gistfile1.sml

fun max_eff (xs : int list) : int option =
    if null xs
    then NONE
    else
	let
	    fun max_nonempty (xs : int list) : int =
		if null (tl xs)
		then hd xs
		else
		    let
			val hd  = hd xs
			val ans = max_nonempty (tl xs)
		    in
			if hd > ans
			then hd
			else ans
		    end
	in
	    SOME (max_nonempty xs)
	end