Well, I really made a mess with the last commit; this one sorts it out.

src/c/ops/reverse.c

@@ -0,0 +1,55 @@
+/**
+ *  ops/reverse.c
+ *
+ *  Post Scarcity Software Environment: reverse.
+ *
+ *  Reverse a sequence. Didn'e want to do this in the substrate, but I need
+ *  if for reading atoms!.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#include <stdbool.h>
+
+#include "memory/node.h"
+#include "memory/pointer.h"
+#include "memory/pso.h"
+#include "memory/pso2.h"
+#include "memory/tags.h"
+
+#include "payloads/cons.h"
+#include "payloads/exception.h"
+#include "payloads/psse_string.h"
+
+#include "ops/string_ops.h"
+#include "ops/truth.h"
+
+struct pso_pointer reverse( struct pso_pointer sequence) {
+	struct pso_pointer result = nil;
+
+	for (struct pso_pointer cursor = sequence; !nilp( sequence); cursor = cdr(cursor)) {
+		struct pso2* object = pointer_to_object( cursor);
+		switch (get_tag_value(cursor)) {
+		case CONSTV :
+				result = cons( car(cursor), result);
+				break;
+		case KEYTV :
+			result = make_string_like_thing( object->payload.string.character, result, KEYTAG);
+			break;
+		case STRINGTV :
+			result = make_string_like_thing( object->payload.string.character, result, STRINGTAG);
+			break;
+		case SYMBOLTV :
+			result = make_string_like_thing( object->payload.string.character, result, SYMBOLTAG);
+			break;
+		default :
+			result = make_exception( c_string_to_lisp_string(L"Invalid object in sequence"), nil, nil);
+			goto exit;
+			break;
+		}
+	}
+exit:
+
+	return result;
+}