diff --git a/Makefile b/Makefile
index 5f92fce..6354096 100644
--- a/Makefile
+++ b/Makefile
@@ -239,107 +239,96 @@ sanity_test_web: $(WEB)/ueforth.js
 $(GEN):
 	mkdir -p $@
 
-$(GEN)/posix_boot_merged.fs: posix/posix_boot.fs | $(GEN)
+$(GEN)/posix_boot.h: posix/posix_boot.fs | $(GEN)
 	./tools/importation.py $< $@ \
-    -I . -I $(GEN) --depsout $@.dd \
+    -I . -I $(GEN) --name boot --header cpp --depsout $@.dd \
     --set-version $(VERSION) \
     --set-revision $(REVISION)
--include $(GEN)/posix_boot_merged.fs.dd
+-include $(GEN)/posix_boot.h.dd
 
-$(GEN)/posix_boot.h: tools/source_to_string.js $(GEN)/posix_boot_merged.fs | $(GEN)
-	$< boot $(VERSION) $(REVISION) $(GEN)/posix_boot_merged.fs >$@
-
-$(GEN)/windows_boot_extra_merged.fs: windows/windows_boot_extra.fs | $(GEN)
+$(GEN)/windows_boot_extra.h: windows/windows_boot_extra.fs | $(GEN)
 	./tools/importation.py $< $@ \
-    -I . -I $(GEN) --depsout $@.dd \
+    -I . -I $(GEN) --name boot_extra --header win --depsout $@.dd \
     --set-version $(VERSION) \
     --set-revision $(REVISION)
--include $(GEN)/windows_boot_extra_merged.fs.dd
+-include $(GEN)/windows_boot_extra.h.dd
 
-$(GEN)/windows_boot_extra.h: tools/source_to_string.js $(GEN)/windows_boot_extra_merged.fs | $(GEN)
-	$< -win boot_extra $(VERSION) $(REVISION) $(GEN)/windows_boot_extra_merged.fs >$@
-
-$(GEN)/windows_boot_merged.fs: windows/windows_boot.fs | $(GEN)
-	./tools/importation.py $^ $@ \
-    -I . -I $(GEN) --depsout $@.dd \
-    --set-version $(VERSION) \
-    --set-revision $(REVISION)
--include $(GEN)/windows_boot_merged.fs.dd
-
-$(GEN)/windows_boot.h: tools/source_to_string.js $(GEN)/windows_boot_merged.fs | $(GEN)
-	$< -win boot $(VERSION) $(REVISION) $(GEN)/windows_boot_merged.fs >$@
-
-$(GEN)/pico_ice_boot_merged.fs: pico-ice/pico_ice_boot.fs | $(GEN)
-	./tools/importation.py $^ $@ \
-    -I . -I $(GEN) --depsout $@.dd \
-    --set-version $(VERSION) \
-    --set-revision $(REVISION)
--include $(GEN)/pico_ice_boot_merged.fs.dd
-
-$(GEN)/pico_ice_boot.h: tools/source_to_string.js $(GEN)/pico_ice_boot_merged.fs | $(GEN)
-	$< boot $(VERSION) $(REVISION) $(GEN)/pico_ice_boot_merged.fs >$@
-
-$(GEN)/esp32_boot_merged.fs: esp32/esp32_boot.fs | $(GEN)
+$(GEN)/windows_boot.h: windows/windows_boot.fs | $(GEN)
 	./tools/importation.py $< $@ \
-    -I . -I $(GEN) --depsout $@.dd \
+    -I . -I $(GEN) --name boot --header win --depsout $@.dd \
     --set-version $(VERSION) \
     --set-revision $(REVISION)
--include $(GEN)/esp32_boot_merged.fs.dd
+-include $(GEN)/windows_boot.h.dd
 
-$(GEN)/esp32_boot.h: tools/source_to_string.js $(GEN)/esp32_boot_merged.fs | $(GEN)
-	$< boot $(VERSION) $(REVISION) $(GEN)/esp32_boot_merged.fs >$@
+$(GEN)/pico_ice_boot.h: pico-ice/pico_ice_boot.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name boot --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/pico_ice_boot.h.dd
 
