From 48df59c37e5fb1a2f5061589bfba4e3c155e2f08 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Fri, 5 Mar 2021 07:47:57 -0500
Subject: utils: Add for-range macro.

---
 .dir-locals.el      |  3 ++-
 chickadee/utils.scm | 24 +++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/.dir-locals.el b/.dir-locals.el
index f255f96..9eb5b8e 100644
--- a/.dir-locals.el
+++ b/.dir-locals.el
@@ -28,4 +28,5 @@
    (eval . (put 'with-graphics-state! 'scheme-indent-function 1))
    (eval . (put 'translate 'scheme-indent-function 1))
    (eval . (put 'rotate 'scheme-indent-function 1))
-   (eval . (put 'scale 'scheme-indent-function 1)))))
+   (eval . (put 'scale 'scheme-indent-function 1))
+   (eval . (put 'for-range 'scheme-indent-function 1)))))
diff --git a/chickadee/utils.scm b/chickadee/utils.scm
index 4f989ac..e2a20c1 100644
--- a/chickadee/utils.scm
+++ b/chickadee/utils.scm
@@ -17,7 +17,8 @@
 ;;; <http://www.gnu.org/licenses/>.
 
 (define-module (chickadee utils)
-  #:export (memoize))
+  #:export (memoize
+            for-range))
 
 ;; Written by Ludovic Courtès.  Taken from GNU Guix.
 (define (memoize proc)
@@ -31,3 +32,24 @@
                              list)))
               (hash-set! cache args results)
               (apply values results)))))))
+
+(define-syntax for-range
+  (syntax-rules ()
+    ((_ ((var end start inc)) body ...)
+     (let* ((s start) ; evaluate start/end only once
+            (e end)
+            (reverse? (< e s))
+            (start* (if reverse? e s))
+            (end* (if reverse? s e)))
+       (let loop ((var start*))
+         (when (< var end*)
+           body ...
+           (loop (+ var inc))))))
+    ((_ ((var end start)) body ...)
+     (for-range ((var end start 1)) body ...))
+    ((_ ((var end)) body ...)
+     (for-range ((var end 0 1)) body ...))
+    ((_ ((var args ...) rest ...) body ...)
+     (for-range ((var args ...))
+       (for-range (rest ...)
+         body ...)))))
-- 
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