===== <> ===== ====Motivating example=== [[Variable]]s are a good way to keep track of what a reader has chosen in a story, or to manage some other part of the story state. For example, many gamebooks start off with something like this: > All you possess is an Axe (note under Weapons on your Action Chart) and a Backpack containing 1 Meal (note under Meals on your Action Chart). (Joe Dever, //Flight from the Dark//) You can keep track of the number of meals that the protagonist carries with the [[<>]] macro, like so:


All you possess is an Axe and a Backpack containing 1 Meal.
<>

Later on in the story, you can change the value of a variable with another ''<>'' statement.


You are feeling tired and hungry and you must stop to eat. <>

If you make a mistake with ''<>'', a pink highlighted message will appear where you invoked it. Here's a sample error message, in this case forgetting the sigil before the variable ''$meals'':


bad expression: meals is not defined

====Setter operators ==== The ''to'' and ''-='' are special operators called **setter operators** - while [[expression]]s may contain comparison operators like ''+'' or ''not'', setter operators are commands to modify the values of variables. The ''-='' operator lowers the variable on the left by the value on the right. There is also a ''+='' operator that does the opposite. The most useful setter operators are as follows: ^ Operator(s) ^ Function ^ Example ^ | to, = | Sets the variable on the left to the value on the right | ''$bullets to 5'' | | += | Increases the variable on the left by the number on the right, OR adds the string on the right to the end of the variable. ''$var += 1'' is shorthand for ''$var to $var + 1'' | ''$dogs += 2'' | | -= | Decreases the variable on the left by the number on the right. ''$var -= 1'' is shorthand for ''$var to $var - 1'' | ''$health -= 2'' | | *= | Multiplies the variable on the left by the number on the right. ''$var *= 2'' is shorthand for ''$var to $var * 2'' | ''$shields *= 2'' | | /= | Divides the variable on the left by the number on the right. ''$var /= 2'' is shorthand for ''$var to $var / 2'' | ''$coins /= 2'' | ====Multiple operations in one <> ==== When you have multiple <> macro tags next to one another, you can replace them with a shorthand that uses only one <>. Simply take the operations in each instance, and join them together using either commas or semicolons. For instance, these three macro tags:

<>
<>
<>

...can be changed to just this: <> ====A note about <> and links==== It is easy to assume that the placement of links in a passage has some bearing on what the game's variable state will be once you click it:


/% The following code is ineffectual %/
<>
[[The lamp is red]]
<>
[[The lamp is blue]]

But this is erroneous! All of these [[<>]] macros are run as soon as the passage is displayed, in order. Clicking the "The lamp is red" link won't cause the <> tag to not have happened. To achieve the desired effect in the above passage, you should use [[link|setter links]]:


[[The lamp is red][$lamp = "red"]]
[[The lamp is blue][$lamp = "blue"]]