-$(GEN)/esp32_assembler.h: \
-    tools/source_to_string.js \
-    common/assembler.fs | $(GEN)
-	$< assembler_source $(VERSION) $(REVISION) \
-    common/assembler.fs >$@
+$(GEN)/esp32_boot.h: esp32/esp32_boot.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name boot --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/esp32_boot.h.dd
 
-$(GEN)/esp32_xtensa-assembler.h: \
-    tools/source_to_string.js \
-    esp32/optional/assemblers/xtensa-assembler.fs | $(GEN)
-	$< xtensa_assembler_source $(VERSION) $(REVISION) \
-    esp32/optional/assemblers/xtensa-assembler.fs >$@
+$(GEN)/esp32_assembler.h: common/assembler.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name assembler_source --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/esp32_assembler.h.dd
 
-$(GEN)/esp32_riscv-assembler.h: \
-    tools/source_to_string.js \
-    esp32/optional/assemblers/riscv-assembler.fs | $(GEN)
-	$< riscv_assembler_source $(VERSION) $(REVISION) \
-    esp32/optional/assemblers/riscv-assembler.fs >$@
+$(GEN)/esp32_xtensa-assembler.h: esp32/optional/assemblers/xtensa-assembler.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name xtensa_assembler_source --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/esp32_xtensa-assembler.h.dd
 
-$(GEN)/esp32_camera.h: \
-    tools/source_to_string.js \
-    esp32/optional/camera/camera_server.fs \
-    esp32/optional/camera/camera.fs | $(GEN)
-	$< camera_source $(VERSION) $(REVISION) \
-    esp32/optional/camera/camera.fs \
-    esp32/optional/camera/camera_server.fs >$@
+$(GEN)/esp32_riscv-assembler.h: esp32/optional/assemblers/riscv-assembler.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name riscv_assembler_source --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/esp32_riscv-assembler.h.dd
 
-$(GEN)/esp32_interrupts.h: \
-    tools/source_to_string.js \
-    esp32/optional/interrupts/interrupts.fs \
-    esp32/optional/interrupts/timers.fs | $(GEN)
-	$< interrupts_source $(VERSION) $(REVISION) \
-    esp32/optional/interrupts/interrupts.fs \
-    esp32/optional/interrupts/timers.fs >$@
+$(GEN)/esp32_camera.h: esp32/optional/camera/camera_server.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name camera_source --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/esp32_camera.h.dd
 
-$(GEN)/esp32_oled.h: \
-    tools/source_to_string.js esp32/optional/oled/oled.fs | $(GEN)
-	$< oled_source $(VERSION) $(REVISION) \
-    esp32/optional/oled/oled.fs >$@
+$(GEN)/esp32_interrupts.h: esp32/optional/interrupts/timers.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name interrupts_source --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/esp32_interrupts.h.dd
 
-$(GEN)/esp32_spi-flash.h: \
-    tools/source_to_string.js esp32/optional/spi-flash/spi-flash.fs | $(GEN)
-	$< spi_flash_source $(VERSION) $(REVISION) \
-    esp32/optional/spi-flash/spi-flash.fs >$@
+$(GEN)/esp32_oled.h: esp32/optional/oled/oled.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name oled_source --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/esp32_oled.h.dd
 
-$(GEN)/esp32_serial-bluetooth.h: \
-    tools/source_to_string.js \
-    esp32/optional/serial-bluetooth/bterm.fs \
-    esp32/optional/serial-bluetooth/serial-bluetooth.fs | $(GEN)
-	$< serial_bluetooth_source $(VERSION) $(REVISION) \
-    esp32/optional/serial-bluetooth/serial-bluetooth.fs \
-    esp32/optional/serial-bluetooth/bterm.fs >$@
+$(GEN)/esp32_spi-flash.h: esp32/optional/spi-flash/spi-flash.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name spi_flash_source --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/esp32_spi-flash.h.dd
+
+$(GEN)/esp32_serial-bluetooth.h: esp32/optional/serial-bluetooth/serial-bluetooth.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name serial_blueooth_source --header cpp --depsout $@.dd \
+    --set-version $(VERSION) \
+    --set-revision $(REVISION)
+-include $(GEN)/esp32_serial-bluetooth.h.dd
 
 OPTIONAL_MODULES = \
   $(ESP32)/ESP32forth/assemblers.h \
@@ -371,15 +360,12 @@ $(GEN)/web_dict.js: $(GEN)/dump_web_opcodes | $(GEN)
 $(GEN)/web_sys.js: $(GEN)/dump_web_opcodes | $(GEN)
 	$< sys >$@
 
