$ sudo apt-get update
$ sudo apt-get install libmlnlffi-smlnj 

libmlnlffi-smlnj is installed in your system.

Make ensure the libmlnlffi-smlnj package were installed using the commands given below,

$ sudo dpkg-query -l | grep libmlnlffi-smlnj *

You will get with libmlnlffi-smlnj package name, version, architecture and description in a table

libmlnlffi-smlnj package basic information: