Add file operations

builtins/read.go

@@ -0,0 +1,40 @@
+package builtins
+
+import (
+	"monkey/object"
+	"monkey/typing"
+	"syscall"
+)
+
+// DefaultBufferSize is the default buffer size
+const DefaultBufferSize = 4096
+
+// Read ...
+func Read(args ...object.Object) object.Object {
+	if err := typing.Check(
+		"read", args,
+		typing.RangeOfArgs(1, 2),
+		typing.WithTypes(object.INTEGER_OBJ, object.INTEGER_OBJ),
+	); err != nil {
+		return newError(err.Error())
+	}
+
+	var (
+		fd int
+		n  = DefaultBufferSize
+	)
+
+	fd = int(args[0].(*object.Integer).Value)
+
+	if len(args) == 2 {
+		n = int(args[1].(*object.Integer).Value)
+	}
+
+	buf := make([]byte, n)
+	n, err := syscall.Read(syscall.Handle(fd), buf)
+	if err != nil {
+		return newError("IOError: %s", err)
+	}
+
+	return &object.String{Value: string(buf[:n])}
+}