diff --git a/evaluator/builtins.go b/evaluator/builtins.go
index 3c1a4b0..174f75a 100644
--- a/evaluator/builtins.go
+++ b/evaluator/builtins.go
@@ -1,7 +1,9 @@
 package evaluator
 
 import (
+	"bufio"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"strconv"
 	"strings"
@@ -314,4 +316,124 @@ var builtins = map[string]*object.Builtin{
 			}
 		},
 	},
+
+	"open": {
+		Fn: func(file string, line int, args ...object.Object) object.Object {
+			if len(args) != 2 {
+				return newError("wrong number of arguments. got=%d, want=2", file, line, len(args))
+			}
+			if args[0].Type() != object.STRING_OBJ {
+				return newError("argument to `open` must be STRING, got %s", file, line, args[0].Type())
+			}
+			if args[1].Type() != object.STRING_OBJ {
+				return newError("argument to `open` must be STRING, got %s", file, line, args[1].Type())
+			}
+			filename := args[0].(*object.String).Value
+			mode := args[1].(*object.String).Value
+			var flag int
+			switch mode {
+			case "r":
+				flag = os.O_RDONLY
+			case "w":
+				flag = os.O_WRONLY | os.O_CREATE
+			case "a":
+				flag = os.O_WRONLY | os.O_APPEND | os.O_CREATE
+			default:
+				return newError("invalid mode %s", file, line, mode)
+			}
+			openedFile, err := os.OpenFile(filename, flag, 0644)
+			if err != nil {
+				return newError("could not open file %s", file, line, filename)
+			}
+			return &object.File{File: openedFile}
+		},
+	},
+	"close": {
+		Fn: func(file string, line int, args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1", file, line, len(args))
+			}
+			if args[0].Type() != object.FILE_OBJ {
+				return newError("argument to `close` must be FILE, got %s", file, line, args[0].Type())
+			}
+			fileObj := args[0].(*object.File)
+			err := fileObj.File.Close()
+			if err != nil {
+				return newError("could not close file %s", file, line, fileObj.File.Name())
+			}
+			return NULL
+		},
+	},
+	"read": {
+		Fn: func(file string, line int, args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1", file, line, len(args))
+			}
+			if args[0].Type() != object.FILE_OBJ {
+				return newError("argument to `read` must be FILE, got %s", file, line, args[0].Type())
+			}
+			fileObj := args[0].(*object.File)
+			content, err := ioutil.ReadAll(fileObj.File)
+			if err != nil {
+				return newError("could not read file %s", file, line, fileObj.File.Name())
+			}
+			return &object.String{Value: string(content)}
+		},
+	},
+	"write": {
+		Fn: func(file string, line int, args ...object.Object) object.Object {
+			if len(args) != 2 {
+				return newError("wrong number of arguments. got=%d, want=2", file, line, len(args))
+			}
+			if args[0].Type() != object.FILE_OBJ {
+				return newError("argument to `write` must be FILE, got %s", file, line, args[0].Type())
+			}
+			if args[1].Type() != object.STRING_OBJ {
+				return newError("argument to `write` must be STRING, got %s", file, line, args[1].Type())
+			}
+			fileObj := args[0].(*object.File)
+			_, err := fileObj.File.WriteString(args[1].(*object.String).Value)
+			if err != nil {
+				return newError("could not write to file %s", file, line, fileObj.File.Name())
+			}
+			return NULL
+		},
+	},
+	"readline": {
+		Fn: func(file string, line int, args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1", file, line, len(args))
+			}
+			if args[0].Type() != object.FILE_OBJ {
+				return newError("argument to `readline` must be FILE, got %s", file, line, args[0].Type())
+			}
+			fileObj := args[0].(*object.File)
+			content, err := bufio.NewReader(fileObj.File).ReadString('\n')
+			if err != nil {
+				return newError("could not read file %s", file, line, fileObj.File.Name())
+			}
+			return &object.String{Value: content}
+		},
+	},
+	"readlines": {
+		Fn: func(file string, line int, args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1", file, line, len(args))
+			}
+			if args[0].Type() != object.FILE_OBJ {
+				return newError("argument to `readlines` must be FILE, got %s", file, line, args[0].Type())
+			}
+			fileObj := args[0].(*object.File)
+			content, err := ioutil.ReadAll(fileObj.File)
+			if err != nil {
+				return newError("could not read file %s", file, line, fileObj.File.Name())
+			}
+			var elements []object.Object
+			for _, line := range strings.Split(string(content), "\n") {
+				elements = append(elements, &object.String{Value: line})
+			}
+
+			return &object.Array{Elements: elements}
+		},
+	},
 }
diff --git a/object/object.go b/object/object.go
index ed2e9fb..d1d3e14 100644
--- a/object/object.go
+++ b/object/object.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"hash/fnv"
+	"os"
 	"strconv"
 	"strings"
 	"unicode/utf8"
@@ -35,6 +36,7 @@ const (
 	BUILTIN_OBJ = "BUILTIN"
 	QUOTE_OBJ   = "QUOTE"
 	MACRO_OBJ   = "MACRO"
+	FILE_OBJ    = "FILE"
 )
 
 type Boolean struct {
@@ -265,3 +267,10 @@ type Float struct {
 
 func (f *Float) Inspect() string  { return strconv.FormatFloat(f.Value, 'f', -1, 64) }
 func (f *Float) Type() ObjectType { return FLOAT_OBJ }
+
+type File struct {
+	File *os.File
+}
+
+func (f *File) Inspect() string  { return f.File.Name() }
+func (f *File) Type() ObjectType { return FILE_OBJ }