tasks a-s

Task/Permutations/Seed7/permutations.seed7

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+$ include "seed7_05.s7i";
+
+const type: permutations is array array integer;
+
+const func permutations: permutations (in array integer: items) is func
+  result
+    var permutations: permsList is 0 times 0 times 0;
+  local
+    const proc: perms (in array integer: sequence, in array integer: prefix) is func
+      local
+        var integer: element is 0;
+        var integer: index is 0;
+      begin
+        if length(sequence) <> 0 then
+          for element key index range sequence do
+            perms(sequence[.. pred(index)] & sequence[succ(index) ..], prefix & [] (element));
+          end for;
+        else
+          permsList &:= prefix;
+        end if;
+      end func;
+  begin
+    perms(items, 0 times 0);
+  end func;
+
+const proc: main is func
+  local
+    var array integer: perm is 0 times 0;
+    var integer: element is 0;
+  begin
+    for perm range permutations([] (1, 2, 3)) do
+      for element range perm do
+        write(element <& " ");
+      end for;
+      writeln;
+    end for;
+  end func;