refactor: add chapter content

License: MIT
Signed-off-by: Vaibhav Saini <[email protected]>

Author: vasa-develop

.prettierrc

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+{
+  "tabWidth": 2,
+  "useTabs": false,
+  "singleQuote": true
+}

1/contract_structure.md

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-# Contract Structure
+# Structure of a Contract
 
-TODO: Add Lesson for Contract Structure
+Vyper contracts are contained within files. Each file contains exactly
+one contract.
+
+This section provides a quick overview of the types of data present
+within a contract, with links to other sections where you can obtain
+more details.
+
+## Version Pragma
+
+Vyper supports a version pragma to ensure that a contract is only
+compiled by the intended compiler version, or range of versions. Version
+strings use [NPM](https://docs.npmjs.com/misc/semver) style syntax.
+
+```python
+# @version ^0.2.0
+```
+
+In the above example, the contract only compiles with Vyper versions
+`0.2.x`.
+
+## State Variables
+
+State variables are values which are permanently stored in contract
+storage. They are declared outside of the body of any functions, and
+initially contain the default value\<types-initial\> for their type.
+
+```python
+storedData: int128
+```
+
+State variables are accessed via the self\<constants-self\> object.
+
+```python
+self.storedData = 123
+```
+
+See the documentation on Types \<types\> or [Scoping and
+Declarations](scoping) for more information.
+
+## Functions
+
+Functions are executable units of code within a contract.
+
+```python
+@external
+def bid():
+    ...
+```
+
+Functions may be called internally or externally depending on their
+visibility \<function-visibility\>. Functions may accept input arguments
+and return variables in order to pass values between them.
+
+See the Functions \<control-structures-functions\> documentation for
+more information.
+
+## Events
+
+Events provide an interface for the EVM's logging facilities. Events may
+be logged with specially indexed data structures that allow clients,
+including light clients, to efficiently search for them.
+
+```python
+event Payment:
+    amount: int128
+    sender: indexed(address)
+
+total_paid: int128
+
+@external
+@payable
+def pay():
+    self.total_paid += msg.value
+    log Payment(msg.value, msg.sender)
+```
+
+See the Event \<event-logging\> documentation for more information.
+
+## Interfaces
+
+An interface is a set of function definitions used to enable calls
+between smart contracts. A contract interface defines all of that
+contract's externally available functions. By importing the interface,
+your contract now knows how to call these functions in other contracts.
+
+Interfaces can be added to contracts either through inline definition,
+or by importing them from a seperate file.
+
+```python
+interface FooBar:
+    def calculate() -> uint256: view
+    def test1(): nonpayable
+```
+
+```python
+from foo import FooBar
+```
+
+Once defined, an interface can then be used to make external calls to a
+given address:
+
+```python
+@external
+def test(some_address: address):
+    FooBar(some_address).calculate()
+```
+
+See the Interfaces \<interfaces\> documentation for more information.
+
+## Structs
+
+A struct is custom defined type that can allows you to group several
+variables together:
+
+```python
+struct MyStruct:
+    value1: int128
+    value2: decimal
+```
+
+See the Structs \<types-struct\> documentation for more information.
 
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 #### ** Template **
 
-[embedded-code](../assets/1/1.1-template-code.vy ":include :type=code embed-template")
+[embedded-code](../assets/1/1.1-template-code.vy ':include :type=code embed-template')
 
 #### ** Solution **
 
-[embedded-code-final](../assets/1/1.1-finished-code.vy ":include :type=code embed-final")
+[embedded-code-final](../assets/1/1.1-finished-code.vy ':include :type=code embed-final')
 
 #### ** Previous Chapter Solution **
 
-[embedded-code-previous](../assets/1/1.0-finished-code.vy ":include :type=code embed-previous")
+[embedded-code-previous](../assets/1/1.0-finished-code.vy ':include :type=code embed-previous')
 
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