This is the code I wrote
Code:
on *:TABCOMP:#: {
  if ( $nick($chan,$1) != $null ) || ( $nick($chan,$left($1,$calc($len($1)-1))) != $null ) { 
    if ( $right($1,1) == $chr(44) ) { 
      /editbox -a left($1,1)
    }
    else {
      /editbox -ap $1 $+ $chr(44)
    }
    haltdef
  }
}


Problem is that I can't retrieve what was typed before TAB was pressed in the ON TABCOMP, and to cycle nicks one need to double tap TAB for the next one to show.