Category : Miscellaneous Language Source Code
Archive   : PERMUTE1.ZIP
Filename : PERMUTE.SNO

* Recursively defined function to print all permutations of a string
*
* Calling sequence: permute(arg, result)
*
* Arguments (at each level of recursion):
* arg: string to be permuted
* result: used internally to pass intermediate result to next level
* (initially null - omit on initial call)
*
* Local variables (maintained at each level of recursion):
* ch: character of current interest from the argument string
* pre: previous part of original arg string
* post: remaining part of original arg string

define('permute(arg,result)ch,pre,post') :(main)

permute

* Print full result if arg length = 1, and break the recursion

output = eq(size(arg),1) result arg :s(return)

* Otherwise, move through all elements of arg as first element of
* remaining permutation
* Drop to lower level when arg string exhausted

post = arg

loop
post len(1) . ch rem . post :f(return)

* Recursively permute the remaining elements

* Arg passed to next level is current level's original arg,
* less the character of current interest
* Partial result passed to next level is result passed to current
* level, followed by the character of current interest

permute(pre post, result ch)

* Move current character to end of 'pre' string
pre = pre ch :(loop)



* Test the function with keyboard input

main
in = trim(input)
ident(in) :s(end)
permute(in) :(main)

end