp2:11:29: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<int>(ex1)) {
+                            ^~~
+                            exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:15:30: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<bool>(ex1)) {
+                             ^~~
+                             exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:20:30: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<void>(ex1)) {
+                             ^~~
+                             exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:25:29: error: 'unexpected' does not name a template but is followed by template arguments
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                            ^         ~~~~~
+/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/exception:92:8: note: non-template declaration found by name lookup
+  void unexpected() __attribute__ ((__noreturn__));
+       ^
+pure2-expected-is-as.cpp2:25:46: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                                             ^~~
+                                             exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:30:24: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is(ex1, 123)) {
+                       ^~~
+                       exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:34:24: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is(ex1, 100)) {
+                       ^~~
+                       exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+In file included from pure2-expected-is-as.cpp:7:
+../../../include/cpp2util.h:1770:72: error: invalid application of 'sizeof' to a function type
+    (std::is_floating_point_v<From> && std::is_floating_point_v<To> && sizeof(From) > sizeof(To)) || // NOLINT(misc-redundant-expression)
+                                                                       ^~~~~~~~~~~~
+../../../include/cpp2util.h:2891:19: note: in instantiation of variable template specialization 'cpp2::impl::is_narrowing_v' requested here
+    if constexpr (is_narrowing_v<C, CPP2_TYPEOF(x)>) {
+                  ^
+pure2-expected-is-as.cpp2:39:28: note: in instantiation of function template specialization 'cpp2::impl::as_<int, double (&)(double) noexcept>' requested here
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+                           ^
+In file included from pure2-expected-is-as.cpp:7:
+../../../include/cpp2util.h:2911:12: error: no matching function for call to 'as'
+    return as<C>(CPP2_FORWARD(x));
+           ^~~~~
+pure2-expected-is-as.cpp2:39:28: note: in instantiation of function template specialization 'cpp2::impl::as_<int, double (&)(double) noexcept>' requested here
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+                           ^
+../../../include/cpp2util.h:1838:16: note: candidate template ignored: constraints not satisfied [with C = int, x:auto = double (&)(double) noexcept]
+constexpr auto as(auto&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+               ^
+../../../include/cpp2util.h:1844:18: note: because 'std::is_scalar_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+                (std::is_scalar_v<CPP2_TYPEOF(x)> && !std::is_enum_v<CPP2_TYPEOF(x)>)
+                 ^
+../../../include/cpp2util.h:1845:17: note: and 'std::is_floating_point_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+            ||  std::is_floating_point_v<CPP2_TYPEOF(x)>
+                ^
+../../../include/cpp2util.h:1846:17: note: and 'std::is_base_of_v<int, std::remove_cvref_t<decltype(x)> >' evaluated to false
+            ||  std::is_base_of_v<C, CPP2_TYPEOF(x)>
+                ^
+../../../include/cpp2util.h:1847:17: note: and 'std::is_base_of_v<std::remove_cvref_t<decltype(x)>, int>' evaluated to false
+            ||  std::is_base_of_v<CPP2_TYPEOF(x), C>
+                ^
+../../../include/cpp2util.h:1848:30: note: and 'C({std::forward<decltype(x)>(x)})' would be invalid: cannot initialize a value of type 'int' with an lvalue of type 'double (double) noexcept'
+            ||  requires { C{CPP2_FORWARD(x)}; }
+                             ^
+../../../include/cpp2util.h:325:37: note: expanded from macro 'CPP2_FORWARD'
+#define CPP2_FORWARD(x)             std::forward<decltype(x)>(x)
+                                    ^
+../../../include/cpp2util.h:1977:6: note: candidate template ignored: constraints not satisfied [with C = int, X = double (&)(double) noexcept]
+auto as(X&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+     ^
+../../../include/cpp2util.h:1976:23: note: because 'specialization_of_template<double (&)(double) noexcept, std::variant>' evaluated to false
+template< typename C, specialization_of_template<std::variant> X >
+                      ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+    { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      ^
+../../../include/cpp2util.h:2024:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+constexpr auto as( X && x ) -> decltype(auto) {
+               ^
+../../../include/cpp2util.h:2023:22: note: because 'same_type_as<double (&)(double) noexcept, std::any>' evaluated to false
+template<typename T, same_type_as<std::any> X>
+                     ^
+../../../include/cpp2util.h:754:29: note: because 'std::same_as<std::remove_cvref_t<double (&)(double) noexcept>, std::remove_cvref_t<any> >' evaluated to false
+concept same_type_as = std::same_as<std::remove_cvref_t<X>, std::remove_cvref_t<C>>;
+                            ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/concepts:63:19: note: because '__detail::__same_as<double (double) noexcept, std::any>' evaluated to false
+      = __detail::__same_as<_Tp, _Up> && __detail::__same_as<_Up, _Tp>;
+                  ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/concepts:57:27: note: because 'std::is_same_v<double (double) noexcept, std::any>' evaluated to false
+      concept __same_as = std::is_same_v<_Tp, _Up>;
+                          ^
+../../../include/cpp2util.h:2069:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+constexpr auto as( X&& x ) -> decltype(auto) { 
+               ^
+../../../include/cpp2util.h:2068:22: note: because 'specialization_of_template<double (&)(double) noexcept, std::optional>' evaluated to false
+template<typename T, specialization_of_template<std::optional> X>
+                     ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+    { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      ^
+../../../include/cpp2util.h:1813:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+constexpr auto as() -> auto
+               ^
+../../../include/cpp2util.h:1824:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+constexpr auto as() -> auto
+               ^
+pure2-expected-is-as.cpp2:39:37: error: use of undeclared identifier 'ex1'
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+                                    ^
+pure2-expected-is-as.cpp2:42:29: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is<int>(ex2)) {
+                            ^
+pure2-expected-is-as.cpp2:47:30: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is<bool>(ex2)) {
+                             ^
+pure2-expected-is-as.cpp2:52:24: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is(ex2, 123)) {
+                       ^
+fatal error: too many errors emitted, stopping now [-ferror-limit=]
+20 errors generated.
