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---
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language: Inform7
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contributors:
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- ["Hyphz", "http://github.com/hyphz/"]
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filename: LearnInform.Inform
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---
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Inform 7 is a natural language based language created by Graham Nelson and Emily Short for writing text adventures, but also potentially usable for other text based applications, especially data backed ones.
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```
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"LearnInform" by Hyphz
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[This is a comment.]
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[Inform 7 is a language designed for building text adventures.
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It can be used for other purposes too, although the default
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library builds a text adventure. Inform 7 is object oriented.]
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[This creates a class by subclassing. "Value" is the universal subclass,
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but "object" is the most basic that behaves like an OO object.]
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A datablock is a kind of object.
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[Classes can have properties.]
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A datablock can be broken. [This creates a boolean property.]
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A datablock is usually not broken. [This sets its default value.]
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A datablock can be big or small. [This creates an enumerated property.]
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A datablock is usually small. [This sets its default value.]
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A datablock has a number called the sequence number. [This creates a typed property.]
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A datablock has some text called the name. ["Some text" means a string.]
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A datablock has a datablock called the chain. [Declared classes become types.]
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[This creates a global named instance.]
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Block1 is a datablock.
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The sequence number of Block1 is 1.
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The name of Block1 is "Block One."
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[Functions and procedures are defined as "phrases".]
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To do the thing everyone does with their first program:
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say "Hello World.". [Full stop indicates the end, indent indicates the scope.]
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To dump (the block - a datablock): [That's how we create a parameter.]
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say the sequence number of the block;
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say the name of the block;
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if the block is broken, say "(Broken)".
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To toggle (the block - a datablock):
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if the block is broken: [Conditional.]
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now the block is not broken; [Updating a property.]
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else:
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now the block is broken.
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[Multiple parameters.]
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To fix (the broken block - a datablock) using (the repair block - a datablock):
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if the broken block is not broken, stop; [Comma for a non indented single command.]
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if the repair block is broken, stop;
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now the sequence number of the broken block is the sequence number of the repair block;
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now the broken block is not broken.
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[Because of its text adventure origins, Inform 7 doesn't generally allow objects
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to be created dynamically, although there's a language extension that enables it.]
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Block2 is a datablock.
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Block2 is broken.
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The sequence number of Block2 is 2.
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The name of Block2 is "Block two."
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To demonstrate calling a phrase with two parameters:
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Let the second block be block2; [Local pointer variable.]
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fix the second block using Block1;
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say the sequence number of the second block. [1.]
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[Lists.]
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To show how to use list types:
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let the list be a list of datablocks;
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add Block1 to the list;
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add Block2 to the list;
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say the list; ["Block1 and Block2"]
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[Membership.]
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if Block1 is listed in the list:
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say "Block1 is there.";
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[Loop.]
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repeat with the block running through the list:
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dump the block; [1 Block One. 1 Block Two.]
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[Remember block two's sequence number was changed above.]
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let X be entry 2 of the list; [Counting starts at 1.]
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dump X; ["1 Block two."]
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remove X from the list;
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say the list. [Block1]
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[Here's how we define a function and do arithmetic.]
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To decide which number is the sum of all numbers up to (X - a number) (this is summing up):
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let the total so far be a number;
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repeat with the current number running from 1 to X:
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now the total so far is the total so far + the current number;
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decide on the total so far. [This is the return statement.]
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[ We have higher order functions too. ]
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To demonstrate a higher order function:
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say summing up applied to {1, 2, 3, 4}.
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To decide which number is the result of applying (phrase - phrase A -> A) twice to (B - a value of kind A):
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let b1 be phrase applied to B;
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let b2 be phrase applied to b1;
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decide on b2.
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To demonstrate defining a higher order function:
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let X be 5;
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say the result of applying summing up twice to X.
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[ Rulebooks allow a number of functions which apply to the same type under different conditions to be stacked. ]
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Datablock validation rules is a datablock based rulebook.
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A datablock validation rule for a broken datablock: rule fails.
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A datablock validation rule for a datablock (called the block):
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dump the block;
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rule succeeds.
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To demonstrate invoking a rulebook:
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follow datablock validation rules for Block1;
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follow datablock validation rules for Block2.
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[ Objects can also have relations, which resemble those in a relational database. ]
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A dog is a kind of thing.
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Rover is a dog.
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The kennel is a container. [This is a built in base class.]
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Rover is in the kennel. [This creates an inbuilt relation called "containment".]
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[We can create relations by declaring their type.]
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Guide dog ownership relates one dog to one person. [One-to-one.]
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Property ownership relates various things to one person. [Many-to-one.]
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Friendship relates various people to various people. [Many-to-many.]
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[To actually use them we must assign verbs or prepositions to them.]
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The verb to own means the property ownership relation.
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The verb to be the guide dog of means the guide dog ownership relation.
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The verb to be guided by means the reversed guide dog ownership relation.
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The verb to be friends with means the friendship relation.
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Edward is a person. A person can be blind. Edward is blind.
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Edward is guided by Rover.
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Benny is a person. Edward is friends with Benny.
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To demonstrate looking something up with a relation:
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repeat with the dog running through things that are the guide dog of Edward:
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say the dog;
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repeat with the friend running through things that are friends with Edward:
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say the friend.
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[We can also define relations that exist procedurally.]
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Helpfulness relates a person (called the helper) to a person (called the helpee) when the helpee is blind and the helper is not blind.
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The verb to be helpful to means the helpfulness relation.
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To demonstrate using a procedural relation:
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repeat with the helper running through people that are helpful to Edward:
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say the helper.
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[ Interface to the text adventure harness to allow the above code to be run. ]
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Tutorial room is a room.
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"A rather strange room full of buttons. Push them to run the exercises, or turn on the robot to run them all."
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A button is a kind of thing. A button is fixed in place.
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The red button is a button in tutorial room.
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Instead of pushing the red button, do the thing everyone does with their first program.
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The green button is a button in tutorial room.
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Instead of pushing the green button, demonstrate calling a phrase with two parameters.
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The blue button is a button in tutorial room.
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Instead of pushing the blue button, show how to use list types.
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The cyan button is a button in tutorial room.
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Instead of pushing the cyan button, say the sum of all numbers up to 5.
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The purple button is a button in tutorial room.
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Instead of pushing the purple button, demonstrate a higher order function.
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The black button is a button in tutorial room.
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Instead of pushing the black button, demonstrate defining a higher order function.
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The white button is a button in tutorial room.
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Instead of pushing the white button, demonstrate invoking a rulebook.
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The puce button is a button in tutorial room.
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Instead of pushing the puce button, demonstrate looking something up with a relation.
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The orange button is a button in tutorial room.
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Instead of pushing the orange button, demonstrate using a procedural relation.
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The robot is an object in tutorial room.
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Instead of switching on the robot:
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say "The robot begins to frantically flail its arms about.";
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repeat with button running through buttons in the tutorial room:
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say "The robot randomly hits [the button].";
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try pushing button.
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```
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##Ready For More?
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* [Inform 7](http://www.inform7.com/)
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