From 9dd7d9c74b04a1f25ac2adf75cc464a2a9149b50 Mon Sep 17 00:00:00 2001
From: Arun Isaac
Date: Wed, 8 Apr 2026 20:33:21 +0100
Subject: Add foldn.

---
 kaakaa/utils.scm | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/kaakaa/utils.scm b/kaakaa/utils.scm
index 5677af2..a922ef2 100644
--- a/kaakaa/utils.scm
+++ b/kaakaa/utils.scm
@@ -22,6 +22,7 @@
   #:use-module (ice-9 match)
   #:use-module (ice-9 popen)
   #:export (->
+            foldn
             alist->plist
             call-with-input-pipe))
 
@@ -43,6 +44,27 @@ For example:
 => 16"
   (->-helper x (cut proc ...) ...))
 
+(define (foldn proc lst . inits)
+  "Apply @var{proc} to the elements of @var{lst} to build a result, and return
+that result. @var{proc} may return multiple values, in which case, an equal
+number of values are returned. Each @var{proc} call is @code{(proc element
+previous ...)} where @code{element} is an element of @var{lst}, and
+@code{(previous ...)} is the return from the previous call to @var{proc} or the
+given @var{inits} for the first call. For example,
+
+(foldn (lambda (n sum sum-of-squares)
+         (values (+ sum n)
+                 (+ sum-of-squares (expt n 2))))
+       (iota 10)
+       0 0)
+=> 45
+=> 285"
+  (apply values
+         (fold (lambda (element results)
+                 (call-with-values (cut apply proc element results) list))
+               inits
+               lst)))
+
 (define (alist->plist alist)
   "Convert association list @var{alist} to a property list. Keys in
 @var{alist} are converted to keywords."
-- 
cgit 1.4.1