first attempt

src/core/List.pm

@@ -532,6 +532,33 @@ my class List does Positional { # declared in BOOTSTRAP
     method STORE_AT_POS(Int \pos, Mu \v) is rw {
         nqp::bindpos($!items, nqp::unbox_i(pos), v)
     }
+
+    my sub combinations(Int $n, Int $k) {
+	return [] if $k == 0;
+	return () if $k > $n;
+	gather {
+	    take [0, (1..^$n)[@$_]] for combinations($n-1, $k-1);
+	    take [(1..^$n)[@$_]]    for combinations($n-1, $k  );
+	}
+    }
+    proto method combinations($) {*}
+    multi method combinations( Int $of ) {
+	gather take self[@$_] for combinations self.elems, $of
+    }
+    multi method combinations( Range $of = 0 .. * ) {
+	X::NYI.new.throw;
+    }
+
+    my sub permutations(Int $n) {
+	$n == 1 ?? ( [0,] ) !!
+	gather for ^$n -> $i {
+	    my @i = grep none($i), ^$n;
+	    take [$i, @i[@$_]] for permutations($n - 1);
+	}
+    }
+    method permutations() {
+	gather take self[@$_] for permutations self.elems;
+    }
 }
 
 sub eager(|) {