diff --git a/regression-tests/test-results/clang-15-c++20-libcpp/pure2-expected-is-as.cpp.output b/regression-tests/test-results/clang-15-c++20-libcpp/pure2-expected-is-as.cpp.output
new file mode 100644
index 000000000..657d2b8ed
--- /dev/null
+++ b/regression-tests/test-results/clang-15-c++20-libcpp/pure2-expected-is-as.cpp.output
@@ -0,0 +1,63 @@
+pure2-expected-is-as.cpp2:7:10: error: no member named 'expected' in namespace 'std'
+    std::expected<int,int> ex1 {123}; 
+    ~~~~~^
+pure2-expected-is-as.cpp2:7:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex1 {123}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:8:10: error: no member named 'expected' in namespace 'std'
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+    ~~~~~^
+pure2-expected-is-as.cpp2:8:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:9:10: error: no member named 'expected' in namespace 'std'
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+    ~~~~~^
+pure2-expected-is-as.cpp2:9:30: error: expected '(' for function-style cast or type construction
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+                  ~~~~~~~~~~~^
+pure2-expected-is-as.cpp2:11:29: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is<int>(ex1)) {
+                            ^
+pure2-expected-is-as.cpp2:15:30: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is<bool>(ex1)) {
+                             ^
+pure2-expected-is-as.cpp2:20:30: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is<void>(ex1)) {
+                             ^
+pure2-expected-is-as.cpp2:25:29: error: no member named 'unexpected' in namespace 'std'
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                       ~~~~~^
+pure2-expected-is-as.cpp2:25:43: error: expected '(' for function-style cast or type construction
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                                       ~~~^
+pure2-expected-is-as.cpp2:25:46: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                                             ^~~
+                                             exp
+/usr/lib/llvm-15/bin/../include/c++/v1/math.h:895:1: note: 'exp' declared here
+exp(_A1 __lcpp_x) _NOEXCEPT {return ::exp((double)__lcpp_x);}
+^
+pure2-expected-is-as.cpp2:30:24: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is(ex1, 123)) {
+                       ^
+pure2-expected-is-as.cpp2:34:24: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is(ex1, 100)) {
+                       ^
+pure2-expected-is-as.cpp2:39:37: error: use of undeclared identifier 'ex1'
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+                                    ^
+pure2-expected-is-as.cpp2:42:29: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is<int>(ex2)) {
+                            ^
+pure2-expected-is-as.cpp2:47:30: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is<bool>(ex2)) {
+                             ^
+pure2-expected-is-as.cpp2:52:24: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is(ex2, 123)) {
+                       ^
+pure2-expected-is-as.cpp2:57:29: error: no member named 'unexpected' in namespace 'std'
+    if (cpp2::impl::is<std::unexpected<int>>(ex2)) {
+                       ~~~~~^
+fatal error: too many errors emitted, stopping now [-ferror-limit=]
+20 errors generated.
diff --git a/regression-tests/test-results/clang-15-c++20/pure2-expected-is-as.cpp.output b/regression-tests/test-results/clang-15-c++20/pure2-expected-is-as.cpp.output
new file mode 100644
index 000000000..613220d97
--- /dev/null
+++ b/regression-tests/test-results/clang-15-c++20/pure2-expected-is-as.cpp.output
@@ -0,0 +1,245 @@
+pure2-expected-is-as.cpp2:7:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex1 {123}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:7:10: error: no member named 'expected' in namespace 'std'; did you mean 'unexpected'?
+    std::expected<int,int> ex1 {123}; 
+    ~~~~~^~~~~~~~
+         unexpected
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/exception:109:8: note: 'unexpected' declared here
+  void unexpected() __attribute__ ((__noreturn__));
+       ^
+pure2-expected-is-as.cpp2:8:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:8:10: error: no member named 'expected' in namespace 'std'; did you mean 'unexpected'?
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+    ~~~~~^~~~~~~~
+         unexpected
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/exception:109:8: note: 'unexpected' declared here
+  void unexpected() __attribute__ ((__noreturn__));
+       ^
+pure2-expected-is-as.cpp2:9:30: error: expected '(' for function-style cast or type construction
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+                  ~~~~~~~~~~~^
+pure2-expected-is-as.cpp2:9:10: error: no member named 'expected' in namespace 'std'; did you mean 'unexpected'?
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+    ~~~~~^~~~~~~~
+         unexpected
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/exception:109:8: note: 'unexpected' declared here
+  void unexpected() __attribute__ ((__noreturn__));
+       ^
+pure2-expected-is-as.cpp2:11:29: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<int>(ex1)) {
+                            ^~~
+                            exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:15:30: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<bool>(ex1)) {
+                             ^~~
+                             exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:20:30: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<void>(ex1)) {
+                             ^~~
+                             exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:25:29: warning: 'unexpected' is deprecated [-Wdeprecated-declarations]
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                            ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/exception:108:3: note: 'unexpected' has been explicitly marked deprecated here
+  _GLIBCXX11_DEPRECATED
+  ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/x86_64-linux-gnu/c++/12/bits/c++config.h:103:32: note: expanded from macro '_GLIBCXX11_DEPRECATED'
+# define _GLIBCXX11_DEPRECATED _GLIBCXX_DEPRECATED
+                               ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/x86_64-linux-gnu/c++/12/bits/c++config.h:94:46: note: expanded from macro '_GLIBCXX_DEPRECATED'
+# define _GLIBCXX_DEPRECATED __attribute__ ((__deprecated__))
+                                             ^
+pure2-expected-is-as.cpp2:25:29: error: 'unexpected' does not name a template but is followed by template arguments
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                            ^         ~~~~~
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/exception:109:8: note: non-template declaration found by name lookup
+  void unexpected() __attribute__ ((__noreturn__));
+       ^
+pure2-expected-is-as.cpp2:25:46: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                                             ^~~
+                                             exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:30:24: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is(ex1, 123)) {
+                       ^~~
+                       exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+pure2-expected-is-as.cpp2:34:24: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is(ex1, 100)) {
+                       ^~~
+                       exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+__MATHCALL_VEC (exp,, (_Mdouble_ __x));
+                ^
+In file included from pure2-expected-is-as.cpp:7:
+../../../include/cpp2util.h:1770:72: error: invalid application of 'sizeof' to a function type
+    (std::is_floating_point_v<From> && std::is_floating_point_v<To> && sizeof(From) > sizeof(To)) || // NOLINT(misc-redundant-expression)
+                                                                       ^~~~~~~~~~~~
+../../../include/cpp2util.h:2891:19: note: in instantiation of variable template specialization 'cpp2::impl::is_narrowing_v' requested here
+    if constexpr (is_narrowing_v<C, CPP2_TYPEOF(x)>) {
+                  ^
+pure2-expected-is-as.cpp2:39:28: note: in instantiation of function template specialization 'cpp2::impl::as_<int, double (&)(double) noexcept>' requested here
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+                           ^
+In file included from pure2-expected-is-as.cpp:7:
+../../../include/cpp2util.h:2892:9: error: static assertion failed due to requirement 'program_violates_type_safety_guarantee<int, double (double) noexcept>': 'as' does not allow unsafe possibly-lossy narrowing conversions - if you're sure you want this, use 'unchecked_narrow<T>' to explicitly force the conversion and possibly lose information
+        static_assert(
+        ^
+pure2-expected-is-as.cpp2:39:28: note: in instantiation of function template specialization 'cpp2::impl::as_<int, double (&)(double) noexcept>' requested here
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+                           ^
