diff --git a/CMakeLists.txt b/CMakeLists.txt
index 253952e6..d7add659 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -199,6 +199,8 @@ list (
     coord/simd_neon.hpp
     coord/store.hpp
     coord/traits.hpp
+    cpp.cpp
+    cpp.hpp
     cpuid.cpp
     cpuid.hpp
     cpuid_x86.cpp
@@ -551,6 +553,10 @@ if (TESTS)
         target_include_directories(util_${name} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
         add_test(NAME util_${name} COMMAND util_${name})
     endforeach(t)
+
+    configure_file (test/cpp.sh.in util_test_cpp.sh @ONLY)
+    add_test (NAME util_test_cpp COMMAND util_test_cpp.sh)
+    set_property (TEST util_test_cpp APPEND PROPERTY DEPENDS util_macro)
 endif ()
 
 
diff --git a/cpp.cpp b/cpp.cpp
new file mode 100644
index 00000000..a9660668
--- /dev/null
+++ b/cpp.cpp
@@ -0,0 +1,171 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2018 Danny Robson <danny@nerdcruft.net>
+ */
+
+
+///////////////////////////////////////////////////////////////////////////////
+#include "cpp.hpp"
+
+#include "io.hpp"
+#include "cast.hpp"
+
+using util::cpp::include;
+using util::cpp::passthrough;
+using util::cpp::processor;
+
+
+///////////////////////////////////////////////////////////////////////////////
+processor::processor ()
+{
+    m_directives.insert ({
+        "include",
+        std::make_unique<include> (*this)
+    });
+}
+
+
+//-----------------------------------------------------------------------------
+void
+processor::add (std::string token, std::unique_ptr<directive> handler)
+{
+    m_directives.emplace (std::pair {std::move (token), std::move (handler)});
+};
+
+
+//-----------------------------------------------------------------------------
+void
+processor::process (std::ostream &os, const std::experimental::filesystem::path &src) const
+{
+    const auto data = util::slurp<char> (src);
+    context ctx;
+    ctx.source.push (src);
+
+    util::tokeniser<const char*> tok (data, '\n');
+    process (os, ctx, util::view (tok.begin (), tok.end ()));
+}
+
+
+//-----------------------------------------------------------------------------
+util::tokeniser<const char*>::iterator
+processor::process (
+    std::ostream &os,
+    context &ctx,
+    util::view<util::tokeniser<const char*>::iterator> lines) const
+{
+    for (auto l = lines.begin (), last = lines.end (); l != last; ++l) {
+        if (l->empty () || (*l)[0] != '#') {
+            os << *l << '\n';
+            continue;
+        }
+
+        auto tokens = util::tokeniser (*l, ' ');
+        auto head = tokens.begin ();
+        auto head_string = std::string { head->begin () + 1, head->size () - 1 };
+
+        if (*head == "#endif")
+            return l;
+
+
+        if (*head == "#define") {
+            auto key = head;
+            ++key;
+
+            if (key == tokens.end ())
+                throw std::runtime_error ("expected token for define");
+
+            std::string key_string { key->begin (), key->size () };
+
+            auto val = key;
+            ++val;
+            ctx.defines[key_string] = val == tokens.end () ? "" : std::string (val->begin (), val->size ());
+            continue;
+        }
+
+        if (*head == "#ifndef") {
+            auto tail = head + 1;
+            if (tail == tokens.end ())
+                throw std::runtime_error ("expected token for define");
+
+            // recurse and parse the block...
+            std::string name { tail->begin (), tail->end () };
+            if (ctx.defines.find (name) == ctx.defines.cend ()) {
+                l = process (os, ctx, {++l, lines.end ()});
+            // ... or skip until and endif
+            } else {
+                for (++l; l != lines.end () && *l != "#endif"; ++l)
+                    ;
+            }
+
+            // check if we've got the expected endif
+            if (l == lines.cend () || *l != "#endif")
+                throw std::runtime_error ("expected #endif");
+
+            continue;
+        }
+
+        auto handler = m_directives.find (head_string);
+        if (handler == m_directives.end ())
+            throw unknown_directive (head_string);
+
+        lines.consume (handler->second->process (os, ctx, {l, lines.end()}));
+    }
+
+    return lines.end ();
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+passthrough::passthrough (const std::string &name):
+    m_name (name)
+{ ; }
+
+
+//-----------------------------------------------------------------------------
+util::tokeniser<const char*>::iterator
+passthrough::process (std::ostream &os,
+                      context&,
+                      util::view<util::tokeniser<const char*>::iterator> lines) const
+{
+    os << *lines.begin () << '\n';
+    return lines.begin ()++;
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+include::include (processor &_parent):
+    m_parent (_parent)
+{ ; }
+
+
+//-----------------------------------------------------------------------------
+util::tokeniser<const char*>::iterator
+include::process (std::ostream &os,
+                  context &ctx,
+                  util::view<util::tokeniser<const char*>::iterator> lines) const
+{
+    const auto name = lines.begin ()->slice (strlen("#include '"), -2);
+    std::experimental::filesystem::path fragment { name.begin (), name.end () };
+
+    const auto target = ctx.source.top ().parent_path () / fragment;
+    const auto data = util::slurp<char> (target);
+
+    ctx.source.push (target);
+    util::tokeniser<const char*> tok (data, '\n');
+    m_parent.process (os, ctx, util::view (tok.begin (), tok.end ()));
+
+    ctx.source.pop ();
+
+    return lines.begin ()++;
+}
diff --git a/cpp.hpp b/cpp.hpp
new file mode 100644
index 00000000..6ac99b76
--- /dev/null
+++ b/cpp.hpp
@@ -0,0 +1,119 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2018 Danny Robson <danny@nerdcruft.net>
+ */
+
+#ifndef CRUFT_UTIL_CPP_HPP
+#define CRUFT_UTIL_CPP_HPP
+
+#include "string.hpp"
+#include "view.hpp"
+
+#include <experimental/filesystem>
+#include <string>
+#include <map>
+#include <stdexcept>
+#include <stack>
+
+namespace util::cpp {
+    ///////////////////////////////////////////////////////////////////////////
+    struct context {
+        std::stack<std::experimental::filesystem::path> source;
+        std::map<std::string,std::string> defines;
+    };
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    class directive {
+    public:
+        virtual ~directive () = default;
+
+        virtual util::tokeniser<const char*>::iterator
+        process (std::ostream&,
+                 context&,
+                 util::view<util::tokeniser<const char*>::iterator>) const = 0;
+    };
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    class processor {
+    public:
+        processor ();
+        void add (std::string token, std::unique_ptr<directive>);
+
+        void process (std::ostream&, const std::experimental::filesystem::path&) const;
+
+        std::experimental::filesystem::path
+        resolve (const std::experimental::filesystem::path&) const;
+
+        util::tokeniser<const char*>::iterator
+        process (std::ostream&,
+                 context&,
+                 util::view<util::tokeniser<const char*>::iterator>) const;
+
+    private:
+        std::map<std::string, std::unique_ptr<directive>> m_directives;
+    };
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    class unknown_directive : public std::runtime_error {
+        using runtime_error::runtime_error;
+    };
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    class ignore final : public directive {
+        virtual util::tokeniser<const char*>::iterator
+        process (std::ostream&,
+                 context&,
