cong-common: correct the doc for default ctors

Author: james-d-mitchell

src/cong-common.cpp

@@ -72,9 +72,11 @@ namespace libsemigroups {
 
       fmt::format_to(std::back_inserter(result),
                      fmt_string,
-                     "detail"_a  = extra_doc.detail,
-                     "example"_a = extra_doc.example,
-                     "name"_a    = name,
+                     "detail"_a           = extra_doc.detail,
+                     "example"_a          = extra_doc.example,
+                     "extra_kwargs"_a     = extra_doc.extra_kwargs,
+                     "extra_kwargs_doc"_a = extra_doc.extra_kwargs_doc,
+                     "name"_a             = name,
                      "only_document_once"_a
                      = extra_doc.only_document_once ? only_doc_once : "",
                      "raises"_a = extra_doc.raises,
@@ -92,11 +94,15 @@ namespace libsemigroups {
                              doc                           extra_doc) {
     thing.def(py::init<>(),
               make_doc(R"pbdoc(
-:sig=() -> None:
+:sig=(word: type{extra_kwargs}) -> None:
 {only_document_once}
 
-Default constructor. This function default constructs an
-uninitialised :any:`{name}` instance.
+Default constructor.
+
+This function default constructs an uninitialised :any:`{name}` instance.
+
+:Keyword Arguments:
+    * **word** (*type*) -- the type of words to use, must be either ``str`` or ``list[int]``{extra_kwargs_doc}
 
 {detail}
 )pbdoc",

src/cong-common.hpp

@@ -33,10 +33,12 @@ namespace libsemigroups {
   // declared below.
   struct doc {
     std::string_view detail             = "";
+    std::string_view example            = "";
+    std::string_view extra_kwargs       = "";
+    std::string_view extra_kwargs_doc   = "";
     bool             only_document_once = false;
     std::string_view raises             = "";
     std::string_view var                = "";
-    std::string_view example            = "";
   };
 
   ////////////////////////////////////////////////////////////////////////

src/knuth-bendix.cpp

@@ -78,7 +78,12 @@ nested class :any:`KnuthBendix.options`.
 
       ////////////////////////////////////////////////////////////////////////
 
-      def_construct_default(thing, "KnuthBendix");
+      def_construct_default(
+          thing,
+          "KnuthBendix",
+          doc{.extra_kwargs = ", rewriter: str", .extra_kwargs_doc = R"pbdoc(
+    * **rewriter** (*str*) -- the type of rewriter to use, must be either ``"RewriteTrie"`` or ``"RewriteFromLeft"``.)pbdoc"sv});
+
       def_init_default(thing, "KnuthBendix");
       def_construct_kind_presentation(thing, "KnuthBendix");
       def_init_kind_presentation(thing, "KnuthBendix");
@@ -117,9 +122,9 @@ the current rules in the :py:class:`KnuthBendix` instance.
       // Helper functions - specific to KnuthBendix
       ////////////////////////////////////////////////////////////////////////
 
-      // This does not use def_normal_forms in cong-common.hpp because it does
-      // not return an Iterator object, and hence has its own implementation
-      // and doc.
+      // This does not use def_normal_forms in cong-common.hpp because it
+      // does not return an Iterator object, and hence has its own
+      // implementation and doc.
       m.def(
           "knuth_bendix_normal_forms",
           [](KnuthBendix_& ci) { return congruence_common::normal_forms(ci); },
@@ -336,7 +341,7 @@ Copy a :any:`NormalFormRange` object.
                 });
       thing.def("next", [](NormalFormRange& nfr) { nfr.next(); });
     }  // bind_normal_form_range
-  }    // namespace
+  }  // namespace
 
   template <typename Word>
   void bind_redundant_rule(py::module& m) {