+In file included from pure2-expected-is-as.cpp:7:
+../../../include/cpp2util.h:2904:52: error: no matching function for call to 'as'
+    else if constexpr( std::is_same_v< CPP2_TYPEOF(as<C>(CPP2_FORWARD(x))), nonesuch_ > ) {
+                                                   ^~~~~
+../../../include/cpp2util.h:315:66: note: expanded from macro 'CPP2_TYPEOF'
+#define CPP2_TYPEOF(x)              std::remove_cvref_t<decltype(x)>
+                                                                 ^
+../../../include/cpp2util.h:1838:16: note: candidate template ignored: constraints not satisfied [with C = int, x:auto = double (&)(double) noexcept]
+constexpr auto as(auto&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+               ^
+../../../include/cpp2util.h:1844:18: note: because 'std::is_scalar_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+                (std::is_scalar_v<CPP2_TYPEOF(x)> && !std::is_enum_v<CPP2_TYPEOF(x)>)
+                 ^
+../../../include/cpp2util.h:1845:17: note: and 'std::is_floating_point_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+            ||  std::is_floating_point_v<CPP2_TYPEOF(x)>
+                ^
+../../../include/cpp2util.h:1846:17: note: and 'std::is_base_of_v<int, std::remove_cvref_t<decltype(x)> >' evaluated to false
+            ||  std::is_base_of_v<C, CPP2_TYPEOF(x)>
+                ^
+../../../include/cpp2util.h:1847:17: note: and 'std::is_base_of_v<std::remove_cvref_t<decltype(x)>, int>' evaluated to false
+            ||  std::is_base_of_v<CPP2_TYPEOF(x), C>
+                ^
+../../../include/cpp2util.h:1848:30: note: and 'C{std::forward<decltype(x)>(x)}' would be invalid: cannot initialize a value of type 'int' with an lvalue of type 'double (double) noexcept'
+            ||  requires { C{CPP2_FORWARD(x)}; }
+                             ^
+../../../include/cpp2util.h:325:37: note: expanded from macro 'CPP2_FORWARD'
+#define CPP2_FORWARD(x)             std::forward<decltype(x)>(x)
+                                    ^
+../../../include/cpp2util.h:1977:6: note: candidate template ignored: constraints not satisfied [with C = int, X = double (&)(double) noexcept]
+auto as(X&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+     ^
+../../../include/cpp2util.h:1976:23: note: because 'specialization_of_template<double (&)(double) noexcept, std::variant>' evaluated to false
+template< typename C, specialization_of_template<std::variant> X >
+                      ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+    { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      ^
+../../../include/cpp2util.h:2024:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+constexpr auto as( X && x ) -> decltype(auto) {
+               ^
+../../../include/cpp2util.h:2023:22: note: because 'same_type_as<double (&)(double) noexcept, std::any>' evaluated to false
+template<typename T, same_type_as<std::any> X>
+                     ^
+../../../include/cpp2util.h:754:24: note: because 'std::same_as<std::remove_cvref_t<double (&)(double) noexcept>, std::remove_cvref_t<any> >' evaluated to false
+concept same_type_as = std::same_as<std::remove_cvref_t<X>, std::remove_cvref_t<C>>;
+                       ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/concepts:63:9: note: because '__detail::__same_as<double (double) noexcept, std::any>' evaluated to false
+      = __detail::__same_as<_Tp, _Up> && __detail::__same_as<_Up, _Tp>;
+        ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/concepts:57:27: note: because 'std::is_same_v<double (double) noexcept, std::any>' evaluated to false
+      concept __same_as = std::is_same_v<_Tp, _Up>;
+                          ^
+../../../include/cpp2util.h:2069:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+constexpr auto as( X&& x ) -> decltype(auto) { 
+               ^
+../../../include/cpp2util.h:2068:22: note: because 'specialization_of_template<double (&)(double) noexcept, std::optional>' evaluated to false
+template<typename T, specialization_of_template<std::optional> X>
+                     ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+    { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      ^
+../../../include/cpp2util.h:1813:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+constexpr auto as() -> auto
+               ^
+../../../include/cpp2util.h:1824:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+constexpr auto as() -> auto
+               ^
+../../../include/cpp2util.h:2905:9: error: static assertion failed due to requirement 'program_violates_type_safety_guarantee<int, double (double) noexcept>': No safe 'as' cast available - please check your cast
+        static_assert(
+        ^
+../../../include/cpp2util.h:2911:12: error: no matching function for call to 'as'
+    return as<C>(CPP2_FORWARD(x));
+           ^~~~~
+../../../include/cpp2util.h:1838:16: note: candidate template ignored: constraints not satisfied [with C = int, x:auto = double (&)(double) noexcept]
+constexpr auto as(auto&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+               ^
+../../../include/cpp2util.h:1844:18: note: because 'std::is_scalar_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+                (std::is_scalar_v<CPP2_TYPEOF(x)> && !std::is_enum_v<CPP2_TYPEOF(x)>)
+                 ^
+../../../include/cpp2util.h:1845:17: note: and 'std::is_floating_point_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+            ||  std::is_floating_point_v<CPP2_TYPEOF(x)>
+                ^
+../../../include/cpp2util.h:1846:17: note: and 'std::is_base_of_v<int, std::remove_cvref_t<decltype(x)> >' evaluated to false
+            ||  std::is_base_of_v<C, CPP2_TYPEOF(x)>
+                ^
+../../../include/cpp2util.h:1847:17: note: and 'std::is_base_of_v<std::remove_cvref_t<decltype(x)>, int>' evaluated to false
+            ||  std::is_base_of_v<CPP2_TYPEOF(x), C>
+                ^
+../../../include/cpp2util.h:1848:30: note: and 'C{std::forward<decltype(x)>(x)}' would be invalid: cannot initialize a value of type 'int' with an lvalue of type 'double (double) noexcept'
+            ||  requires { C{CPP2_FORWARD(x)}; }
+                             ^
+../../../include/cpp2util.h:325:37: note: expanded from macro 'CPP2_FORWARD'
+#define CPP2_FORWARD(x)             std::forward<decltype(x)>(x)
+                                    ^
+../../../include/cpp2util.h:1977:6: note: candidate template ignored: constraints not satisfied [with C = int, X = double (&)(double) noexcept]
+auto as(X&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+     ^
+../../../include/cpp2util.h:1976:23: note: because 'specialization_of_template<double (&)(double) noexcept, std::variant>' evaluated to false
+template< typename C, specialization_of_template<std::variant> X >
+                      ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+    { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      ^
+../../../include/cpp2util.h:2024:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+constexpr auto as( X && x ) -> decltype(auto) {
+               ^
+../../../include/cpp2util.h:2023:22: note: because 'same_type_as<double (&)(double) noexcept, std::any>' evaluated to false
+template<typename T, same_type_as<std::any> X>
+                     ^
+../../../include/cpp2util.h:754:24: note: because 'std::same_as<std::remove_cvref_t<double (&)(double) noexcept>, std::remove_cvref_t<any> >' evaluated to false
+concept same_type_as = std::same_as<std::remove_cvref_t<X>, std::remove_cvref_t<C>>;
+                       ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/concepts:63:9: note: because '__detail::__same_as<double (double) noexcept, std::any>' evaluated to false
+      = __detail::__same_as<_Tp, _Up> && __detail::__same_as<_Up, _Tp>;
+        ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/concepts:57:27: note: because 'std::is_same_v<double (double) noexcept, std::any>' evaluated to false
+      concept __same_as = std::is_same_v<_Tp, _Up>;
+                          ^
+../../../include/cpp2util.h:2069:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+constexpr auto as( X&& x ) -> decltype(auto) { 
+               ^
+../../../include/cpp2util.h:2068:22: note: because 'specialization_of_template<double (&)(double) noexcept, std::optional>' evaluated to false
+template<typename T, specialization_of_template<std::optional> X>
+                     ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+    { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      ^
+../../../include/cpp2util.h:1813:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+constexpr auto as() -> auto
+               ^
+../../../include/cpp2util.h:1824:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+constexpr auto as() -> auto
+               ^
+pure2-expected-is-as.cpp2:39:37: error: use of undeclared identifier 'ex1'
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+                                    ^
+fatal error: too many errors emitted, stopping now [-ferror-limit=]
+1 warning and 20 errors generated.
