diff --git a/tools/spec.py b/tools/spec.py
index 51e8f58..7009af3 100644
--- a/tools/spec.py
+++ b/tools/spec.py
@@ -715,6 +715,171 @@ def parse_extensions(reg:registry, root):
         reg.extensions[name] = extension(node)
 
 
+###############################################################################
+def write_header(path:str, q):
+    with open(path, 'w') as dst:
+        dst.write("#pragma once\n")
+
+        # Write the declarations and definitions for all types.
+        for obj in q:
+            dst.write(obj.declare())
+            dst.write('\n')
+            dst.write(obj.define(reg))
+            dst.write('\n')
+
+
+        # Define the default case for device and instance type traits.
+        dst.write("""
+        #include <type_traits>
+
+        /// A type trait that tests if a Vulkan type is an instance type
+        template <typename NativeT>
+        struct is_instance:
+            public std::false_type
+        {};
+
+
+        /// A type trait that tests if a Vulkan type is a device type
+        template <typename NativeT>
+        struct is_device:
+            public std::false_type
+        {};
+
+
+        template <typename T>
+        constexpr auto is_instance_v = is_instance<T>::value;
+
+        template <typename T>
+        constexpr auto is_device_v = is_device<T>::value;
+        """)
+
+        # Specialise traits for device and instance types.
+        for obj in q:
+            if not isinstance(obj,handle):
+                continue
+
+            device_value = "true_type" if obj.has_parent("VkDevice", reg) else "false_type"
+            instance_value = "true_type" if obj.has_parent("VkInstance", reg) else "false_type"
+
+            dst.write(f"""
+            template <> struct is_instance<{obj.name}>: public std::{instance_value} {{ }};
+            template <> struct is_device<{obj.name}>: public std::{device_value} {{ }};
+            """)
+
+
+##-----------------------------------------------------------------------------
+def write_icd(path:str, q):
+    with open(path, 'w') as icd:
+        commands = [i for i in q if isinstance(i, command)]
+        instance_commands = [i for i in commands if i.is_instance(reg)]
+        device_commands = [i for i in commands if i.is_device(reg)]
+
+        assert len(instance_commands) + len(device_commands) == len(commands)
+
+        icd.write(f"""
+        #include "vk.hpp"
+
+        #include <cruft/util/preprocessor.hpp>
+
+        #define MAP_COMMANDS(FUNC) MAP0(FUNC,{",".join(i.name for i in commands)})
+        #define MAP_INSTANCE_COMMANDS(FUNC) MAP0(FUNC,{",".join(i.name for i in instance_commands)})
+        #define MAP_DEVICE_COMMANDS(FUNC) MAP0(FUNC,{",".join(i.name for i in device_commands)})
+
+        namespace cruft::vk::icd {{
+        class vendor;
+
+        struct func {{
+            void *handle;
+            void const *table;
+        }};
+
+        struct instance_table {{
+            instance_table (vendor &);
+        """)
+
+        for obj in instance_commands:
+            icd.write(f"{obj.result} (*{obj.name}) ({','.join(p.param for p in obj.params)}) = nullptr;\n")
+
+        icd.write("""};
+
+        struct device_table {
+        """)
+
+        for obj in device_commands:
+            icd.write(f"{obj.result} (*{obj.name}) ({','.join(p.param for p in obj.params)}) = nullptr;\n")
+
+        icd.write("""
+        };
+        }
+        """)
+
+
+##-----------------------------------------------------------------------------
+def write_dispatch(path:str, q):
+    with open(path, 'w') as dispatch:
+        dispatch.write("""
+        #include "../vk.hpp"
+        #include "vtable.hpp"
+
+        #include "icd/dispatch.hpp"
+
+        #include <cruft/util/debug.hpp>
+
+        #pragma GCC diagnostic ignored "-Wunused-parameter"
+
+        static cruft::vk::icd::instance_table const *i_table [[maybe_unused]] = nullptr;
+        static cruft::vk::icd::device_table const *d_table [[maybe_unused]] = nullptr;
+
+        void (*cruft_vk_icdGetInstanceProcAddr) (
+            VkInstance instance,
+            const char* pName
+        ) = nullptr;
+
+        void cruft::vk::icd::init (vendor const &impl)
+        {
+            cruft_vk_icdGetInstanceProcAddr = impl.vtable.GetInstanceProc;
+        }
+
+        """)
+
+        for obj in (i for i in q if isinstance(i, command)):
+            first_arg = reg.types[obj.params[0].type]
+
+            if not isinstance(first_arg, handle):
+                dispatch.write(f"""
+                extern "C" {obj.result} {rename(obj.name)} ({", ".join(p.param for p in obj.params)}) noexcept {{
+                    unimplemented ();
+                }}""")
+                continue
+
+            if first_arg.has_parent('VkDevice', reg):
+                table = "d_table";
+            elif first_arg.has_parent('VkInstance', reg):
+                table = 'i_table'
+            else:
+                raise Exception("Unknown param type")
+
+
+            dispatch.write(f"""
+            extern "C" {obj.result} {rename(obj.name)} ({", ".join(p.param for p in obj.params)}) noexcept {{
+                using first_arg_t = std::decay_t<decltype({obj.params[0].name})>;
+
+                if constexpr (is_instance_v<first_arg_t>) {{
+                    auto const entry = reinterpret_cast<cruft::vk::icd::func const*> ({obj.params[0].name});
+                    auto const *table = reinterpret_cast<decltype({table})> (entry->table);
+
+                    return (table->{obj.name})(
+                        reinterpret_cast<decltype({obj.params[0].name})> (entry->handle)
