There is an important ‘gotcha’ subtlety to this, which occurs when your code both changes the game state (e.g. increments a counter) AND prints something varying according to that change.
This is because Inform needs to be working with an accurate and updated version of what is about to be printed when it expands your text for comparison- otherwise it will be comparing against something that is not what is about to be printed, or against an out-of-date version (i.e. what was printed last time)
For this reason, simply putting a condition to skip ALL the code until something is actually being printed may not work as expected. In the example above, this may lead to problems:
To say jenny desc:
if not expanding text for comparison purposes:
increment flag of Jenny;
if flag of Jenny is 1:
say "Jenny says, 'This is the first time you've seen me.'";
otherwise if flag of Jenny is 2:
say "Jenny says, 'You've seen me before!'";
because now nothing at all is ‘said’ if text is being expanded for comparison purposes- meaning the token is expanded to “”- and Inform may act on this with unexpected responses.
Even this better-looking effort causes difficulty, because the flag is not incremented until something is actually about to be printed, so comparisons run ahead of that are working either with “” (when flag of jenny is 0) or with what was last printed rather than what is about to be printed:
To say jenny desc:
if not expanding text for comparison purposes:
increment flag of Jenny;
if flag of Jenny is 1:
say "Jenny says, 'This is the first time you've seen me.'";
otherwise if flag of Jenny is 2:
say "Jenny says, 'You've seen me before!'";
expands to “” for comparison until ‘This is the first time you’ve seen me.’ is printed, then ‘This is the first time you’ve seen me.’ until ‘You’ve seen me before!’ is printed.
One solution is to increment the flag (or otherwise update the game state) immediately AFTER actually printing something, so any subsequent expansions for comparison are working with updated text, which finally gets printed before the flag is incremented again:
To say jenny desc:
if flag of Jenny is 0:
say "Jenny says, 'This is the first time you've seen me.'";
otherwise if flag of Jenny is 1:
say "Jenny says, 'You've seen me before!'";
if not expanding text for comparison purposes:
increment flag of Jenny;
In even more complicated situations, where it’s absolutely necessary to run the ‘change the game state’ code immediately BEFORE saying the text of a text expansion rather than after saying the last one (because, for example, the code depends on the current location) you may need to maintain a global flag holding the context of the last expansion, so that the game state is changed when expanding for comparison purposes, but ONLY when the last expansion was actually printed (or on the first ever expansion):
last_jenny_desc_expanded_for_comparison_flag is initially false.
To say jenny desc:
if last_jenny_desc_expanded_for_comparison_flag is false:
increment flag of Jenny; [only increment the flag on the first occasion text is ever expanded, or on the first occasion following an actual printing]
if expanding text for comparison purposes:
now last_jenny_desc_expanded_for_comparison_flag is true;
else:
now last_jenny_desc_expanded_for_comparison_flag is false; [record the context of this text expansion, for checking next time]
if flag of Jenny is 1:
say "Jenny says, 'This is the first time you've seen me.'";
otherwise if flag of Jenny is 2:
say "Jenny says, 'You've seen me before!'";
EDIT: This last method is the one used by Inform’s built-in sequential text-modifying expansions such as [one of]...[or]...[or]...[stopping], in order to make sure none of the alternate texts get skipped over for printing due to the text being ‘expanded for comparison purposes’.