cond-thunk

1 files changed, 59 insertions, 0 deletions

diff --git a/mcgoron.cond-thunk.scm b/mcgoron.cond-thunk.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.
+ |#
+
+(define-syntax cond-thunk
+  (syntax-rules (else)
+    ((cond-thunk (else body ...))
+     (begin body ...))
+    ((cond-thunk expr rest ...)
+     (let ((value expr))
+       (if value
+           (value)
+           (cond-thunk rest ...))))
+    ((cond-thunk) #f)))
+
+(define any-thunk
+  (letrec ((loop
+            (lambda (thunks else-thunk)
+              (if (null? thunks)
+                  (else-thunk)
+                  (let* ((thunk (car thunks))
+                         (result (thunk)))
+                    (if (not result)
+                        (loop (cdr thunks))
+                        (result)))))))
+    (case-lambda
+      ((thunks) (loop thunks (lambda () #f)))
+      ((thunks else-thunk) (loop thunks else-thunk)))))
+
+(define-syntax when-ct
+  (syntax-rules ()
+    ((when-ct conditional body ...)
+     (if conditional
+         (lambda () body ...)
+         #f))))
+
+(define-syntax lambda-ct
+  (syntax-rules ()
+    ((lambda-ct formal conditional body ...)
+     (lambda formal (when-ct conditional body ...)))))
+
+(define-syntax define-ct
+  (syntax-rules ()
+    ((define-ct (name . formal) conditional body ...)
+     (define name
+       (lambda-ct formal conditional body ...)))))
+