**subseq**function in Tally: a string counter gadget produces only contiguous subsequences, e.g. for the sequence

**A B C**it returns

A A B B B C A B CNote that "A C" is missing.The following code produces both contiguous and incontiguous subsequences. It basically assigns N bits to the N elements of the sequence, and uses each element if the bit is 1. The iteration can be done by counting from 1 to pow(2,N)-1, avoiding both trivial cases of the empty and the full sequence.

proc subseq lst { set res {} set max [expr pow(2,[llength $lst])-1] for {set i 1} {$i < $max} {incr i} { set tmp {} foreach bit [bits $i [llength $lst]] el $lst { if $bit {lappend tmp $el} } lappend res $tmp } lsort $res } #-- helper function proc bits {x n} { set res "" while {[llength $res] < $n} { set res "[expr {$x%2}] $res" set x [expr {$x/2}] } return $res }Testing:

% bits 15 5 0 1 1 1 1 % subseq {a b c d} a {a b} {a b c} {a b d} {a c} {a c d} {a d} b {b c} {b c d} {b d} c {c d} d