#| 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)))))