lab3.xml

fun thenAddOne (f,ys:int)=f ys + 1;
fun pow2 ys=ys*ys;
thenAddOne (pow2,2);

fun maplist(f,[])=[]
	|	maplist(f,y::ys)=f y :: maplist(f,ys);
	
fun maplist(f,xs)=map f xs;
maplist(pow2,[2,3,4,5]);

fun maplist' f  = 
	let fun f1(xs)=map f xs;
	in f1 end;
maplist' pow2 [2,3,4,5];
	
fun findOdd [] = NONE
	| findOdd (y::ys) = 
		if ((y mod 2) = 1) then SOME(y) else findOdd ys;


		
fun subsetSumOption (x,s)=
	let     
	fun subset_sum ([] : int list, s : int) : bool * int list =
		if s = 0 then (true, [])
		else (false, [])
	| subset_sum (_ : int list, 0 : int) : bool * int list = (true, [])
	| subset_sum (x::xs : int list, s : int) : bool * int list =
		let val ((w,wList),(wo,woList)) =
		(subset_sum(xs, s-x), subset_sum(xs, s)) in
			case (w,wo) of
			(true,_) => (true, x::wList)
		| (_,tru   e) => (true, woList)
        | (_,_) => (false, [])
		end;
	fun re_2(x,y)=
		if(x) then SOME(y) else NONE 
	in 
	re_2(subset_sum(x,s))
	end;
	
	
fun exists f = foldl f false xy; 

fun panduan x = 
	if(x=2) then true else false;
	
exists panduan [1,3,4];

fun forall f xy = foldl f true;
		
datatype 'a tree = Empty 
|	Node of 'a tree * 'a * 'a tree;

fun treeFilter(f)=
	let fun tF(Empty)=Empty
	|	tF(Node(A,x,B))=
		if(f(x)) then Node(tF(A),SOME(x),tF(B))
		else Node(tF(A),NONE,tF(B))
	in tF end;