A thing can have a rule as a property, if we like. Here we are going to allow the player to make a soup whose effects will depend on its ingredients. Each ingredient will have its own "food effect" rule, to be followed when the food is eaten.
Note that there are other, slightly less cumbersome ways to do the same thing -- we will see in the chapter on Rulebooks that we could make a "food effects rulebook" and then write a number of rules such as "food effects rule for carrots" or "food effects rule for the stone". Nonetheless, we demonstrate rules-as-properties here for the sake of thoroughness.
So:
{*}"Stone"
A food is a kind of thing that is edible. A food has a rule called the food effect.
Carry out eating a food:
if a food is part of the noun:
repeat with item running through things which are part of the noun:
if item is a food, follow the food effect of the item;
{**}Some carrots are a food. The food effect of carrots is the bright-eye rule. This is the bright-eye rule: now the player is bright-eyed.
Some potatoes are a food. The food effect of the potatoes is the sleepiness rule. This is the sleepiness rule: now the player is sleepy.
The broth is a food. The indefinite article of the broth is "some". The food effect of broth is the filling rule. This is the filling rule: now the player is full.
The hambone is a food. The food effect of the hambone is the heartiness rule. This is the heartiness rule: now the player is strong. Instead of eating the hambone: say "You cannot just eat a bone!"
The poison ivy is a food. "Poison ivy grows nearby." The food effect of poison is the illness rule. This is the illness rule: now the player is ill.
A person can be bright-eyed or blind. The player is blind.
A person can be well or ill. The player is well.
A person can be hungry or full. The player is full.
A person can be strong or weak. The player is weak.
A person can be awake or sleepy. The player is sleepy.
The broth is in the kettle. The kettle is on the fire. The fire is in the Clearing. The Clearing is a room.
The player carries the hambone, the potatoes, and the carrots. The ivy is in the clearing.
Instead of examining the broth:
if something is part of the broth, say "In the broth, [a list of things that are part of the broth] float[if exactly one thing is part of the broth]s[end if].";
otherwise say "It is just a thin broth with no other ingredients."
Test me with "x broth / eat hambone / put hambone in kettle / x broth / put potatoes in broth / x broth / eat carrots / eat broth / put ivy in kettle / eat ivy".