The current flow of rules in Inform 7 is:
before
instead
check
carry out
after
report

I argue that the most commonly desired insertion point for a new rule
is between the check and carry out rules, and sadly, this is the one
insertion point that is NOT provided. Ideally, you want to make sure
that an action is going to be carried out, and then interrupt it right
before it actually is carried out.

Because this desired insertion point is not provided, you can see many
examples in the manual and in the sample code where the instead hook
is used for this purpose. But this is fragile, and is easily broken,
for example, if you add a chair to your game (see example below).
Therefore, the frequent use of instead rules will ultimately result in
potentially buggy Inform code.

Here, puzzler gmail.com> wrote:

It sounds like what you want to do is write a carry out rule which is
listed before the standard carry out rules.

(I7 isn't really structured in terms of insertion points, but in terms
of rulebooks. Some rulebooks have rules by default, some are empty by
default. Rather than trying to provide a "empty hook" between every
possible pair of steps, the language tries to let you control the
whole sequence.)

I don't see how that would help. Presumably, you mean something like
this:

Carry out entering the green bed for the first time (this is the snake
appearing rule):
say "My goodness there is a snake in the bed!";
move the snake to the green bed;
stop the action.

The snake appearing rule is listed first in the carry out entering
rulebook.

But this doesn't work either. The player still ends up getting into
the bed. The stop the action has no effect. According to the
manual, carry out rules cannot stop the action.

Putting it at the end of the check rules also wouldn't work, because
check rules are forbidden from causing any change.

It really seems that what is needed is a way to make this rule happen
between check and carry out.

On Dec 29, 12:40 am, puzzler gmail.com> wrote:

I tried this code snippet, but it doesn't seem to work. It says the
message "My goodness there is a snake in the bed!", but it doesn't
actually make the snake appear. Am I missing something?

On Dec 29, 12:40 am, puzzler gmail.com> wrote:

I'm not sure where you're getting this, but they certainly *can*: for
example,


A last check entering the green bed for the first time:
say "My goodness there is a snake in the bed!";
move the snake to the green bed instead.


appears to do what you want.

The manual may seem to discourage this, but what it means is that you
usually want to isolate world-model changes that result from
successful action in the carry out rules.

There's also nothing to stop you specifically invoking the check rules
as part of an instead rule, if you wanted. For example, this does what
you want:

"JDC" psu.edu> wrote in message
news:2d210e91-a77f-4b6e-acec-cd1eb4b7a73c@e23g2000prf.googlegroups.com...

Sort of OT here but maybe not....

What you say here is exactly one of the things I find to be a shortcoming of
Inform 7. And even though Andrew says not to think of "hooks" (and I agree)
but instead think of rulebooks, it's still all...

On Dec 29, 11:44 am, "Tatiana" netnews.net> wrote:

I think Graham just wanted to explore that avenue. His paper on it
does make good arguments for it being a valuable effort. It will be
interesting to see what others think though, but I wonder what can of
worms you have opened up by bringing this subject up?

All the best

-James-

"James Jolley" homecall.co.uk> wrote in message
news:e45a6d74-f82b-4423-836f-fa3c83060f0e@x69g2000hsx.googlegroups.com...

I'm not saying that it may not be a valuable effort, at least to try it. But
rule-based systems are not exactly new. They've been tried numerous times
before in various contexts (including programming...

On Dec 29, 4:08 pm, "Tatiana" netnews.net> wrote:

I take your point there. I myself like I7 and what it is trying to
offer folks. There are things I find difficult in it as anyone else
does but it seems rather good at what it offers new users. There
aren't many systems to date that have done so much for newcomers. Look
at the entries in the 2006 comp. Primrose path was written by a
complete newby to Inform as I understood it anyway.