diff --git a/regression-tests/test-results/clang-18-c++20/pure2-expected-is-as.cpp.output b/regression-tests/test-results/clang-18-c++20/pure2-expected-is-as.cpp.output
new file mode 100644
index 000000000..5c06a61b0
--- /dev/null
+++ b/regression-tests/test-results/clang-18-c++20/pure2-expected-is-as.cpp.output
@@ -0,0 +1,245 @@
+pure2-expected-is-as.cpp2:7:22: error: expected '(' for function-style cast or type construction
+    7 |     std::expected<int,int> ex1 {123}; 
+      |                   ~~~^
+pure2-expected-is-as.cpp2:7:10: error: no member named 'expected' in namespace 'std'; did you mean 'unexpected'?
+    7 |     std::expected<int,int> ex1 {123}; 
+      |     ~~~~~^~~~~~~~
+      |          unexpected
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/exception:110:8: note: 'unexpected' declared here
+  110 |   void unexpected() __attribute__ ((__noreturn__,__cold__));
+      |        ^
+pure2-expected-is-as.cpp2:8:22: error: expected '(' for function-style cast or type construction
+    8 |     std::expected<int,int> ex2 {std::unexpected(-1)}; 
+      |                   ~~~^
+pure2-expected-is-as.cpp2:8:10: error: no member named 'expected' in namespace 'std'; did you mean 'unexpected'?
+    8 |     std::expected<int,int> ex2 {std::unexpected(-1)}; 
+      |     ~~~~~^~~~~~~~
+      |          unexpected
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/exception:110:8: note: 'unexpected' declared here
+  110 |   void unexpected() __attribute__ ((__noreturn__,__cold__));
+      |        ^
+pure2-expected-is-as.cpp2:9:30: error: expected '(' for function-style cast or type construction
+    9 |     std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+      |                   ~~~~~~~~~~~^
+pure2-expected-is-as.cpp2:9:10: error: no member named 'expected' in namespace 'std'; did you mean 'unexpected'?
+    9 |     std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+      |     ~~~~~^~~~~~~~
+      |          unexpected
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/exception:110:8: note: 'unexpected' declared here
+  110 |   void unexpected() __attribute__ ((__noreturn__,__cold__));
+      |        ^
+pure2-expected-is-as.cpp2:11:29: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+   11 |     if (cpp2::impl::is<int>(ex1)) {
+      |                             ^~~
+      |                             exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+   95 | __MATHCALL_VEC (exp,, (_Mdouble_ __x));
+      |                 ^
+pure2-expected-is-as.cpp2:15:30: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+   15 |     if (cpp2::impl::is<bool>(ex1)) {
+      |                              ^~~
+      |                              exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+   95 | __MATHCALL_VEC (exp,, (_Mdouble_ __x));
+      |                 ^
+pure2-expected-is-as.cpp2:20:30: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+   20 |     if (cpp2::impl::is<void>(ex1)) {
+      |                              ^~~
+      |                              exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+   95 | __MATHCALL_VEC (exp,, (_Mdouble_ __x));
+      |                 ^
+pure2-expected-is-as.cpp2:25:29: warning: 'unexpected' is deprecated [-Wdeprecated-declarations]
+   25 |     if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+      |                             ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/exception:109:3: note: 'unexpected' has been explicitly marked deprecated here
+  109 |   _GLIBCXX11_DEPRECATED
+      |   ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/x86_64-linux-gnu/c++/14/bits/c++config.h:107:32: note: expanded from macro '_GLIBCXX11_DEPRECATED'
+  107 | # define _GLIBCXX11_DEPRECATED _GLIBCXX_DEPRECATED
+      |                                ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/x86_64-linux-gnu/c++/14/bits/c++config.h:98:46: note: expanded from macro '_GLIBCXX_DEPRECATED'
+   98 | # define _GLIBCXX_DEPRECATED __attribute__ ((__deprecated__))
+      |                                              ^
+pure2-expected-is-as.cpp2:25:29: error: 'unexpected' does not name a template but is followed by template arguments
+   25 |     if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+      |                             ^         ~~~~~
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/exception:110:8: note: non-template declaration found by name lookup
+  110 |   void unexpected() __attribute__ ((__noreturn__,__cold__));
+      |        ^
+pure2-expected-is-as.cpp2:25:46: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+   25 |     if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+      |                                              ^~~
+      |                                              exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+   95 | __MATHCALL_VEC (exp,, (_Mdouble_ __x));
+      |                 ^
+pure2-expected-is-as.cpp2:30:24: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+   30 |     if (cpp2::impl::is(ex1, 123)) {
+      |                        ^~~
+      |                        exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+   95 | __MATHCALL_VEC (exp,, (_Mdouble_ __x));
+      |                 ^
+pure2-expected-is-as.cpp2:34:24: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+   34 |     if (cpp2::impl::is(ex1, 100)) {
+      |                        ^~~
+      |                        exp
+/usr/include/x86_64-linux-gnu/bits/mathcalls.h:95:17: note: 'exp' declared here
+   95 | __MATHCALL_VEC (exp,, (_Mdouble_ __x));
+      |                 ^
+In file included from pure2-expected-is-as.cpp:7:
+../../../include/cpp2util.h:1770:72: error: invalid application of 'sizeof' to a function type
+ 1770 |     (std::is_floating_point_v<From> && std::is_floating_point_v<To> && sizeof(From) > sizeof(To)) || // NOLINT(misc-redundant-expression)
+      |                                                                        ^~~~~~~~~~~~
+../../../include/cpp2util.h:2891:19: note: in instantiation of variable template specialization 'cpp2::impl::is_narrowing_v' requested here
+ 2891 |     if constexpr (is_narrowing_v<C, CPP2_TYPEOF(x)>) {
+      |                   ^
+pure2-expected-is-as.cpp2:39:28: note: in instantiation of function template specialization 'cpp2::impl::as_<int, double (&)(double) noexcept>' requested here
+   39 |     auto val1 {cpp2::impl::as_<int>(ex1)}; 
+      |                            ^
+In file included from pure2-expected-is-as.cpp:7:
+../../../include/cpp2util.h:2893:13: error: static assertion failed due to requirement 'program_violates_type_safety_guarantee<int, double (double) noexcept>': 'as' does not allow unsafe possibly-lossy narrowing conversions - if you're sure you want this, use 'unchecked_narrow<T>' to explicitly force the conversion and possibly lose information
