From c648a7030f2b2ef172ef7d30bb9009082b685ea8 Mon Sep 17 00:00:00 2001
From: Oliver Steele <steele@osteele.com>
Date: Wed, 28 Jun 2017 09:50:04 -0400
Subject: [PATCH] Implement ar.first, ar.list

---
 expressions/evaluator_test.go |  8 ++++----
 expressions/interpreter.go    | 18 ++++++++++++++----
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/expressions/evaluator_test.go b/expressions/evaluator_test.go
index 04fd3c5..df4b486 100644
--- a/expressions/evaluator_test.go
+++ b/expressions/evaluator_test.go
@@ -29,10 +29,10 @@ var evaluatorTests = []struct {
 	{"ar[100]", nil},
 	{"obj[1]", nil},
 	{"obj.c[0]", "r"},
-	// {`fruits.first`, "apples"},
-	// {`fruits.last`, "plums"},
-	// {`empty_list.first`, ""},
-	// {`empty_list.last`, ""},
+	{`fruits.first`, "apples"},
+	{`fruits.last`, "plums"},
+	{`empty_list.first`, nil},
+	{`empty_list.last`, nil},
 
 	// Operators
 	{"1 == 1", true},
diff --git a/expressions/interpreter.go b/expressions/interpreter.go
index f566431..90a6828 100644
--- a/expressions/interpreter.go
+++ b/expressions/interpreter.go
@@ -8,6 +8,16 @@ func makeObjectPropertyEvaluator(obj func(Context) interface{}, attr string) fun
 	return func(ctx Context) interface{} {
 		ref := reflect.ValueOf(obj(ctx))
 		switch ref.Kind() {
+		case reflect.Array, reflect.Slice:
+			if ref.Len() == 0 {
+				return nil
+			}
+			switch attr {
+			case "first":
+				return ref.Index(0).Interface()
+			case "last":
+				return ref.Index(ref.Len() - 1).Interface()
+			}
 		case reflect.Map:
 			value := ref.MapIndex(reflect.ValueOf(attr))
 			if value.Kind() != reflect.Invalid {
@@ -18,15 +28,15 @@ func makeObjectPropertyEvaluator(obj func(Context) interface{}, attr string) fun
 	}
 }
 
-func makeIndexEvaluator(obj, indexfn func(Context) interface{}) func(Context) interface{} {
+func makeIndexEvaluator(obj, index func(Context) interface{}) func(Context) interface{} {
 	return func(ctx Context) interface{} {
 		ref := reflect.ValueOf(obj(ctx))
-		index := reflect.ValueOf(indexfn(ctx))
+		i := reflect.ValueOf(index(ctx))
 		switch ref.Kind() {
 		case reflect.Array, reflect.Slice:
-			switch index.Kind() {
+			switch i.Kind() {
 			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-				n := int(index.Int())
+				n := int(i.Int())
 				if n < 0 {
 					n = ref.Len() + n
 				}