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=={{header|Quackery}}==
===General Solution===
The word ''perms'' solves a more general task; generate permutations of between ''a'' and ''b'' items (inclusive) from the specified nest.
kucq kuca kaq kaqu kaqc kau kauq kauc kac kacq
kacu kcq kcqu kcqa kcu kcuq kcua kca kcaq kcau</pre>
===An Uncommon Ordering===
The central idea is that given a list of the permutations of say 3 items, each permutation can be used to generate 4 of the permutations of 4 items, so for example, from <code>[ 2 0 1 ]</code> we can generate
::<code>[ 3 2 0 1 ]</code>
::<code>[ 2 3 0 1 ]</code>
::<code>[ 2 0 3 1 ]</code>
::<code>[ 2 0 1 3 ]</code>
by stuffing the 3 into each of the 4 possible positions that it could go.
The code start with a nest of all the permutations of 0 items <code>[ [ ] ]</code>, and each time though the outer <code>times</code> loop (i.e. 4 times in the example) it takes each of the permutations generated so far (this is the <code>witheach</code> loop) and applies the central idea descried above (that is the inner <code>times</code> loop.)
'''Some aids to reading the code.'''
Quackery is a stack based language. If you are unfamiliar the with words <code>swap</code>, <code>rot</code>, <code>dup</code>, <code>2dup</code>, <code>dip</code>, <code>unrot</code> or <code>drop</code> they can be skimmed over as "noise" to get a gist of the process.
<code>[]</code> creates an empty nest <code>[ ]</code>.
<code>times</code> indicates that the word or nest following it is to be repeated a specified number of times. (The specified number is on the top of the stack, so <code>4 times [ ... ]</code>repeats some arbitrary code 4 times.
<code>i</code> returns the number of times a <code>times</code> loop has left to repeat. It counts down to zero.
<code>i^</code> returns the number of times a <code>times</code> loop has been repeated. It counts up from zero.
<code>size</code> returns the number of items (words, numbers, nests) in a nest.
<code>witheach</code> indicates that the word or nest following it is to be repeated once for each item in a specified nest, with successive items from the nest available on the top of stack on each repetition.
<code>999 ' [ 10 11 12 13 ] 3 stuff</code> will return <code>[ 10 11 12 99 13 ]</code>by stuffing the number 99 into the 3rd position in the nest. (The start of a nest is the zeroth position, the end of this nest is the 5th position.)
<code>nested join</code> adds a nest to the end of a nest as its last item.
=={{header|Quackery}}==
<lang Quackery> [ ' [ [ ] ] swap times
[ [] i rot witheach
[ dup size 1+ times
[ 2dup i^ stuff
dip rot nested join
unrot ] drop ] drop ] ] is perms ( n --> [ )
4 perms witheach [ echo cr ]
</lang>
{{out}}
<pre>[ 0 1 2 3 ]
[ 1 0 2 3 ]
[ 1 2 0 3 ]
[ 1 2 3 0 ]
[ 0 2 1 3 ]
[ 2 0 1 3 ]
[ 2 1 0 3 ]
[ 2 1 3 0 ]
[ 0 2 3 1 ]
[ 2 0 3 1 ]
[ 2 3 0 1 ]
[ 2 3 1 0 ]
[ 0 1 3 2 ]
[ 1 0 3 2 ]
[ 1 3 0 2 ]
[ 1 3 2 0 ]
[ 0 3 1 2 ]
[ 3 0 1 2 ]
[ 3 1 0 2 ]
[ 3 1 2 0 ]
[ 0 3 2 1 ]
[ 3 0 2 1 ]
[ 3 2 0 1 ]
[ 3 2 1 0 ]
</pre>
=={{header|R}}==
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