+ 2893 |             program_violates_type_safety_guarantee<C, CPP2_TYPEOF(x)>,
+      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+pure2-expected-is-as.cpp2:39:28: note: in instantiation of function template specialization 'cpp2::impl::as_<int, double (&)(double) noexcept>' requested here
+   39 |     auto val1 {cpp2::impl::as_<int>(ex1)}; 
+      |                            ^
+In file included from pure2-expected-is-as.cpp:7:
+../../../include/cpp2util.h:2904:52: error: no matching function for call to 'as'
+ 2904 |     else if constexpr( std::is_same_v< CPP2_TYPEOF(as<C>(CPP2_FORWARD(x))), nonesuch_ > ) {
+      |                                                    ^~~~~
+../../../include/cpp2util.h:315:66: note: expanded from macro 'CPP2_TYPEOF'
+  315 | #define CPP2_TYPEOF(x)              std::remove_cvref_t<decltype(x)>
+      |                                                                  ^
+../../../include/cpp2util.h:1838:16: note: candidate template ignored: constraints not satisfied [with C = int, x:auto = double (&)(double) noexcept]
+ 1838 | constexpr auto as(auto&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+      |                ^
+../../../include/cpp2util.h:1844:18: note: because 'std::is_scalar_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+ 1844 |                 (std::is_scalar_v<CPP2_TYPEOF(x)> && !std::is_enum_v<CPP2_TYPEOF(x)>)
+      |                  ^
+../../../include/cpp2util.h:1845:17: note: and 'std::is_floating_point_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+ 1845 |             ||  std::is_floating_point_v<CPP2_TYPEOF(x)>
+      |                 ^
+../../../include/cpp2util.h:1846:17: note: and 'std::is_base_of_v<int, std::remove_cvref_t<decltype(x)> >' evaluated to false
+ 1846 |             ||  std::is_base_of_v<C, CPP2_TYPEOF(x)>
+      |                 ^
+../../../include/cpp2util.h:1847:17: note: and 'std::is_base_of_v<std::remove_cvref_t<decltype(x)>, int>' evaluated to false
+ 1847 |             ||  std::is_base_of_v<CPP2_TYPEOF(x), C>
+      |                 ^
+../../../include/cpp2util.h:1848:30: note: and 'C{std::forward<decltype(x)>(x)}' would be invalid: cannot initialize a value of type 'int' with an lvalue of type 'double (double) noexcept'
+ 1848 |             ||  requires { C{CPP2_FORWARD(x)}; }
+      |                              ^
+../../../include/cpp2util.h:325:37: note: expanded from macro 'CPP2_FORWARD'
+  325 | #define CPP2_FORWARD(x)             std::forward<decltype(x)>(x)
+      |                                     ^
+../../../include/cpp2util.h:1977:6: note: candidate template ignored: constraints not satisfied [with C = int, X = double (&)(double) noexcept]
+ 1977 | auto as(X&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+      |      ^
+../../../include/cpp2util.h:1976:23: note: because 'specialization_of_template<double (&)(double) noexcept, std::variant>' evaluated to false
+ 1976 | template< typename C, specialization_of_template<std::variant> X >
+      |                       ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+  724 |     { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      |       ^
+../../../include/cpp2util.h:2024:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+ 2024 | constexpr auto as( X && x ) -> decltype(auto) {
+      |                ^
+../../../include/cpp2util.h:2023:22: note: because 'same_type_as<double (&)(double) noexcept, std::any>' evaluated to false
+ 2023 | template<typename T, same_type_as<std::any> X>
+      |                      ^
+../../../include/cpp2util.h:754:24: note: because 'std::same_as<std::remove_cvref_t<double (&)(double) noexcept>, std::remove_cvref_t<any> >' evaluated to false
+  754 | concept same_type_as = std::same_as<std::remove_cvref_t<X>, std::remove_cvref_t<C>>;
+      |                        ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/concepts:63:9: note: because '__detail::__same_as<double (double) noexcept, std::any>' evaluated to false
+   63 |       = __detail::__same_as<_Tp, _Up> && __detail::__same_as<_Up, _Tp>;
+      |         ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/concepts:57:27: note: because 'std::is_same_v<double (double) noexcept, std::any>' evaluated to false
+   57 |       concept __same_as = std::is_same_v<_Tp, _Up>;
+      |                           ^
+../../../include/cpp2util.h:2069:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+ 2069 | constexpr auto as( X&& x ) -> decltype(auto) { 
+      |                ^
+../../../include/cpp2util.h:2068:22: note: because 'specialization_of_template<double (&)(double) noexcept, std::optional>' evaluated to false
+ 2068 | template<typename T, specialization_of_template<std::optional> X>
+      |                      ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+  724 |     { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      |       ^
+../../../include/cpp2util.h:1813:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+ 1813 | constexpr auto as() -> auto
+      |                ^
+../../../include/cpp2util.h:1824:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+ 1824 | constexpr auto as() -> auto
+      |                ^
+../../../include/cpp2util.h:2906:13: error: static assertion failed due to requirement 'program_violates_type_safety_guarantee<int, double (double) noexcept>': No safe 'as' cast available - please check your cast
+ 2906 |             program_violates_type_safety_guarantee<C, CPP2_TYPEOF(x)>,
+      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+../../../include/cpp2util.h:2911:12: error: no matching function for call to 'as'
+ 2911 |     return as<C>(CPP2_FORWARD(x));
+      |            ^~~~~
+../../../include/cpp2util.h:1838:16: note: candidate template ignored: constraints not satisfied [with C = int, x:auto = double (&)(double) noexcept]
+ 1838 | constexpr auto as(auto&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+      |                ^
+../../../include/cpp2util.h:1844:18: note: because 'std::is_scalar_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+ 1844 |                 (std::is_scalar_v<CPP2_TYPEOF(x)> && !std::is_enum_v<CPP2_TYPEOF(x)>)
+      |                  ^
+../../../include/cpp2util.h:1845:17: note: and 'std::is_floating_point_v<std::remove_cvref_t<decltype(x)> >' evaluated to false
+ 1845 |             ||  std::is_floating_point_v<CPP2_TYPEOF(x)>
+      |                 ^
+../../../include/cpp2util.h:1846:17: note: and 'std::is_base_of_v<int, std::remove_cvref_t<decltype(x)> >' evaluated to false
+ 1846 |             ||  std::is_base_of_v<C, CPP2_TYPEOF(x)>
+      |                 ^
+../../../include/cpp2util.h:1847:17: note: and 'std::is_base_of_v<std::remove_cvref_t<decltype(x)>, int>' evaluated to false
+ 1847 |             ||  std::is_base_of_v<CPP2_TYPEOF(x), C>
