if 0 {
Richard Suchenwirth 2004-03-19 - I needed to generate lists of n-tuples from a set, i.e. subsets of fixed length (pairs, triples, ...) in canonical (lexicographic) ordering, like the pairs over {a b c d} being
{a b} {a c} {a d} {b c} {b d} {c d}.Here's code that does that for different values of n:}
proc tuples {n set} {
if {$n == 1} {return $set}
set res {}
incr n -1
foreach i [lrange $set 0 end-$n] {
set set [lrange $set 1 end]
foreach t [tuples $n $set] {
lappend res [linsert $t 0 $i]
}
}
set res
}
% tuples 3 {a b c d}
{a b c} {a b d} {a c d} {b c d}
% tuples 4 {a b c d e}
{a b c d} {a b c e} {a b d e} {a c d e} {b c d e}
% tuples 2 {a b c d}
{a b} {a c} {a d} {b c} {b d} {c d}
