From 050740aec87f1721a35feea6ababac2a7cc513f4 Mon Sep 17 00:00:00 2001
From: James Mitchell <jdm3@st-andrews.ac.uk>
Date: Wed, 25 Feb 2026 09:40:04 +0000
Subject: [PATCH] Sims: check that Sims1/2 is initialised before add
 SimsRefinerIdeals

---
 src/sims.cpp       | 13 +++++++++++++
 tests/test_sims.py | 11 +++++++++++
 2 files changed, 24 insertions(+)

diff --git a/src/sims.cpp b/src/sims.cpp
index df87d03a..d1c03875 100644
--- a/src/sims.cpp
+++ b/src/sims.cpp
@@ -270,6 +270,19 @@ by :py:meth:`~Sims1.pruners`.
     ss.def(
         "add_pruner",
         [](SimsSettings_& self, SimsRefinerIdeals const& func) -> Subclass& {
+          if (self.presentation().alphabet().empty()
+              && self.presentation().rules.empty()) {
+            throw pybind11::value_error(
+                "the 1st argument (Sims1/2) must be initialised with "
+                "a non-empty presentation before calling this function");
+          }
+          // Can't add this check to libsemigroups itself because it is a
+          // template.
+          if (func.presentation() != self.presentation()) {
+            throw pybind11::value_error(
+                "the 2nd argument (SimsRefinerIdeals) must be initialised with "
+                "the same presentation as the 1st argument (Sims1/2)");
+          }
           return self.add_pruner(func);
         },
         py::arg("pruner"),
diff --git a/tests/test_sims.py b/tests/test_sims.py
index 62172efa..6344ebf9 100644
--- a/tests/test_sims.py
+++ b/tests/test_sims.py
@@ -579,3 +579,14 @@ def test_sims_refiner_ideals_return_policy():
     p.rules = ["a" * 5, "a", "b" * 4, "b", "ab", "ba"]
     q = to(p, rtype=(Presentation, list[int]))
     assert sri.init(q) is sri
+
+
+def test_sims_refiner_ideals_uninit():
+    s = Sims2(word=list[int])
+    sri = SimsRefinerIdeals(word=list[int])
+    with pytest.raises(ValueError):
+        s.add_pruner(sri)
+    p = Presentation([0, 1])
+    s.presentation(p)
+    with pytest.raises(ValueError):
+        s.add_pruner(sri)