From c09bcf271262972cc291561c7f42098ae4686129 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Thu, 12 Dec 2024 15:44:52 +0100
Subject: [PATCH] GAP: add and use ReplaceBinding helper

This is a variant of Oscar's `ReplaceGapFunc` but I figure it is
be useful for other code.
---
 gap/exec.g       |  5 +----
 gap/systemfile.g | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/gap/exec.g b/gap/exec.g
index 74080892..77453b1d 100644
--- a/gap/exec.g
+++ b/gap/exec.g
@@ -1,4 +1 @@
-BindGlobal("_ORIG_ExecuteProcess", ExecuteProcess);
-MakeReadWriteGlobal("ExecuteProcess");
-ExecuteProcess := Julia.GAP.GAP_ExecuteProcess;
-MakeReadOnlyGlobal("ExecuteProcess");
+ReplaceBinding("ExecuteProcess", Julia.GAP.GAP_ExecuteProcess);
diff --git a/gap/systemfile.g b/gap/systemfile.g
index d66fe66e..c99221dc 100644
--- a/gap/systemfile.g
+++ b/gap/systemfile.g
@@ -1,3 +1,20 @@
+# Helper for replacing a GAP global variable or function by a new value.
+# The original value is retained under the name `_ORIG_***`
+BIND_GLOBAL("ReplaceBinding", function(name, val)
+  local orig_name;
+  # Store a copy of the original value, but only if that copy does not yet
+  # exist. This ensures we don't overwrite it during a call to `Reread`.
+  orig_name := "_ORIG_";
+  APPEND_LIST_INTR(orig_name, name);
+  if not ISB_GVAR(orig_name) then
+    ASS_GVAR(orig_name, VAL_GVAR(name));
+    MakeReadOnlyGVar(orig_name);
+  fi;
+  MakeReadWriteGVar(name);
+  ASS_GVAR(name, val);
+  MakeReadOnlyGVar(name);
+end);
+
 (function()
     local deps;