1 files changed, 88 insertions, 0 deletions
diff --git a/evaluator/builtins.go b/evaluator/builtins.go
index 0e6846a..1c7a312 100644
--- a/evaluator/builtins.go
+++ b/evaluator/builtins.go
@@ -15,9 +15,97 @@ var builtins = map[string]*object.Builtin{
 			switch arg := args[0].(type) {
 			case *object.String:
 				return &object.Integer{Value: int64(len(arg.Value))}
+			case *object.Array:
+				return &object.Integer{Value: int64(len(arg.Elements))}
 			default:
 				return newError("argument to `len` not supported, got %s", arg.Type())
 			}
 		},
 	},
+	"first": {
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1",
+					len(args))
+			}
+
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `first` must be ARRAY, got %s",
+					args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			if len(arr.Elements) > 0 {
+				return arr.Elements[0]
+			}
+
+			return NULL
+		},
+	},
+	"last": {
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1",
+					len(args))
+			}
+
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `last` must be ARRAY, got %s",
+					args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			length := len(arr.Elements)
+			if length > 0 {
+				return arr.Elements[length-1]
+			}
+
+			return NULL
+		},
+	},
+	"rest": {
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1",
+					len(args))
+			}
+
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `rest` must be ARRAY, got %s",
+					args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			length := len(arr.Elements)
+			if length > 0 {
+				newElements := make([]object.Object, length-1)
+				copy(newElements, arr.Elements[1:length])
+				return &object.Array{Elements: newElements}
+			}
+
+			return NULL
+		},
+	},
+	"push": {
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 2 {
+				return newError("wrong number of arguments. got=%d, want=2",
+					len(args))
+			}
+
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `push` must be ARRAY, got %s",
+					args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			length := len(arr.Elements)
+
+			newElements := make([]object.Object, length+1)
+			copy(newElements, arr.Elements)
+			newElements[length] = args[1]
+
+			return &object.Array{Elements: newElements}
+		},
+	},
 }