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if [2013/12/16 05:46]
l
if [2017/10/10 00:39] (current)
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 +<- [[remember|Remembering Things With Variables]] --------- [[nobr|Removing Line Breaks]]->​
 +
 =====<<​if>>​===== =====<<​if>>​=====
  
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 >​%%<<​%%if //​expression//​%%>>​%% //Text// %%<<​%%else if //​expression//​%%>>​%% //Text// ... %%<<​%%endif%%>>​%% >​%%<<​%%if //​expression//​%%>>​%% //Text// %%<<​%%else if //​expression//​%%>>​%% //Text// ... %%<<​%%endif%%>>​%%
  
-//condition// is an [[expression]] that can evaluate to true or false. //Text// is any amount of passage text that you wish to display only if the condition is //true//. <<​endif>>​ is a macro tag indicating the end of the <<​if>>​ macro invocation.+//expression// is an [[expression]] that can evaluate to true or false. //Text// is any amount of passage text that you wish to display only if the condition is //true//. <<​endif>>​ is a macro tag indicating the end of the <<​if>>​ macro invocation.
  
-====Invalid usage====+Note that the //Text// can contain any Twine code, including an inner <<​if>>​ invocation:
  
-You should take care when writing ​<<​if>> ​macros that you write correct expressions, and that you remember what the "and" ​and "or" keywords are capable ​of.+  <<if $body is "​wounded">>​You are <<​if ​$blood <= 5>>about to die<<​else>>​bleeding<<​endif>>​. Seek help!<<​endif>>​ 
 + 
 +====Motivating example==== 
 + 
 +Consider a passage like this: 
 + 
 +> You return to Selator'​s hut. A merry fire is crackling in the kitchen, and something is cooking ​that smells delicious. He greets ​you warmly ​and asks, "Have you got the berry?" ​If you have got the purple berry of the Antherica plant, turn to 175If not, turn to 52. 
 + 
 +(Steve Jackson and Ian Livingstone,​ //Scorpion Swamp//) 
 + 
 +It would be nice if the story could track whether the protagonist found the berry or not, and branch accordingly. We can do this by simply noting the name of the passage where the berry was found:
  
 <​code>​ <​code>​
-<<if $health > 2 and < 4>>+:: Antherica 
 +You have no doubt, from Selator'​s description,​ that you have found the 
 +Antherica plant. Half your mission is completed. Now you must return to the 
 +village with the precious berry.
 </​code>​ </​code>​
-This is invalid because ​the ''>''​ and ''<''​ operators (and indeed, all such operators) require a distinct value to be on both sides of it. In a sense, it is internally interpreted as ''​<<​if ​($health ​2) and ( < 4)>>'',​ which is obviously nonsensical. So, you must rewrite this as ''<<​if $health > 2 and $health < 4>>''​.+ 
 +Then we can use the <<​if>​> macro and the [[function|visited() function]] to display a passage indicating victory:
  
 <​code>​ <​code>​
-<<​if ​$name is "Perone" ​or "Pavone">>​+You return to Selator'​s hut. A merry fire is crackling in the kitchen, and 
 +something is cooking that smells delicious. He greets you warmly and asks, 
 +"Have you got the berry?"​ 
 + 
 +<<​if ​visited("Antherica")>> 
 +"Wonderful!" ​he exclaims... 
 +<<​endif>>
 </​code>​ </​code>​
-This is also invalid, for a different reason: it will be interpreted as ''<<​if ($name is "​Perone"​) or ("​Pavone"​)>>''​ - which is to say, it is true if $name is "​Perone",​ or if the string "​Pavone"​ is not false. This, of course, means that it's always true - an undesirable outcome. You must rewrite it as ''<<​if $name is "​Perone"​ or $name is "​Pavone">>''​.+
  
 ====A note about line breaks==== ====A note about line breaks====
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 (Note: if you prefer, you can also write "else if" as "​elseif"​.) (Note: if you prefer, you can also write "else if" as "​elseif"​.)
 else if else if
 +
 +<- [[remember|Remembering Things With Variables]] --------- [[nobr|Removing Line Breaks]]->​
 +
if.1387172789.txt.gz · Last modified: 2017/10/10 00:37 (external edit)