+      |                 ^
+../../../include/cpp2util.h:1848:30: note: and 'C{std::forward<decltype(x)>(x)}' would be invalid: cannot initialize a value of type 'int' with an lvalue of type 'double (double) noexcept'
+ 1848 |             ||  requires { C{CPP2_FORWARD(x)}; }
+      |                              ^
+../../../include/cpp2util.h:325:37: note: expanded from macro 'CPP2_FORWARD'
+  325 | #define CPP2_FORWARD(x)             std::forward<decltype(x)>(x)
+      |                                     ^
+../../../include/cpp2util.h:1977:6: note: candidate template ignored: constraints not satisfied [with C = int, X = double (&)(double) noexcept]
+ 1977 | auto as(X&& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT_AS) -> decltype(auto)
+      |      ^
+../../../include/cpp2util.h:1976:23: note: because 'specialization_of_template<double (&)(double) noexcept, std::variant>' evaluated to false
+ 1976 | template< typename C, specialization_of_template<std::variant> X >
+      |                       ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+  724 |     { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      |       ^
+../../../include/cpp2util.h:2024:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+ 2024 | constexpr auto as( X && x ) -> decltype(auto) {
+      |                ^
+../../../include/cpp2util.h:2023:22: note: because 'same_type_as<double (&)(double) noexcept, std::any>' evaluated to false
+ 2023 | template<typename T, same_type_as<std::any> X>
+      |                      ^
+../../../include/cpp2util.h:754:24: note: because 'std::same_as<std::remove_cvref_t<double (&)(double) noexcept>, std::remove_cvref_t<any> >' evaluated to false
+  754 | concept same_type_as = std::same_as<std::remove_cvref_t<X>, std::remove_cvref_t<C>>;
+      |                        ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/concepts:63:9: note: because '__detail::__same_as<double (double) noexcept, std::any>' evaluated to false
+   63 |       = __detail::__same_as<_Tp, _Up> && __detail::__same_as<_Up, _Tp>;
+      |         ^
+/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/concepts:57:27: note: because 'std::is_same_v<double (double) noexcept, std::any>' evaluated to false
+   57 |       concept __same_as = std::is_same_v<_Tp, _Up>;
+      |                           ^
+../../../include/cpp2util.h:2069:16: note: candidate template ignored: constraints not satisfied [with T = int, X = double (&)(double) noexcept]
+ 2069 | constexpr auto as( X&& x ) -> decltype(auto) { 
+      |                ^
+../../../include/cpp2util.h:2068:22: note: because 'specialization_of_template<double (&)(double) noexcept, std::optional>' evaluated to false
+ 2068 | template<typename T, specialization_of_template<std::optional> X>
+      |                      ^
+../../../include/cpp2util.h:724:7: note: because 'specialization_of_template_helper<C>(std::forward<X>(x))' would be invalid: no matching function for call to 'specialization_of_template_helper'
+  724 |     { specialization_of_template_helper<C>(std::forward<X>(x)) } -> std::same_as<std::true_type>;
+      |       ^
+../../../include/cpp2util.h:1813:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+ 1813 | constexpr auto as() -> auto
+      |                ^
+../../../include/cpp2util.h:1824:16: note: candidate function template not viable: requires 0 arguments, but 1 was provided
+ 1824 | constexpr auto as() -> auto
+      |                ^
+pure2-expected-is-as.cpp2:39:37: error: use of undeclared identifier 'ex1'
+   39 |     auto val1 {cpp2::impl::as_<int>(ex1)}; 
+      |                                     ^
+fatal error: too many errors emitted, stopping now [-ferror-limit=]
+1 warning and 20 errors generated.
diff --git a/regression-tests/test-results/clang-18-c++23-libcpp/pure2-expected-is-as.cpp.execution b/regression-tests/test-results/clang-18-c++23-libcpp/pure2-expected-is-as.cpp.execution
new file mode 100644
index 000000000..5483d6cd7
--- /dev/null
+++ b/regression-tests/test-results/clang-18-c++23-libcpp/pure2-expected-is-as.cpp.execution
@@ -0,0 +1,15 @@
+ex1 is int
+ex1 is 123
+ex1 as int = 123
+ex2 is unexpected<int> and error is: -1
+ex2 is 'empty' aka unexpected<int> and error is: -1
+ex2 as std::unexpected<int> and error = -1
+
+expected<int, int> with value
+    ...integer 123
+
+expected<int, int> with unexpected
+    ...unexpected<int> -1
+
+expected<string, size_t> with value
+    ...string Expect the unexpected
diff --git a/regression-tests/test-results/gcc-10-c++20/pure2-expected-is-as.cpp.output b/regression-tests/test-results/gcc-10-c++20/pure2-expected-is-as.cpp.output
new file mode 100644
index 000000000..bce72f964
--- /dev/null
+++ b/regression-tests/test-results/gcc-10-c++20/pure2-expected-is-as.cpp.output
@@ -0,0 +1,39 @@
+pure2-expected-is-as.cpp2: In function ‘int main()’:
+pure2-expected-is-as.cpp2:7:10: error: ‘expected’ is not a member of ‘std’; did you mean ‘unexpected’?
+pure2-expected-is-as.cpp2:7:19: error: expected primary-expression before ‘int’
+pure2-expected-is-as.cpp2:8:10: error: ‘expected’ is not a member of ‘std’; did you mean ‘unexpected’?
+pure2-expected-is-as.cpp2:8:19: error: expected primary-expression before ‘int’
+pure2-expected-is-as.cpp2:9:10: error: ‘expected’ is not a member of ‘std’; did you mean ‘unexpected’?
+pure2-expected-is-as.cpp2:9:30: error: expected primary-expression before ‘,’ token
+pure2-expected-is-as.cpp2:9:37: error: expected primary-expression before ‘>’ token
+pure2-expected-is-as.cpp2:9:39: error: ‘ex3’ was not declared in this scope; did you mean ‘exp’?
+pure2-expected-is-as.cpp2:11:29: error: ‘ex1’ was not declared in this scope; did you mean ‘exp’?
+pure2-expected-is-as.cpp2:15:30: error: ‘ex1’ was not declared in this scope; did you mean ‘exp’?
+pure2-expected-is-as.cpp2:20:30: error: ‘ex1’ was not declared in this scope; did you mean ‘exp’?
+pure2-expected-is-as.cpp2:25:21: error: parse error in template argument list
+pure2-expected-is-as.cpp2:25:46: error: ‘ex1’ was not declared in this scope; did you mean ‘exp’?
+pure2-expected-is-as.cpp2:30:24: error: ‘ex1’ was not declared in this scope; did you mean ‘exp’?
+pure2-expected-is-as.cpp2:34:24: error: ‘ex1’ was not declared in this scope; did you mean ‘exp’?
+pure2-expected-is-as.cpp2:39:37: error: ‘ex1’ was not declared in this scope; did you mean ‘exp’?
+pure2-expected-is-as.cpp2:42:29: error: ‘ex2’ was not declared in this scope; did you mean ‘exp2’?
+pure2-expected-is-as.cpp2:47:30: error: ‘ex2’ was not declared in this scope; did you mean ‘exp2’?
+pure2-expected-is-as.cpp2:52:24: error: ‘ex2’ was not declared in this scope; did you mean ‘exp2’?
+pure2-expected-is-as.cpp2:57:21: error: parse error in template argument list
+pure2-expected-is-as.cpp2:57:46: error: ‘ex2’ was not declared in this scope; did you mean ‘exp2’?
