From 660f0ccb6b7e6fff8a6d870b720b5bd0dd6898a4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Mon, 20 Dec 2021 23:05:05 +0100
Subject: find-extreme on empty list now an error.

---
 module/calp/util.scm |  3 +--
 tests/util.scm       | 22 +++++++++++++++++++++-
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/module/calp/util.scm b/module/calp/util.scm
index 96ca2f01..6cee1b0f 100644
--- a/module/calp/util.scm
+++ b/module/calp/util.scm
@@ -252,8 +252,7 @@
 ;; Ord b => (list a) [, (b, b -> bool), (a -> b)] -> a, (list a)
 (define*-public (find-extreme items optional: (< <) (access identity))
   (if (null? items)
-      ;; Vad fan retunerar man här?
-      (values #f '())
+      (error "Can't find extreme in an empty list")
       (fold-values
        (lambda (c min other)
          (if (< (access c) (access min))
diff --git a/tests/util.scm b/tests/util.scm
index 57d2e538..de8d4b2a 100644
--- a/tests/util.scm
+++ b/tests/util.scm
@@ -2,7 +2,8 @@
 ;; Checks some prodecuders from (calp util)
 ;;; Code:
 
-(((calp util) filter-sorted set/r!))
+(((calp util) filter-sorted set/r!
+  find-min find-max))
 
 (test-equal "Filter sorted"
   '(3 4 5)
@@ -16,3 +17,22 @@
 (test-error
  'syntax-error
  (test-read-eval-string "(set/r! x err not)"))
+
+
+(call-with-values (lambda () (find-min (iota 10)))
+  (lambda (extreme rest)
+    (test-equal "Found correct minimum"
+      0 extreme)
+    (test-equal "Removed \"something\" from the set"
+      9 (length rest))))
+
+
+(call-with-values (lambda () (find-max '("Hello" "Test" "Something long") string-length))
+  (lambda (extreme rest)
+    (test-equal "Found the longest string" "Something long" extreme)
+    (test-equal "Removed the string" 2 (length rest))
+    (test-assert "Other members left 1" (member "Hello" rest))
+    (test-assert "Other members left 2" (member "Test" rest))))
+
+
+(test-error 'misc-error (find-extreme '()))
-- 
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