Help unborking an untying rule

Authoring Inform 7
1

Either I am going mad, or I already am, because I cannot for the life of me figure out why this code won’t compile:

A thing can be knotted or unknotted.  A thing is usually unknotted.

Understand the command "untie" as something new.  Understand "untie [thing]" as untying it.  Untying it is an action applying to one thing.  

Check untying it:
	If the noun is not knotted, say "No knot there!" instead.
	
The yarn is an object in the bedroom.  The yarn is knotted.

After untying the yarn:
	Now the yarn is unknotted.

The After rule throws up a compiler error, saying that “untying the yarn” doesn’t make sense as a description of an action. But it sure seems like it is when I comment out that rule and use ACTIONS to see how the parser understands UNTIE YARN. I must be overlooking something incredibly basic, but I can’t for the life of me find it. Thanks much for any assistance!

2

Take “it” out of the action definition and the Understand line.

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3

Thank you!

(This presumably doesn’t mean much coming from me, clearly a dummy on the evidence above, but Hadean Lands was beyond brilliant).

4

This is confusing because if you define an action applying to two things, you should use “it”.

Inserting it into is an action applying to two things.

But for a one-thing action, “it” causes problems.

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5

Yeah, I defined untying by analogy to tying it to – cargo cult logic led me astray.

6

A further improvement you can make to this is to replace the above with:

Carry out untying:
	now the noun is unknotted.

Report untying:
	say "You carefully un-knot [the noun]."

(After rules are really intended for story-specific overrides that happen between Carry Out and Report and stop the latter from happening. Default behaviour for actions – even story-specific ones – should ideally be defined solely with Check, Carry Out, and Report. That way you can use the other rulebooks for special cases.)

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7

Thanks Gavin! That is more or less how I had it set up, before I started to try to break out specific cases to see if that helped with the debugging process.