cond-thunk

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diff --git a/README.md b/README.md
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+# COND-THUNK
+
+License: Apache-2.0
+
+`cond-thunk` is a library that abstracts conditionals into procedures
+called *conditional procedues* (ct). This allows the programmer to
+abstract conditional branches into procedures or macros, allowing for
+multiple value binding or backtracking.
+
+Documentation for this library is in the format of index.scheme.org and
+is located in `doc`.
diff --git a/doc/mcgoron.cond-thunk.scm b/doc/mcgoron.cond-thunk.scm
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+++ b/doc/mcgoron.cond-thunk.scm
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+(((name . "cond-thunk")
+  (signature syntax-rules (else)
+             ((_ clause ...)))
+  (subsigs (clause
+            (pattern
+             (expr clause ...)
+             (else expression1 expression2 ...)))
+           (expr (or (lambda () *) #f)))
+  (desc "
+* It is an error if `expr` does not evaluate to a thunk or to `#f`.
+
+If `expr` evaluates to a thunk, then the thunk is tail-called as the
+result of the expression. Otherwise the macro evalates the next clause. If
+the `else` clause is reached, the expressions in the clause are evaluated
+as the result of the expression. If there is no `else` clause and all
+`expr` fail, then `cond-thunk` returns #f."))
+ ((name . "any-thunk")
+  (signature case-lambda
+             ((list? thunks) *)
+             ((list? thunks) (procedure? else-thunk) *))
+  (desc "
+* It is an error if `thunks` is not a proper list of thunks that return
+  either `#f` or another thunk.
+* It is an error if `else-thunk` isnot a thunk.
+
+This function is a procedural version of `cond-thunk`.
+
+Evaluate each `thunk` in `thunks` in order. If the `thunk` evaluates to
+a thunk, the thunk is tail-called. Otherwise evaluate the next thunk in
+the list.
+
+If all `thunks` evaluate to `#f`, then `else-thunk` is tail called. If
+`else-thunk` is not supplied, the function returns `#f`."))
+ ((name . "when-ct")
+  (signature syntax-rules ((_ conditional body ...)))
+  (desc "
+* It is an error if `formal` is not a lambda formal.
+* It is an error if `conditional` is not an expression.
+
+If `conditional` is true, return a thunk that when called executes
+`body ...`. Otherwise return `#f`."))
+ ((name . "lambda-ct")
+  (signature syntax-rules ((_ formal conditional body ...)))
+  (desc "
+* It is an error if `formal` is not a lambda formal.
+* It is an error if `conditional` is not an expression.
+
+Create a closure with arguments `formal` that evaluates `conditional`.
+If `conditional` returns a truthy value, a thunk closure with
+`body ...` as its body is returned. Otherwise the closure returns `#f`."))
+ (name . "define-ct")
+ (signature syntax-rules ((_ (name . formal) conditional body ...)))
+ (desc "
+* It is an error if `formal` is not a lambda formal.
+* It is an error if `conditional` is not an expression.
+
+Define a procedure `name` as a conditional generating a thunk. See
+`lambda-ct` for more details."))
\ No newline at end of file
diff --git a/mcgoron.cond-thunk.scm b/mcgoron.cond-thunk.scm
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+++ 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 ...)))))
+
diff --git a/mcgoron.cond-thunk.sld b/mcgoron.cond-thunk.sld
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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-library (mcgoron cond-thunk)
+  (import (scheme base) (scheme case-lambda))
+  (export cond-thunk any-thunk
+          when-ct
+          lambda-ct define-ct)
+  (include "mcgoron.cond-thunk.scm"))
diff --git a/mcgoron.cond-thunk.test.scm b/mcgoron.cond-thunk.test.scm
new file mode 100644
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--- /dev/null
+++ b/mcgoron.cond-thunk.test.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.
+ |#
+
+(cond-expand
+ (chicken (import test r7rs))
+ (else (import (srfi 64))))
+
+(load "mcgoron.cond-thunk.sld")
+(import (mcgoron cond-thunk))
+
+(test-assert
+ "cond-thunk basic"
+ (cond-thunk
+   (if #t
+       (lambda ()
+         #t)
+       #f)
+   (else #f)))
+
+(test-assert
+ "when-ct true"
+ (cond-thunk
+   (when-ct #t #t)
+   (else #f)))
+
+(test
+ "cond-thunk multiple branches"
+ 'two
+ (cond-thunk
+   (when-ct (pair? #f) 'one)
+   (when-ct (boolean? #f) 'two)
+   (when-ct (boolean? #f) 'three)
+   (else #f)))
+
+(let ((on-pair
+       (lambda-ct (x) (pair? x)
+         'pair))
+      (on-boolean
+       (lambda-ct (x) (boolean? x)
+         'boolean)))
+  (test
+   "lambda-ct basic"
+   'boolean
+   (cond-thunk
+     (on-pair #f)
+     (on-boolean #f)
+     (else #f))))
+
+(let ()
+  (define-ct (on-pair x) (pair? x)
+    'pair)
+  (define-ct (on-boolean x) (boolean? x)
+    'boolean)
+  (test
+   "define-ct basic"
+   'boolean
+   (cond-thunk
+     (on-pair #f)
+     (on-boolean #f)
+     (else #f))))
+