Question

Define a function in SML, called "less" of type int * int list -> int list so that less(e,L) is a list of all the integers in L that are less than e.

Answer 1

/* Lets Describing a function member of type ''a ''a list -> bool
so that member(e, L) is true if and only if e is an element of the given list L. *)

(/* Correct, but non-pattern matching version is :
fun member (e, L) =
if null L
then false
else if e = hd(L)
then true
else member (e, tl(L));
/*)

fun member (e, nil) = false
| member (e, y::ys) = if (e=y)
then true
else member(e, ys);

member (1, []);
member (1, [1, 2]);
member (1, [2, 1, 3]);
member (1, [2, 3]);

(/ Describing a function less of type int int list -> int list
so that less (e, L) is a list of all the integers in L that
are less than e
/*)

(*/ Correct, but non-pattern matching version:
fun less (e, L) =
if null L
then nil
else if hd(L) < e
then hd(L) :: less(e, tl(L))
else less (e, tl(L));
*)

fun less (e, nil) = nil
| less (e, y::ys) = if y < e
then y :: less(e, ys)
else less (e, ys);

(*/ Define a function repeats of type ''a list -> bool so that
repeats (L) is true if and only if the list L has two equal
elements next to each other
*)

(*/ Correct, but non-pattern matching version:
fun repeats (L) =
if null L or else null(tl(L))
then false
else if hd(L) = hd(tl(L)) then true
else repeats (tl(L));
*)

fun repeats (nil) = false
| repeats (y::nil) = false
| repeats (y::ys) = if y = hd(ys) then true
else repeats(ys);