From 7b161c64b1c8d5a77942a10757f835f36a67e5cf Mon Sep 17 00:00:00 2001
From: Chris Novakovic <chris@chrisn.me.uk>
Date: Wed, 11 Jun 2025 11:33:31 +0100
Subject: [PATCH] Implement `reverse` parameter for `sorted` built-in function

This is optional, and behaves similarly to the `reverse` parameter in
Python's `sorted` built-in function: if the value is `True`, the list is
sorted in reverse order. This is a more efficient equivalent to
`reversed(sorted(...))`.
---
 docs/lexicon.html                                |  6 ++++--
 rules/builtins.build_defs                        |  2 +-
 src/parse/asp/builtins.go                        | 10 ++++++++--
 src/parse/asp/interpreter_test.go                |  2 ++
 src/parse/asp/test_data/interpreter/sorted.build |  4 ++++
 5 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/docs/lexicon.html b/docs/lexicon.html
index 3090834c8b..49ee4c2660 100644
--- a/docs/lexicon.html
+++ b/docs/lexicon.html
@@ -159,11 +159,13 @@ <h2 class="title-2" id="python-builtins">
         <code class="code"
           ><span class="fn-name">sorted</span><span class="fn-p">(</span
           ><span class="fn-arg">seq</span>[,<span class="fn-arg">key</span
-          >]<span class="fn-p">)</span></code
+          >][,<span class="fn-arg">reverse</span>]<span class="fn-p"
+          >)</span></code
         >
         - returns a copy of <code class="code">seq</code> with the contents
         sorted. <code class="code">key</code> is a function that is applied
-        to each item before comparison.
+        to each item before comparison. If <code class="code">reverse</code
+        > is true, the items are sorted in reverse order.
       </span>
     </li>
     <li>
diff --git a/rules/builtins.build_defs b/rules/builtins.build_defs
index 5488f9f105..a8c9fcfd2e 100644
--- a/rules/builtins.build_defs
+++ b/rules/builtins.build_defs
@@ -125,7 +125,7 @@ def glob(include:list|str, exclude:list|str&excludes=[], hidden:bool=CONFIG.BAZE
 def package():
     pass
 
-def sorted(seq:list, key:function=None) -> list:
+def sorted(seq:list, key:function=None, reverse:bool=False) -> list:
     pass
 
 def reversed(seq:list) -> list:
diff --git a/src/parse/asp/builtins.go b/src/parse/asp/builtins.go
index 8ce3e24680..69c2564c17 100644
--- a/src/parse/asp/builtins.go
+++ b/src/parse/asp/builtins.go
@@ -800,11 +800,17 @@ func dictCopy(s *scope, args []pyObject) pyObject {
 func sorted(s *scope, args []pyObject) pyObject {
 	l, isList := args[0].(pyList)
 	key, isFunc := args[1].(*pyFunc)
+	reverse, isBool := args[2].(pyBool)
 	s.Assert(isList, "Argument seq must be a list, not %s", args[0].Type())
+	s.Assert(isBool, "Argument reverse must be a bool, not %s", args[2].Type())
+	order := LessThan
+	if reverse {
+		order = GreaterThan
+	}
 	l = l[:]
 	if key == nil {
 		sort.Slice(l, func(i, j int) bool {
-			return s.operator(LessThan, l[i], l[j]).IsTruthy()
+			return s.operator(order, l[i], l[j]).IsTruthy()
 		})
 	} else {
 		s.Assert(isFunc, "Argument key must be callable, not %s", args[1].Type())
@@ -819,7 +825,7 @@ func sorted(s *scope, args []pyObject) pyObject {
 					Value: Expression{optimised: &optimisedExpression{Constant: l[j]}},
 				}},
 			})
-			return s.operator(LessThan, iKey, jKey).IsTruthy()
+			return s.operator(order, iKey, jKey).IsTruthy()
 		})
 	}
 	return l
diff --git a/src/parse/asp/interpreter_test.go b/src/parse/asp/interpreter_test.go
index 6a8faa3c11..d94fce0f6c 100644
--- a/src/parse/asp/interpreter_test.go
+++ b/src/parse/asp/interpreter_test.go
@@ -172,6 +172,8 @@ func TestInterpreterSorting(t *testing.T) {
 	// N.B. sorted() sorts in-place, unlike Python's one. We may change that later.
 	assert.Equal(t, pyList{pyInt(1), pyInt(2), pyInt(3)}, s.Lookup("r1"))
 	assert.Equal(t, pyList{pyString("ONE"), pyString("THREE"), pyString("two")}, s.Lookup("r2"))
+	assert.Equal(t, pyList{pyInt(4), pyInt(3), pyInt(2), pyInt(1)}, s.Lookup("r3"))
+	assert.Equal(t, pyList{pyInt(1), pyInt(2), pyInt(3), pyInt(4)}, s.Lookup("r4"))
 }
 
 func TestReversed(t *testing.T) {
diff --git a/src/parse/asp/test_data/interpreter/sorted.build b/src/parse/asp/test_data/interpreter/sorted.build
index 29e2d58f33..4125a388cb 100644
--- a/src/parse/asp/test_data/interpreter/sorted.build
+++ b/src/parse/asp/test_data/interpreter/sorted.build
@@ -4,3 +4,7 @@ r1 = sorted(l1)
 # key parameter test
 l2 = ["ONE", "two", "THREE"]
 r2 = sorted(l2, key=lambda s: s.lower())
+
+# reverse parameter test
+r3 = sorted([2, 4, 1, 3], reverse=True)
+r4 = sorted([2, 4, 1, 3], reverse=False)