From 3c73fd46dd0c487a568911b73346dc29dbbd9a74 Mon Sep 17 00:00:00 2001
From: "Edward L. Platt" <ed@elplatt.com>
Date: Wed, 24 Aug 2022 21:38:03 -0400
Subject: [PATCH] Move utility functions to separate module.

---
 deliberate/utils.scm | 74 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 deliberate/utils.scm

diff --git a/deliberate/utils.scm b/deliberate/utils.scm
new file mode 100644
index 0000000..0171045
--- /dev/null
+++ b/deliberate/utils.scm
@@ -0,0 +1,74 @@
+(define-module (deliberate utils)
+  #:use-module (srfi srfi-1)
+  #:export (const-list range reorder string-count zip))o
+
+(define (const-list length value)
+  (if (= length 0)
+      '()
+      (cons value (const-list (- length 1) value))))
+
+;; Return a list of integers in the half-open interval [low, high)
+(define (range low high)
+  (if (eq? low high)
+      '()
+      (cons low (range (+ 1 low) high))))
+
+;; Combine lists component-wise
+;; Similar to python zip()
+;;
+;; Parameters:
+;;   args: Any number of lists
+;;
+;; Returns:
+;;   A list. The nth element is a list of the
+;;   nth elements of each argument
+;;
+(define (zip . args)
+  (if (or (nil? args) (memq '() args))
+      '()
+      (cons (map car args)
+	    (apply zip (map cdr args)))))
+
+;; Reorder one list by another
+;; A reordering is applied to lst such that the same reordering would
+;; Put rank in asending oder.
+;;
+;; Parameters:
+;;   lst: The list to reorder
+;;   ranks: The list to sort by
+;;
+;; Returns:
+;;   A reordered copy of lst
+;;
+(define (reorder lst ranks)
+  (let* ((pairs (zip lst ranks))
+	 (ranked-pairs
+	  (filter (lambda (pair) (not (eq? #f (cadr pair))))
+		  pairs))
+	 (sorted-pairs
+	   (sort ranked-pairs (lambda (a b) (< (cadr a) (cadr b))))))
+    (map car sorted-pairs)))
+
+
+;; Same as string-count but assumes parameter is sorted
+(define (string-count-sorted sorted)
+  (if (nil? sorted)
+      '()
+      (let* ((elt (car sorted))
+	     (total-length (length sorted))
+	     (rest (find-tail (lambda (x) (not (equal? x elt))) sorted))
+	     (rest-length (if rest (length rest) 0)))
+	(cons (cons elt (- total-length rest-length))
+	      (string-count-sorted rest)))))
+
+;; Counts the number of times each string appears in a list
+;;
+;; Parameters:
+;;   values: The list
+;;
+;; Returns:
+;;   An alist of the form ((string1 . count1) ...)
+;;
+(define (string-count values)
+  (let ((sorted (sort values string<)))
+    (string-count-sorted sorted)))