-$(GEN)/web_boot_merged.fs: web/web_boot.fs | $(GEN)
-	./tools/importation.py $^ $@ \
-    -I . -I $(GEN) --depsout $@.dd \
+$(GEN)/web_boot.js: web/web_boot.fs | $(GEN)
+	./tools/importation.py $< $@ \
+    -I . -I $(GEN) --name boot --header web --depsout $@.dd \
     --set-version $(VERSION) \
     --set-revision $(REVISION)
--include $(GEN)/web_boot_merged.fs.dd
-
-$(GEN)/web_boot.js: tools/source_to_string.js $(GEN)/web_boot_merged.fs | $(GEN)
-	$< -web boot $(VERSION) $(REVISION) $(GEN)/web_boot_merged.fs >$@
+-include $(GEN)/web_boot.js.dd
 
 # ---- RESOURCES ----
 
diff --git a/esp32/optional/camera/camera_server.fs b/esp32/optional/camera/camera_server.fs
index 54f9f4b..6504d61 100644
--- a/esp32/optional/camera/camera_server.fs
+++ b/esp32/optional/camera/camera_server.fs
@@ -12,6 +12,8 @@
 \ See the License for the specific language governing permissions and
 \ limitations under the License.
 
+needs camera.fs
+
 ( Lazy loaded Camera Server )
 : camera-server r~
 
diff --git a/esp32/optional/interrupts/timers.fs b/esp32/optional/interrupts/timers.fs
index d442d48..ec2b9ad 100644
--- a/esp32/optional/interrupts/timers.fs
+++ b/esp32/optional/interrupts/timers.fs
@@ -12,6 +12,8 @@
 \ See the License for the specific language governing permissions and
 \ limitations under the License.
 
+needs interrupts.fs
+
 internals definitions
 transfer timers-builtins
 forth definitions
diff --git a/esp32/optional/serial-bluetooth/serial-bluetooth.fs b/esp32/optional/serial-bluetooth/serial-bluetooth.fs
index c032367..1a684bd 100644
--- a/esp32/optional/serial-bluetooth/serial-bluetooth.fs
+++ b/esp32/optional/serial-bluetooth/serial-bluetooth.fs
@@ -12,6 +12,8 @@
 \ See the License for the specific language governing permissions and
 \ limitations under the License.
 
+needs bterm.fs
+
 DEFINED? SerialBT.new [IF]
   vocabulary bluetooth   bluetooth definitions
   transfer bluetooth-builtins
diff --git a/tools/configure.py b/tools/configure.py
index 9572125..d7e63ef 100755
--- a/tools/configure.py
+++ b/tools/configure.py
@@ -94,14 +94,10 @@ rule mkdir
   description = mkdir
   command = mkdir -p $out
 
-rule source_to_string
-  description = source_to_string
-  command = ../tools/source_to_string.js $name $version $revision $in >$out
-
 rule importation
-  description = import
+  description = importation
   depfile = $out.dd
-  command = ../tools/importation.py $in $out -I . -I .. --depsout $out.dd --set-version $version --set-revision $revision
+  command = ../tools/importation.py $in $out -I . -I .. --name $name --header $header_mode --depsout $out.dd --set-version $version --set-revision $revision
 
 build gen: mkdir
 
@@ -113,23 +109,20 @@ build gen: mkdir
   'libs': ' '.join(LIBS),
 }
 
-def ForthHeader(target, name, source):
+def ForthHeader(target, name, source, header_mode='cpp'):
+  source = '../' + source
   global output
-  output += """
-build %(target)s: source_to_string %(target)s.merged | gen
-  name = %(name)s
-
-build %(target)s.merged: importation %(source)s | gen
-""" % {
-    'target': target,
-    'source': os.path.join('..', source),
-    'name': name,
-  }
+  output += f"""
+build {target}: importation {source} | gen
+  name = {name}
+  header_mode = {header_mode}
+"""
 
