Implementation of sort builtin REPL function

- Fixes #465

ast/builtins.go

@@ -65,6 +65,9 @@ var DefaultBuiltins = [...]*Builtin{
 
 	// Graphs
 	WalkBuiltin,
+
+	//Sort
+	Sort,
 }
 
 // BuiltinMap provides a convenient mapping of built-in names to
@@ -653,6 +656,24 @@ var WalkBuiltin = &Builtin{
 	),
 }
 
+/**
+ * Sorting
+ */
+
+// Sort a collection
+// Trying new built-in
+var Sort = &Builtin{
+	Name: "sort",
+	Decl: types.NewFunction(
+		types.Args(
+			types.NewAny(
+				types.NewArray(nil, types.A),
+			),
+		),
+		types.A,
+	),
+}
+
 /**
  * Deprecated built-ins.
  */

ast/term.go

@@ -1294,6 +1294,12 @@ func Item(key, value *Term) [2]*Term {
 	return [2]*Term{key, value}
 }
 
+// SortCollection sorts an array using custom function
+func SortCollection(a []*Term) int {
+	sort.Sort(termSlice(a))
+	return 0
+}
+
 // Compare compares obj to other, return <0, 0, or >0 if it is less than, equal to,
 // or greater than other.
 func (obj *object) Compare(other Value) int {

topdown/aggregates.go

@@ -144,10 +144,29 @@ func builtinMin(a ast.Value) (ast.Value, error) {
 	return nil, builtins.NewOperandTypeErr(1, a, ast.SetTypeName, ast.ArrayTypeName)
 }
 
+func builtinSort(a ast.Value) (ast.Value, error) {
+	switch a := a.(type) {
+	case ast.Array:
+		if len(a) == 0 {
+			return nil, BuiltinEmpty{}
+		}
+		ast.SortCollection(a)
+		return a, nil
+	case ast.Set:
+		if a.Len() == 0 {
+			return nil, BuiltinEmpty{}
+		}
+		return a, nil
+	}
+
+	return nil, builtins.NewOperandTypeErr(1, a, ast.SetTypeName, ast.ArrayTypeName)
+}
+
 func init() {
 	RegisterFunctionalBuiltin1(ast.Count.Name, builtinCount)
 	RegisterFunctionalBuiltin1(ast.Sum.Name, builtinSum)
 	RegisterFunctionalBuiltin1(ast.Product.Name, builtinProduct)
 	RegisterFunctionalBuiltin1(ast.Max.Name, builtinMax)
 	RegisterFunctionalBuiltin1(ast.Min.Name, builtinMin)
+	RegisterFunctionalBuiltin1(ast.Sort.Name, builtinSort)
 }

topdown/topdown_test.go

@@ -961,6 +961,7 @@ func TestTopDownAggregates(t *testing.T) {
 		{"min virtual set", []string{`p = x { min(q, x) }`, `q[x] { a[_] = x }`}, "1"},
 		{"reduce ref dest", []string{`p = true { max([1, 2, 3, 4], a[3]) }`}, "true"},
 		{"reduce ref dest (2)", []string{`p = true { not max([1, 2, 3, 4, 5], a[3]) }`}, "true"},
+		{"sort", []string{`p = x { sort([4, 3, 2, 1], x) }`}, "[1 ,2, 3, 4]"},
 	}
 
 	data := loadSmallTestData()