factor into libraries

1 files changed, 38 insertions, 0 deletions

diff --git a/values-lib.scm b/values-lib.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.
+
+;;; Helper function.
+(define (null-cdr? lst) (null? (cdr lst)))
+
+;;; MAP-VALUES returns (VALUES L1 L2 ...), where L1 is the first
+;;; value returned from (F (CAR LST)), (F (CADR LST)), ... and so on.
+(define (map-values f . lists)
+  (define (null-cdr? lst) (null? (cdr lst)))
+  (let-values ((new-values (apply f (map car lists))))
+    (if (any null-cdr? lists)
+        (apply values (map list new-values))
+        (let-values ((returned (apply map-values f (map cdr lists))))
+          (apply values (map cons new-values returned))))))
+
+;;; (ANY-VALUES F (A1 A2 ...) (B1 B2 ...) ...) runs
+;;; (F A1 B1 ...) and checks if there any returned values. If there are
+;;; none, runs (F A2 B2 ...), and so on.
+;;; 
+;;; If any of the lists end, then ANY-VALUES returns no values.
+(define (any-values f . lists)
+  (after ((when (not (null? lists)))
+          (when (all pair? lists)))
+    (let-values ((returned (apply f (map car lists))))
+      (if (null? returned)
+          (apply any-values f (map cdr lists))
+          (apply values returned)))))