make library hierarchy

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diff --git a/SAHP/SAHP.internal-portable.scm b/SAHP/SAHP.internal-portable.scm
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+#| Copyright 2024 Peter McGoron
+ |
+ | 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.
+ |#
+
+#| A portable implementation of `extract-SAHP-descriptor`, `make-new-SAHP`
+   using a unexported sentinel object.
+|#
+
+(define SAHP-sentinel-value
+  (vector #f))
+
+(define (extract-SAHP-descriptor SAHP)
+  (SAHP SAHP-sentinel-value))
+
+(define (make-new-SAHP)
+  (let ((SAHP (make-SAHP-descriptor (make-symbol-mapping)
+                                    (make-parameter (make-symbol-mapping))
+                                    (make-symbol-hash-table)))))
+  (lambda (arg1 . arg-rest)
+    (if (eq? arg1 SAHP-sentinel-value)
+        SAHP
+        (call-SAHP SAHP (type-of arg1) (cons arg1 arg-rest)))))