Cartesian product of two or more lists: Difference between revisions

=={{header|Standard ML}}==

<lang sml>fun prodList (nil, _) = nil

| prodList ((x::xs), ys) = map (fn y => (x,y)) ys @ prodList (xs, ys)

fun naryProdList zs = foldl (fn (xs, ys) => map op:: (prodList (xs, ys))) [[]] (rev zs)</lang>

{{out}}

<pre>- prodList ([1, 2], [3, 4]);

val it = [(1,3),(1,4),(2,3),(2,4)] : (int * int) list

- prodList ([3, 4], [1, 2]);

val it = [(3,1),(3,2),(4,1),(4,2)] : (int * int) list

- prodList ([1, 2], []);

stdIn:8.1-8.22 Warning: type vars not generalized because of

value restriction are instantiated to dummy types (X1,X2,...)

val it = [] : (int * ?.X1) list

- naryProdList [[1776, 1789], [7, 12], [4, 14, 23], [0, 1]];

val it =

[[1776,7,4,0],[1776,7,4,1],[1776,7,14,0],[1776,7,14,1],[1776,7,23,0],

[1776,7,23,1],[1776,12,4,0],[1776,12,4,1],[1776,12,14,0],[1776,12,14,1],

[1776,12,23,0],[1776,12,23,1],[1789,7,4,0],[1789,7,4,1],[1789,7,14,0],

[1789,7,14,1],[1789,7,23,0],[1789,7,23,1],[1789,12,4,0],[1789,12,4,1],

[1789,12,14,0],[1789,12,14,1],[1789,12,23,0],[1789,12,23,1]]

: int list list

- naryProdList [[1, 2, 3], [30], [500, 100]];

val it = [[1,30,500],[1,30,100],[2,30,500],[2,30,100],[3,30,500],[3,30,100]]

: int list list

- naryProdList [[1, 2, 3], [], [500, 100]];

val it = [] : int list list</pre>