From 58d9d53b2ddc80c5d599f2fde3e265a4beaeccb4 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Mon, 23 Oct 2023 01:00:03 +0200
Subject: [PATCH 1/2] ReplacedString: rename variables to match docs

---
 lib/init.g | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/lib/init.g b/lib/init.g
index 6fec1b1504..cea842f139 100644
--- a/lib/init.g
+++ b/lib/init.g
@@ -102,18 +102,15 @@ infinity := "2b defined";
 ##
 ##  This cannot be inside "kernel.g" because it is needed to read "kernel.g".
 ##
-ReplacedString := function ( arg )
-    local str, substr, lss, subs, all, p, s, pp;
-    str := arg[1];
-    substr := arg[2];
-    lss := LEN_LIST( substr );
-    subs := arg[3];
-    if LEN_LIST( arg ) > 3  then
-        all := arg[4] = "all";
+ReplacedString := function ( str, old, new, arg... )
+    local lss, all, p, s, pp;
+    lss := LEN_LIST( old );
+    if LEN_LIST( arg ) > 0  then
+        all := arg[1] = "all";
     else
         all := true;
     fi;
-    p := POSITION_SUBSTRING( str, substr, 0 );
+    p := POSITION_SUBSTRING( str, old, 0 );
     if p = fail  then
         return str;
     fi;
@@ -121,10 +118,10 @@ ReplacedString := function ( arg )
     pp := 0;
     while p <> fail  do
         APPEND_LIST_INTR( s, str{[ pp+1 .. p - 1 ]} );
-        APPEND_LIST_INTR( s, subs );
+        APPEND_LIST_INTR( s, new );
         pp := p + lss - 1;
         if all  then
-            p := POSITION_SUBSTRING( str, substr, pp );
+            p := POSITION_SUBSTRING( str, old, pp );
         else
             p := fail;
         fi;

From 70bca27c0a54accc637d7e23a8089126b00f2113 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Mon, 23 Oct 2023 01:20:04 +0200
Subject: [PATCH 2/2] Fix infinite recursion in ReplacedString

... when <old> is empty
---
 lib/init.g                  | 6 ++++++
 tst/testinstall/strings.tst | 8 ++++++++
 2 files changed, 14 insertions(+)

diff --git a/lib/init.g b/lib/init.g
index cea842f139..40faba053b 100644
--- a/lib/init.g
+++ b/lib/init.g
@@ -104,7 +104,13 @@ infinity := "2b defined";
 ##
 ReplacedString := function ( str, old, new, arg... )
     local lss, all, p, s, pp;
+    if old = new then
+        return str;
+    fi;
     lss := LEN_LIST( old );
+    if lss = 0  then
+        Error("<old> must not be empty");
+    fi;
     if LEN_LIST( arg ) > 0  then
         all := arg[1] = "all";
     else
diff --git a/tst/testinstall/strings.tst b/tst/testinstall/strings.tst
index d0dd5388b7..84439e4d9a 100644
--- a/tst/testinstall/strings.tst
+++ b/tst/testinstall/strings.tst
@@ -209,5 +209,13 @@ gap> for len in [10,100,1000,10000,100000] do
 > Assert(0, Concatenation(str,"\n") = DisplayString(str));
 > od;;
 
+#
+gap> ReplacedString("Hello world", "Hello", "Goodbye");
+"Goodbye world"
+gap> ReplacedString("Hello world", "", "");
+"Hello world"
+gap> ReplacedString("Hello world", "", "*");
+Error, <old> must not be empty
+
 #
 gap> STOP_TEST( "strings.tst", 1);