Fill$-$in the $3$ blank areas of code for the below ML recursive function named rws that takes a string and return a new string with all whitespace removed.

fun rws $\_\_\_\_\_\_\_=$

if s $=""$ then $""$

else if hd $($explode s$)=$ #$""$ then rws$(\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_)$

else implode$($

hd $($explode s$)$ :: explode$(\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_)$

$)$;