+                        {", ".join([''] + [p.name for p in obj.params[1:]])}
+                    );
+                }} else {{
+                    unimplemented ();
+                }}
+            }}
+            """)
+
+
+
 ###############################################################################
 def enqueue_type(name:str, queued:Set[str], types:Dict[str,type]):
     if name in queued:
@@ -784,151 +949,6 @@ if __name__ == '__main__':
     extensions = ["VK_KHR_swapchain", "VK_EXT_debug_report", "VK_KHR_external_memory"]
     q = reg.serialise(args.platform)
 
-    with open(args.dst, 'w') as dst:
-        dst.write("#pragma once\n")
-        for obj in q:
-            dst.write(obj.declare())
-            dst.write('\n')
-            dst.write(obj.define(reg))
-            dst.write('\n')
-
-
-        dst.write("""
-        #include <type_traits>
-
-        template <typename NativeT>
-        struct is_instance:
-            public std::false_type
-        {};
-
-        template <typename NativeT>
-        struct is_device:
-            public std::false_type
-        {};
-
-
-        template <typename T>
-        constexpr auto is_instance_v = is_instance<T>::value;
-
-        template <typename T>
-        constexpr auto is_device_v = is_device<T>::value;
-        """)
-
-        for obj in q:
-            if not isinstance(obj,handle):
-                continue
-
-            device_value = "true_type" if obj.has_parent("VkDevice", reg) else "false_type"
-            instance_value = "true_type" if obj.has_parent("VkInstance", reg) else "false_type"
-
-            dst.write(f"""
-            template <> struct is_instance<{obj.name}>: public std::{instance_value} {{ }};
-            template <> struct is_device<{obj.name}>: public std::{device_value} {{ }};
-            """)
-
-    with open(args.icd, 'w') as icd:
-        commands = [i for i in q if isinstance(i, command)]
-        instance_commands = [i for i in commands if i.is_instance(reg)]
-        device_commands = [i for i in commands if i.is_device(reg)]
-
-        assert len(instance_commands) + len(device_commands) == len(commands)
-
-        icd.write(f"""
-        #include "vk.hpp"
-
-        #include <cruft/util/preprocessor.hpp>
-
-        #define MAP_COMMANDS(FUNC) MAP0(FUNC,{",".join(i.name for i in commands)})
-        #define MAP_INSTANCE_COMMANDS(FUNC) MAP0(FUNC,{",".join(i.name for i in instance_commands)})
-        #define MAP_DEVICE_COMMANDS(FUNC) MAP0(FUNC,{",".join(i.name for i in device_commands)})
-
-        namespace cruft::vk::icd {{
-        class vendor;
-
-        struct func {{
-            void *handle;
-            void const *table;
-        }};
-
-        struct instance_table {{
-            instance_table (vendor &);
-        """)
-
-        for obj in instance_commands:
-            icd.write(f"{obj.result} (*{obj.name}) ({','.join(p.param for p in obj.params)}) = nullptr;\n")
-
-        icd.write("""};
-
-        struct device_table {
-        """)
-
-        for obj in device_commands:
-            icd.write(f"{obj.result} (*{obj.name}) ({','.join(p.param for p in obj.params)}) = nullptr;\n")
-
-        icd.write("""
-        };
-        }
-        """)
-
-
-    with open(args.dispatch, 'w') as dispatch:
-        dispatch.write("""
-        #include "../vk.hpp"
-        #include "vtable.hpp"
-
-        #include "icd/dispatch.hpp"
-
-        #include <cruft/util/debug.hpp>
-
-        #pragma GCC diagnostic ignored "-Wunused-parameter"
-
-        static cruft::vk::icd::instance_table const *i_table [[maybe_unused]] = nullptr;
-        static cruft::vk::icd::device_table const *d_table [[maybe_unused]] = nullptr;
-
-        void (*cruft_vk_icdGetInstanceProcAddr) (
-            VkInstance instance,
-            const char* pName
-        ) = nullptr;
-
-        void cruft::vk::icd::init (vendor const &impl)
-        {
-            cruft_vk_icdGetInstanceProcAddr = impl.vtable.GetInstanceProc;
-        }
-
-        """)
-
-        for obj in commands:
-            first_arg = reg.types[obj.params[0].type]
-
-            if not isinstance(first_arg, handle):
-                dispatch.write(f"""
-                extern "C" {obj.result} {rename(obj.name)} ({", ".join(p.param for p in obj.params)}) noexcept {{
-                    unimplemented ();
-                }}""")
-                continue
-
-            if first_arg.has_parent('VkDevice', reg):
-                table = "d_table";
-            elif first_arg.has_parent('VkInstance', reg):
-                table = 'i_table'
-            else:
-                raise Exception("Unknown param type")
-
-
-            dispatch.write(f"""
-            extern "C" {obj.result} {rename(obj.name)} ({", ".join(p.param for p in obj.params)}) noexcept {{
-                using first_arg_t = std::decay_t<decltype({obj.params[0].name})>;
-
-                if constexpr (is_instance_v<first_arg_t>) {{
-                    auto const entry = reinterpret_cast<cruft::vk::icd::func const*> ({obj.params[0].name});
-                    auto const *table = reinterpret_cast<decltype({table})> (entry->table);
-
-                    return (table->{obj.name})(
-                        reinterpret_cast<decltype({obj.params[0].name})> (entry->handle)
-                        {", ".join([''] + [p.name for p in obj.params[1:]])}
-                    );
-                }} else {{
-                    unimplemented ();
-                }}
-            }}
-            """)
+    write_header(args.dst, q)
+    write_icd(args.icd, q)
+    write_dispatch(args.dispatch, q)