 ForthHeader('gen/posix_boot.h', 'boot', 'posix/posix_boot.fs')
-ForthHeader('gen/window_boot.h', 'boot', 'windows/windows_boot.fs')
-ForthHeader('gen/window_boot_extra.h', 'boot_extra', 'windows/windows_boot_extra.fs')
+ForthHeader('gen/window_boot.h', 'boot', 'windows/windows_boot.fs', header_mode='win')
+ForthHeader('gen/window_boot_extra.h', 'boot_extra', 'windows/windows_boot_extra.fs', header_mode='win')
 ForthHeader('gen/pico_ice_boot.h', 'boot', 'pico-ice/pico_ice_boot.fs')
 ForthHeader('gen/esp32_boot.h', 'boot', 'esp32/esp32_boot.fs')
+ForthHeader('gen/web_boot.js', 'boot', 'esp32/esp32_boot.fs', header_mode='web')
 
 print(output)
diff --git a/tools/importation.py b/tools/importation.py
index 03ad8de..0f9a2e5 100755
--- a/tools/importation.py
+++ b/tools/importation.py
@@ -15,6 +15,8 @@ parser.add_argument('--set-revision')
 parser.add_argument('--depsout')
 parser.add_argument('--no-out', action='store_true')
 parser.add_argument('--keep-first-comment', action='store_true')
+parser.add_argument('--name')
+parser.add_argument('--header')
 args = parser.parse_args()
 bases = args.I or []
 
@@ -88,6 +90,25 @@ def Process():
   # Emit expanded file.
   if not args.no_out:
     with open(args.output, 'w') as fh:
-      fh.write('\n'.join(output) + '\n')
+      if args.header == 'web':
+        fh.write('const ' + args.name + ' = `\n' +
+                 '\n'.join(output) + '\n`;\n')
+      elif args.header == 'cpp':
+        fh.write('const char ' + args.name + '[] = R"""(\n' +
+                 '\n'.join(output) + '\n)""";\n')
+      elif args.header == 'win':
+        fixed = []
+        for line in output:
+          line = line.replace('\\', '\\\\')
+          line = line.replace('"', '\\"')
+          line = '"' + line + '\\n"'
+          if line.startswith('"(') and line.endswith(')\\n"'):
+            line = '// ' + line
+          if line:
+            fixed.append(line)
+        fh.write('const char ' + args.name + '[] =\n' +
+                 '\n'.join(fixed) + '\n;\n')
+      else:
+        fh.write('\n'.join(output) + '\n')
 
 Process()
diff --git a/tools/source_to_string.js b/tools/source_to_string.js
deleted file mode 100755
index e10415e..0000000
--- a/tools/source_to_string.js
+++ /dev/null
@@ -1,69 +0,0 @@
-#! /usr/bin/env nodejs
-// Copyright 2021 Bradley D. Nelson
-//
-// 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.
-
-var fs = require('fs');
-
-function DropCopyright(source) {
-  var lines = source.split('\n');
-  var cleaned = [];
-  for (var i = 0; i < lines.length; ++i) {
-    if (lines[i].search('Copyright') >= 0) {
-      while (lines[i] != '') {
-        ++i;
-      }
-    } else {
-      cleaned.push(lines[i]);
-    }
-  }
-  return cleaned.join('\n');
-}
-
-var is_windows = false;
-var is_web = false;
-
-var args = process.argv.slice(2);
-if (args.length > 0 && args[0] == '-win') {
-  is_windows = true;
-  args.shift();
-}
-if (args.length > 0 && args[0] == '-web') {
-  is_web = true;
-  args.shift();
-}
-var name = args.shift();
-var version = args.shift();
-var revision = args.shift();
-var source = '';
-while (args.length > 0) {
-  source += DropCopyright(fs.readFileSync(args.shift()).toString());
-}
-
-source = source.replace('{{VERSION}}', version);
-source = source.replace('{{REVISION}}', revision);
-
-if (is_windows) {
-  source = source.replace(/\\/g, '\\\\');
-  source = source.replace(/["]/g, '\\"');
-  source = '"' + source.split('\n').join('\\n"\n"') + '\\n"';
-  source = source.replace(/["]  ["]/g, '');
-  source = source.replace(/["] [(] ([^)]*)[)] ["]/g, '// $1');
-  source = 'const char ' + name + '[] =\n' + source + ';\n';
-} else if (is_web) {
-  source = 'const ' + name + ' = `\n' + source + '`;\n';
-} else {
-  source = 'const char ' + name + '[] = R"""(\n' + source + ')""";\n';
-}
-
-process.stdout.write(source);