+                 util::view<util::tokeniser<const char*>::iterator> lines) const override
+        { return lines.begin ()++; }
+    };
+
+
+    //-------------------------------------------------------------------------
+    class passthrough final : public directive {
+    public:
+        passthrough (const std::string &name);
+
+        virtual util::tokeniser<const char*>::iterator
+        process (std::ostream&,
+                 context&,
+                 util::view<util::tokeniser<const char*>::iterator>) const override;
+
+    private:
+        const std::string m_name;
+    };
+
+
+    //-------------------------------------------------------------------------
+    class include : public directive {
+    public:
+        include (processor &_parent);
+
+        void add (const std::experimental::filesystem::path&);
+
+        virtual util::tokeniser<const char*>::iterator
+        process (std::ostream&,
+                 context&,
+                 util::view<util::tokeniser<const char*>::iterator>) const override;
+
+    private:
+        processor &m_parent;
+        std::vector<std::experimental::filesystem::path> m_paths;
+    };
+};
+
+#endif
diff --git a/test/cpp.sh.in b/test/cpp.sh.in
new file mode 100755
index 00000000..88bf6e3b
--- /dev/null
+++ b/test/cpp.sh.in
@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+
+CPP="@CMAKE_CURRENT_BINARY_DIR@/macro"
+
+count=0
+ret=0
+
+for src in "@CMAKE_CURRENT_SOURCE_DIR@/test/cpp/good"/*.inc; do
+    res="${src%.inc}.res"
+
+    if cmp --quiet <($CPP ${src}) <(cat ${res}); then
+        head="ok"
+    else
+        head="not ok"
+        ret=1
+    fi
+
+    echo "${head} - ${src}"
+    count=$((count+1))
+done
+
+echo "1..${count}"
+exit $ret
diff --git a/test/cpp/good/0000_empty.inc b/test/cpp/good/0000_empty.inc
new file mode 100644
index 00000000..e69de29b
diff --git a/test/cpp/good/0000_empty.res b/test/cpp/good/0000_empty.res
new file mode 100644
index 00000000..e69de29b
diff --git a/test/cpp/good/0001_one_word.inc b/test/cpp/good/0001_one_word.inc
new file mode 100644
index 00000000..257cc564
--- /dev/null
+++ b/test/cpp/good/0001_one_word.inc
@@ -0,0 +1 @@
+foo
diff --git a/test/cpp/good/0001_one_word.res b/test/cpp/good/0001_one_word.res
new file mode 100644
index 00000000..257cc564
--- /dev/null
+++ b/test/cpp/good/0001_one_word.res
@@ -0,0 +1 @@
+foo
diff --git a/test/cpp/good/1000_relative_include.inc b/test/cpp/good/1000_relative_include.inc
new file mode 100644
index 00000000..4b7bf801
--- /dev/null
+++ b/test/cpp/good/1000_relative_include.inc
@@ -0,0 +1 @@
+#include "0000_empty.inc"
diff --git a/test/cpp/good/1000_relative_include.res b/test/cpp/good/1000_relative_include.res
new file mode 100644
index 00000000..e69de29b
diff --git a/test/cpp/good/2000_header_guard.inc b/test/cpp/good/2000_header_guard.inc
new file mode 100644
index 00000000..4501a2e1
--- /dev/null
+++ b/test/cpp/good/2000_header_guard.inc
@@ -0,0 +1,2 @@
+#include "guarded.hpp"
+#include "guarded.hpp"
diff --git a/test/cpp/good/2000_header_guard.res b/test/cpp/good/2000_header_guard.res
new file mode 100644
index 00000000..ba578e48
--- /dev/null
+++ b/test/cpp/good/2000_header_guard.res
@@ -0,0 +1 @@
+BAR
diff --git a/test/cpp/good/guarded.hpp b/test/cpp/good/guarded.hpp
new file mode 100644
index 00000000..5930c806
--- /dev/null
+++ b/test/cpp/good/guarded.hpp
@@ -0,0 +1,4 @@
+#ifndef FOO
+#define FOO
+BAR
+#endif
diff --git a/tools/macro.cpp b/tools/macro.cpp
index 78890c7e..01306569 100644
--- a/tools/macro.cpp
+++ b/tools/macro.cpp
@@ -2,6 +2,7 @@
 #include "iterator.hpp"
 #include "string.hpp"
 #include "view.hpp"
+#include "cpp.hpp"
 
 #include <iostream>
 #include <cstdlib>
@@ -17,6 +18,7 @@ enum {
 };
 
 
+#if 0
 ///////////////////////////////////////////////////////////////////////////////
 void process (std::ostream &dst, const std::experimental::filesystem::path&);
 
@@ -74,4 +76,19 @@ main (const int argc, const char **argv)
     } else {
         process (std::cout, src);
     };
-};
\ No newline at end of file
+};
+
+#endif
+
+
+int
+main (const int argc, const char **argv)
+{
+    if (argc < 2) {
+        std::cerr << argv[ARG_SELF] <<  " <src>\n";
+        return EXIT_FAILURE;
+    }
+
+    util::cpp::processor cpp;
+    cpp.process (std::cout, argv[ARG_SRC]);
+}
\ No newline at end of file