types: add Stringer implementation for List

Signed-off-by: Sebastien Binet <[email protected]>

types/list.go

@@ -4,7 +4,10 @@
 
 package types
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 // ListAppender is implemented by any value that exhibits a list-like
 // behaviour, allowing arbitrary values to be appended.
@@ -59,3 +62,19 @@ func (*List) Call(args ...interface{}) (interface{}, error) {
 	}
 	return nil, fmt.Errorf("List: invalid arguments: %#v", args)
 }
+
+func (l *List) String() string {
+	if l == nil {
+		return "nil"
+	}
+	o := new(strings.Builder)
+	o.WriteString("[")
+	for i, v := range *l {
+		if i > 0 {
+			o.WriteString(", ")
+		}
+		fmt.Fprintf(o, "%v", v)
+	}
+	o.WriteString("]")
+	return o.String()
+}

types/list_test.go

@@ -1,6 +1,12 @@
+// Copyright 2023 NLP Odyssey Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 package types
 
 import (
+	"bytes"
+	"fmt"
 	"testing"
 )
 
@@ -15,3 +21,20 @@ func TestCall(t *testing.T) {
 		t.Errorf("expected %v, actual: %v", expected, actual)
 	}
 }
+
+func TestListStringer(t *testing.T) {
+	pylist := func(sli ...interface{}) *List {
+		return NewListFromSlice(sli)
+	}
+
+	lst := pylist(pylist(), pylist(1), pylist(2, 3), pylist(pylist(4, 5), 6))
+
+	buf := new(bytes.Buffer)
+	fmt.Fprintf(buf, "%v", lst)
+	got := buf.String()
+	want := "[[], [1], [2, 3], [[4, 5], 6]]"
+
+	if got != want {
+		t.Fatalf("got= %q\nwant=%q", got, want)
+	}
+}