Add file operations

builtins/seek.go

@@ -0,0 +1,37 @@
+package builtins
+
+import (
+	"monkey/object"
+	"monkey/typing"
+	"syscall"
+)
+
+// Seek ...
+func Seek(args ...object.Object) object.Object {
+	if err := typing.Check(
+		"seek", args,
+		typing.RangeOfArgs(1, 3),
+		typing.WithTypes(object.INTEGER_OBJ, object.INTEGER_OBJ, object.INTEGER_OBJ),
+	); err != nil {
+		return newError(err.Error())
+	}
+
+	var (
+		fd     int
+		whence = 0
+	)
+
+	fd = int(args[0].(*object.Integer).Value)
+	offset := args[1].(*object.Integer).Value
+
+	if len(args) == 3 {
+		whence = int(args[2].(*object.Integer).Value)
+	}
+
+	offset, err := syscall.Seek(syscall.Handle(fd), offset, whence)
+	if err != nil {
+		return newError("IOError: %s", err)
+	}
+
+	return &object.Integer{Value: offset}
+}