When to use which action processing rules

[Zed (Zed Lopez)]

check eating the rock: say "You can't eat that!" instead

This is how I do it.

In my ever-humble opinion, if Instead rules can be avoided they should be avoided. Which sounds harsh, so try this if you prefer: use Instead rules only when they’re the most appropriate choice.

Likely cases for Before rules:

• you’re redirecting to another action
• the visibility/accessibility/carrying requirement rules don’t need to be checked prior to your rule

Likely cases for Instead rules: you want to test something and potentially end the action in failure and it’s appropriate for this rule to run after the visibility, accessibility, carrying requirement rules but before any Check rules, and you’re using an action pattern or a kind of action.

The name action pattern appears just once in the docs (buried in the Day One example) but it’s the name for things like:

• doing something to the cucumber sandwich
• doing something other than examining, taking or dropping with the dagger

Given Kissing Mr Carr is unmaidenly behavior, then unmaidenly behavior is a kind of action. “kind” in “kind of action” has nothing to do with what “kind” means everywhere else in Inform and these would better be called named action patterns (or at least that’d be an improvement if the term action pattern itself were better known). @drpeterbatesuk wrote a treatise on action patterns.

Each of Before, After, and Instead is a rulebook. But for each action name there’s a distinct Check, Carry Out, Report rulebook, e.g., Check taking, Check dropping, etc. So you can’t make Check rules for action patterns, named or otherwise.

If you want to test something and potentially end the action in failure and you’re not changing the world state and the rule’s about a distinct action name, not an action pattern, I’d very highly recommend a Check rule.

Now, it’s not necessarily terrible to use an Instead rule instead of a Check rule for that case. I’ll note, though, that my philosophy on errors is that if an action is impossible for several reasons, it’s most appropriate for the game to balk at the most egregiously ridiculous one. If you try to put a bag inside itself, I think “you can’t put something inside itself” makes a better error message than, say, “that seems to belong to…” (and this is, in fact, the default behavior). So I usually want some new potentially-reject-action rule to come after some of the Check rules which, of course, would be impossible if it were an Instead rule.

The thing I’d really jump up and down and scream Don’t do this! about is basically coding the whole action within an Instead rule, a thing that happens repeatedly in the examples. I think that sets a problematic, um, example.

But don’t take my word for it. I once made a collection of Instead rule regrets. Besides those in this thread…

I have 271 instead rules and it is confusing

This is probably a question for the quite experienced Inform programmers. In Inform I am gradually learning to appreciate the different tabs. I’ve been using the index tab for a while, but the rules tab only recently. In the game I’m working on right now, I have 24 before rules, 18 after rules, and 271 instead rules. The instead rules are cluttered as a result and therefore it feels a bit wrong. I wonder: Should I do it differently? Should I create special rule books and sort (at least so…

@DeusIrae

I think the main [mistake or crutch for those starting out] is overuse of Instead rules, and corresponding neglect of Check, Carry Out, etc. rules (a related but more venial sin is cramming everything an action does into a single rule rather than using check, report, before, after, etc. when it’d be helpful to do so).

@kamineko

I spent maybe two months working on my first two rooms–to be fair, there were verbs and tables, too–and a big chunk of that was reworking all of the “instead” and “before” stuff into the “check, carry out, report” idiom. It was worthwhile, of course. The code was much easier to read and troubleshoot, and this approach allowed me to better leverage values and kinds.

@BlueAskew

DeusIrae mentioned the overuse of instead rules (an excellent point), which is something many have had experience with. I’m no exception. Instead rules are so easy to overuse because the naturalness of their phrasing somewhat obscures what they actually do - the role they play in action processing. I really only stopped overuseing them when I understood that role through the framework of rules. The chapter on rules honestly blew my mind the first time I read it.

@AmandaB

I have a strange and unwise attraction to that very bad boy of Inform 7: “instead of”.

I had an “instead of” rule that I wisely changed to a “check” rule, but failed to take out the “if the player carries the paper” that made the instead rule work as I needed. It sucks to have such a reflexive tendency to use the very thing that will always, ALWAYS cause me grief.

@Juniper200

I wanted to pop in and say that redoing one of my puzzles with Check rules instead of my many, many nested Instead rules worked like a charm. Lesson learned!

@EpicIFer

Instead rules can be so tricky and can have unpredictable(?) results because we tend to assume the player can actually ‘do’ the action described without considering possible limitations which may not be all that obvious. I’ve had so many laughable results with Instead rules.
[…]
Always best to have an action go through its Checks or have Check rules in place for unique results. I find it’s best to have an Instead rule either only ‘say’ something, only ‘try’ something else, or both, unless it’s absolutely clear that there are no limitations blocking the action.

I know I’ve seen more, but I gave up searching after that.

You know how many times I’ve seen someone say “Jeez, I used too many Check rules and now my code is an incomprehensible mess. I wish I’d used more Instead rules” ?

Zero.