+pure2-expected-is-as.cpp2:61:30: error: ‘ex2’ was not declared in this scope; did you mean ‘exp2’?
+pure2-expected-is-as.cpp2:65:31: error: parse error in template argument list
+pure2-expected-is-as.cpp2:65:57: error: ‘ex2’ was not declared in this scope; did you mean ‘exp2’?
+pure2-expected-is-as.cpp2: In function ‘void test_inspect(const auto:110&, const auto:111&)’:
+pure2-expected-is-as.cpp2:77:55: error: template argument 1 is invalid
+pure2-expected-is-as.cpp2:77:21: error: ‘cpp2::impl::unexp’ has not been declared
+pure2-expected-is-as.cpp2: In lambda function:
+pure2-expected-is-as.cpp2:78:33: error: ‘unexp’ was not declared in this scope
+pure2-expected-is-as.cpp2: In lambda function:
+pure2-expected-is-as.cpp2:85:34: error: parse error in template argument list
+pure2-expected-is-as.cpp2:85:159: error: parse error in template argument list
+In file included from pure2-expected-is-as.cpp:7:
+pure2-expected-is-as.cpp2:85:309: error: parse error in template argument list
+../../../include/cpp2util.h:315:66: note: in definition of macro ‘CPP2_TYPEOF’
+  315 | #define CPP2_TYPEOF(x)              std::remove_cvref_t<decltype(x)>
+      |                                                                  ^
+pure2-expected-is-as.cpp2:85:430: error: parse error in template argument list
diff --git a/regression-tests/test-results/gcc-13-c++2b/pure2-expected-is-as.cpp.execution b/regression-tests/test-results/gcc-13-c++2b/pure2-expected-is-as.cpp.execution
new file mode 100644
index 000000000..5483d6cd7
--- /dev/null
+++ b/regression-tests/test-results/gcc-13-c++2b/pure2-expected-is-as.cpp.execution
@@ -0,0 +1,15 @@
+ex1 is int
+ex1 is 123
+ex1 as int = 123
+ex2 is unexpected<int> and error is: -1
+ex2 is 'empty' aka unexpected<int> and error is: -1
+ex2 as std::unexpected<int> and error = -1
+
+expected<int, int> with value
+    ...integer 123
+
+expected<int, int> with unexpected
+    ...unexpected<int> -1
+
+expected<string, size_t> with value
+    ...string Expect the unexpected
diff --git a/regression-tests/test-results/gcc-14-c++2b/pure2-expected-is-as.cpp.execution b/regression-tests/test-results/gcc-14-c++2b/pure2-expected-is-as.cpp.execution
new file mode 100644
index 000000000..5483d6cd7
--- /dev/null
+++ b/regression-tests/test-results/gcc-14-c++2b/pure2-expected-is-as.cpp.execution
@@ -0,0 +1,15 @@
+ex1 is int
+ex1 is 123
+ex1 as int = 123
+ex2 is unexpected<int> and error is: -1
+ex2 is 'empty' aka unexpected<int> and error is: -1
+ex2 as std::unexpected<int> and error = -1
+
+expected<int, int> with value
+    ...integer 123
+
+expected<int, int> with unexpected
+    ...unexpected<int> -1
+
+expected<string, size_t> with value
+    ...string Expect the unexpected
diff --git a/regression-tests/test-results/msvc-2022-c++20/pure2-expected-is-as.cpp.output b/regression-tests/test-results/msvc-2022-c++20/pure2-expected-is-as.cpp.output
new file mode 100644
index 000000000..9b87b96a3
--- /dev/null
+++ b/regression-tests/test-results/msvc-2022-c++20/pure2-expected-is-as.cpp.output
@@ -0,0 +1,67 @@
+pure2-expected-is-as.cpp
+pure2-expected-is-as.cpp2(7): error C2039: 'expected': is not a member of 'std'
+predefined C++ types (compiler internal)(347): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(7): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(7): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(7): error C2143: syntax error: missing ';' before '}'
+pure2-expected-is-as.cpp2(8): error C2039: 'expected': is not a member of 'std'
+predefined C++ types (compiler internal)(347): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(8): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(8): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(8): error C2039: 'unexpected': is not a member of 'std'
+predefined C++ types (compiler internal)(347): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(8): error C2660: 'unexpected': function does not take 1 arguments
+C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.41.34120\include\eh.h(33): note: see declaration of 'unexpected'
+pure2-expected-is-as.cpp2(8): note: while trying to match the argument list '(int)'
+pure2-expected-is-as.cpp2(8): error C2143: syntax error: missing ';' before '}'
+pure2-expected-is-as.cpp2(9): error C2039: 'expected': is not a member of 'std'
+predefined C++ types (compiler internal)(347): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(9): error C2275: 'std::string': expected an expression instead of a type
+pure2-expected-is-as.cpp2(9): error C2065: 'ex3': undeclared identifier
+pure2-expected-is-as.cpp2(9): error C2275: 'size_t': expected an expression instead of a type
+pure2-expected-is-as.cpp2(11): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(15): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(20): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(25): error C2039: 'unexpected': is not a member of 'std'
+predefined C++ types (compiler internal)(347): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(25): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(25): error C2059: syntax error: '>'
+pure2-expected-is-as.cpp2(25): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(30): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(34): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(39): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(39): error C2119: 'val1': the type for 'auto' cannot be deduced from an empty initializer
+pure2-expected-is-as.cpp2(42): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(47): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(52): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(57): error C2039: 'unexpected': is not a member of 'std'
+predefined C++ types (compiler internal)(347): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(57): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(57): error C2059: syntax error: '>'
+pure2-expected-is-as.cpp2(57): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(58): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(61): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(62): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(65): error C2039: 'unexpected': is not a member of 'std'
+predefined C++ types (compiler internal)(347): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(65): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(65): error C2062: type 'unknown-type' unexpected
+pure2-expected-is-as.cpp2(65): error C2143: syntax error: missing ';' before '}'
+pure2-expected-is-as.cpp2(66): error C2143: syntax error: missing ';' before '<<'
+pure2-expected-is-as.cpp2(66): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
+pure2-expected-is-as.cpp2(66): error C2371: 'std::cout': redefinition; different basic types
+C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.41.34120\include\iostream(39): note: see declaration of 'std::cout'
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: '<<'
+pure2-expected-is-as.cpp2(66): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(66): error C2447: '{': missing function header (old-style formal list?)
