TIdy small omissions in PR #1251

CHANGES.rst

@@ -35,6 +35,7 @@ Enhancements
 * ``FileNames`` returns a sorted list (#1250).
 * ``FindRoot`` now receives several optional parameters like ``Method`` and ``MaxIterations``.
 * ``FixedPoint`` now supports the ``SameTest`` option.
+* ``Prepend`` works with ``DownValues`` Issue #1251
 * ``Prime`` and ``PrimePi`` now accept a list parameter and have the ``NumericFunction`` attribute.
 * ``Read`` with ``Hold[Expression]`` now supported. (#1242)
 * ``ReplaceRepeated`` and ``FixedPoint`` now supports the ``MaxIteration`` option (#1260).

mathics/builtin/lists.py

@@ -2918,8 +2918,11 @@ def apply(self, s, item, evaluation):
 class Prepend(Builtin):
     """
     <dl>
-    <dt>'Prepend[$expr$, $item$]'
-        <dd>returns $expr$ with $item$ prepended to its leaves.
+     <dt>'Prepend[$expr$, $item$]'
+     <dd>returns $expr$ with $item$ prepended to its leaves.
+
+     <dt>'Prepend[$expr$]'
+     <dd>'Prepend[$elem$][$expr$]' is equivalent to 'Prepend[$expr$,$elem$]'.
     </dl>
 
     'Prepend' is similar to 'Append', but adds $item$ to the beginning

test/test_lists.py

@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*-
+from .helper import check_evaluation
+
+
+def test_calculus():
+    for str_expr, str_expected, message in (
+        (
+            "DownValues[foo]={x_^2:>y}",
+            "{x_ ^ 2 :> y}",
+            "Issue #1251 part 1",
+        ),
+        (
+            "PrependTo[DownValues[foo], {x_^3:>z}]",
+            "{{x_ ^ 3 :> z}, HoldPattern[x_ ^ 2] :> y}",
+            "Issue #1251 part 2",
+        ),
+        (
+            "DownValues[foo]={x_^3:>y}",
+            "{x_ ^ 3 :> y}",
+            "Issue #1251 part 3",
+        ),
+
+    ):
+        check_evaluation(str_expr, str_expected, message)