Permutations: Difference between revisions

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 perms([1, 2, 3]) // [[1, 2, 3], [2, 1, 3], [3, 1, 2], [1, 3, 2], [2, 3, 1], [3, 2, 1]]</lang>
+=={{header|Tailspin}}==
+<lang tailspin>
+templates permutations
+  <1> [1] !
+  <>
+    def n: $it
+    templates expand
+      def p: $it
+..$n -> (def k: $it
+        [$p(1..$k-1)..., $n, $p($k..-1)...] !) !
+    end expand
+    $n - 1 -> permutations -> expand !
+end permutations
+def alpha: ['ABCD'...]
+[ $alpha::length -> permutations -> '$($alpha($it)...)' ] -> stdout
+</lang>
+{{out}}
+<pre>
+[DCBA, CDBA, CBDA, CBAD, DBCA, BDCA, BCDA, BCAD, DBAC, BDAC, BADC, BACD, DCAB, CDAB, CADB, CABD, DACB, ADCB, ACDB, ACBD, DABC, ADBC, ABDC, ABCD]
+</pre>
+With a little more careful work we can output permutations in lexical order
+<lang tailspin>
+templates lexicalPermutations
+  <1> [1] !
+  <>
+    def n: $it
+    def p: [ $n - 1 -> lexicalPermutations ]
+..$n -> (def k: $it
+      def tail: [1..$n -> (<~$k> $it !)]
+      $p... -> [ $k, $tail($it)...] !) !
+end lexicalPermutations
+def alpha: ['ABCD'...]
+[ $alpha::length -> lexicalPermutations -> '$($alpha($it)...)' ] -> stdout
+</lang>
+{{out}}
+<pre>
+[ABCD, ABDC, ACBD, ACDB, ADBC, ADCB, BACD, BADC, BCAD, BCDA, BDAC, BDCA, CABD, CADB, CBAD, CBDA, CDAB, CDBA, DABC, DACB, DBAC, DBCA, DCAB, DCBA]
+</pre>
 =={{header|Tcl}}==