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: '||'
+pure2-expected-is-as.cpp2(66): error C2065: 'Obj': undeclared identifier
+pure2-expected-is-as.cpp2(66): error C2065: 'Params': undeclared identifier
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: '}'
+pure2-expected-is-as.cpp2(66): error C2143: syntax error: missing ')' before ';'
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: 'requires'
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: ')'
+pure2-expected-is-as.cpp2(66): error C2065: 'obj': undeclared identifier
+pure2-expected-is-as.cpp2(66): error C3553: decltype expects an expression not a type
+pure2-expected-is-as.cpp2(66): error C2065: 'params': undeclared identifier
+pure2-expected-is-as.cpp2(66): fatal error C1003: error count exceeds 100; stopping compilation
diff --git a/regression-tests/test-results/msvc-2022-c++latest/pure2-expected-is-as.cpp.execution b/regression-tests/test-results/msvc-2022-c++latest/pure2-expected-is-as.cpp.execution
new file mode 100644
index 000000000..5483d6cd7
--- /dev/null
+++ b/regression-tests/test-results/msvc-2022-c++latest/pure2-expected-is-as.cpp.execution
@@ -0,0 +1,15 @@
+ex1 is int
+ex1 is 123
+ex1 as int = 123
+ex2 is unexpected<int> and error is: -1
+ex2 is 'empty' aka unexpected<int> and error is: -1
+ex2 as std::unexpected<int> and error = -1
+
+expected<int, int> with value
+    ...integer 123
+
+expected<int, int> with unexpected
+    ...unexpected<int> -1
+
+expected<string, size_t> with value
+    ...string Expect the unexpected
diff --git a/regression-tests/test-results/msvc-2022-c++latest/pure2-expected-is-as.cpp.output b/regression-tests/test-results/msvc-2022-c++latest/pure2-expected-is-as.cpp.output
new file mode 100644
index 000000000..6e7839bd6
--- /dev/null
+++ b/regression-tests/test-results/msvc-2022-c++latest/pure2-expected-is-as.cpp.output
@@ -0,0 +1 @@
+pure2-expected-is-as.cpp
diff --git a/regression-tests/test-results/pure2-expected-is-as.cpp b/regression-tests/test-results/pure2-expected-is-as.cpp
new file mode 100644
index 000000000..956d9547e
--- /dev/null
+++ b/regression-tests/test-results/pure2-expected-is-as.cpp
@@ -0,0 +1,117 @@
+
+#define CPP2_IMPORT_STD          Yes
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+#line 1 "pure2-expected-is-as.cpp2"
+
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+#line 1 "pure2-expected-is-as.cpp2"
+// `std::expected` requires C++23 so a dedicated test file is needed
+// since only MSVC supports it at time of writing, and there's no #ifdef
+// or `static if` support in Cpp2 (yet?).
+
+#line 5 "pure2-expected-is-as.cpp2"
+[[nodiscard]] auto main() -> int;
+
+#line 75 "pure2-expected-is-as.cpp2"
+auto test_inspect(auto const& x, auto const& msg) -> void;
+
+//=== Cpp2 function definitions =================================================
+
+#line 1 "pure2-expected-is-as.cpp2"
+
+#line 5 "pure2-expected-is-as.cpp2"
+[[nodiscard]] auto main() -> int{
+
+    std::expected<int,int> ex1 {123}; 
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+
+    if (cpp2::impl::is<int>(ex1)) {
+        std::cout << "ex1 is int\n";
+    }
+
+    if (cpp2::impl::is<bool>(ex1)) {
+        std::cout << "BUG - ex1 is not a bool\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is<void>(ex1)) {
+        std::cout << "BUG - ex1 is not 'empty'\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+        std::cout << "BUG - ex1 is not unexpected\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is(ex1, 123)) {
+        std::cout << "ex1 is 123\n";
+    }
+
+    if (cpp2::impl::is(ex1, 100)) {
+        std::cout << "BUG - ex1's value is not 100\n";
+        return -1; 
+    }
+
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+    std::cout << "ex1 as int = " << cpp2::move(val1) << "\n";
+
+    if (cpp2::impl::is<int>(ex2)) {
+        std::cout << "BUG - ex2 is not an int\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is<bool>(ex2)) {
+        std::cout << "BUG - ex2 is not a bool\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is(ex2, 123)) {
+        std::cout << "BUG - ex2 does not have a value\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is<std::unexpected<int>>(ex2)) {
+        std::cout << "ex2 is unexpected<int> and error is: " << CPP2_UFCS(error)(ex2) << "\n";
+    }
+
+    if (cpp2::impl::is<void>(ex2)) {
+        std::cout << "ex2 is 'empty' aka unexpected<int> and error is: " << CPP2_UFCS(error)(ex2) << "\n";
+    }
+
+    auto ex2_err {cpp2::impl::as_<std::unexpected<int>>(ex2)}; 
+    std::cout << "ex2 as std::unexpected<int> and error = " << CPP2_UFCS(error)(cpp2::move(ex2_err)) << "\n";
+
+    test_inspect(cpp2::move(ex1), "expected<int, int> with value");
+    test_inspect(cpp2::move(ex2), "expected<int, int> with unexpected");
+    test_inspect(cpp2::move(ex3), "expected<string, size_t> with value");
+
+    return 0; 
+}
+
+#line 75 "pure2-expected-is-as.cpp2"
+auto test_inspect(auto const& x, auto const& msg) -> void{
+
+    auto unwrap {[](cpp2::impl::in<std::unexpected<int>> unexp) -> auto{
+        return CPP2_UFCS(error)(unexp); 
+    }}; 
+
+    std::cout 
+        << "\n" << msg << "\n    ..." 
+        << [&] () -> std::string { auto&& _expr = x;
+            if (cpp2::impl::is<int>(_expr)) { if constexpr( requires{"integer " + std::to_string(cpp2::impl::as<int>(x));} ) if constexpr( std::is_convertible_v<CPP2_TYPEOF(("integer " + std::to_string(cpp2::impl::as<int>(x)))),std::string> ) return "integer " + std::to_string(cpp2::impl::as<int>(x)); else return std::string{}; else return std::string{}; }
+            else if (cpp2::impl::is<std::unexpected<int>>(_expr)) { if constexpr( requires{"unexpected<int> " + std::to_string(cpp2::move(unwrap)(cpp2::impl::as<std::unexpected<int>>(x)));} ) if constexpr( std::is_convertible_v<CPP2_TYPEOF(("unexpected<int> " + std::to_string(cpp2::move(unwrap)(cpp2::impl::as<std::unexpected<int>>(x))))),std::string> ) return "unexpected<int> " + std::to_string(cpp2::move(unwrap)(cpp2::impl::as<std::unexpected<int>>(x))); else return std::string{}; else return std::string{}; }
+            else if (cpp2::impl::is<std::string>(_expr)) { if constexpr( requires{"string " + cpp2::impl::as<std::string>(x);} ) if constexpr( std::is_convertible_v<CPP2_TYPEOF(("string " + cpp2::impl::as<std::string>(x))),std::string> ) return "string " + cpp2::impl::as<std::string>(x); else return std::string{}; else return std::string{}; }
+            else return " no match"; }
+        () 
+        << "\n";
+}
+
diff --git a/regression-tests/test-results/pure2-expected-is-as.cpp2.output b/regression-tests/test-results/pure2-expected-is-as.cpp2.output
new file mode 100644
index 000000000..a63d2c2a1
--- /dev/null
+++ b/regression-tests/test-results/pure2-expected-is-as.cpp2.output
@@ -0,0 +1,2 @@
+pure2-expected-is-as.cpp2... ok (all Cpp2, passes safety checks)
+