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+---
+name: niva
+filename: main.niva
+contributors:
+    - ["gavr", "https://github.com/gavr123456789"]
+---
+
+## Intro
+Niva is a simple language that takes a lot of inspiration from Smalltalk.  
+But leaning towards the functional side and static typed.
+Everything is still an object, but instead of classes, interfaces, inheritance, and abstract classes,  
+we have tagged unions, which is the only way to achieve polymorphism.
+
+
+For example, everything except the declaration is sending messages to objects.  
+`1 + 2` is not a + operator, but a `... + Int` message for `Int` object.
+(there are no extra costs for that)   
+
+C-like: `1.inc()`  
+Niva: `1 inc`  
+
+In essence, niva is highly minimalistic, like its ancestor Smalltalk.  
+It introduces types, unions, and associated methods. 
+There are no functions.
+
+Install:
+```bash
+git clone https://github.com/gavr123456789/Niva.git
+cd Niva
+./gradlew buildJvmNiva
+# LSP here https://github.com/gavr123456789/niva-vscode-bundle
+```
+
+## The Basics
+
+#### Variable
+Variables are immutable by default.
+There is no special keyword for declaring a variable.
+
+```Scala
+// this is a comment
+int = 1 
+str = "qwf"
+boolean = true 
+char = 'a'
+float = 3.14f
+double = 3.14
+mutltiLineStr = """
+qwf ars zxc \n \t "qwf"
+"""
+explicit_type::Int = 5
+
+
+list = {1 2 3}  
+set = #(1 2 3) 
+map = #{1 'a' 2 'b'} 
+
+// declare a mutable variable
+mut x = 5
+x <- 6 // mutate
+```
+
+#### Messages
+```Scala
+// hello world is a one liner
+"Hello world" echo // echo is a message for String obj
+
+
+// There are 3 types of messages
+1 inc // 2         unary 
+1 + 2 // 3         binary
+"abc" at: 0 // 'a' keyword
+
+
+// they can be chained
+1 inc inc inc dec // 3
+1 + 1 + 2 - 3 // 1
+1 to: 3 do: [it echo] // 1 2 3
+// the last one here to:do: is a single message
+// to chain 2 keyword messages you need to wrap it in parentheses
+("123456" drop: 1) dropLast: 2 // "234" 
+the comma `,` is syntactic sugar for the same effect
+"123456" drop: 1, dropLast: 2 // "234" 
+
+// you can mix them
+1 inc + 3 dec - "abc" count // 2 + 2 - 3 -> 1
+"123" + "456" drop: 1 + 1   // "123456" drop: 2 -> "3456"
+
+// everything except type and message declarations are message sends in niva
+// for example `if` is a message for Boolean object that takes a lambda
+1 > 2 ifTrue: ["wow" echo]
+// expression
+base = 1 > 2 ifTrue: ["heh"] ifFalse: ["qwf"]
+// same for while
+mut q = 0
+[q > 10] whileTrue: [q <- q inc]
+// all of this is zero cost because of inlining at compile time
+```
+
+#### Type
+New lines are not significant in niva  
+Type declarations look like keyword messages consisting of fields and types
+```Scala
+type Square side: Int
+
+type Person
+  name: String
+  age: Int
+```
+
+#### Create instance
+Creating an object is the same keyword message as when declaring it, but with values in place of types.
+```Scala
+square = Square side: 42
+alice = Person name: "Alice" age: 24
+
+// destruct fields by names
+{age name} = alice
+```
+
+#### Access fields
+Getting fields is the same as sending a unary message with its name to the object 
+```Scala
+// get age, add 1 and print it
+alice age inc echo // 25
+```
+
+#### Method for type:  
+Everything is an object, just like in Smalltalk, so everything can have a method declared.   
+Here, we add a `double` method to `Int` and then use it inside the `perimeter` method of `Square`.  
+
+```Scala
+Int double = this + this
+Square perimeter = side double
+
+square = Square side: 42
+square perimeter // call
+
+
+// explicit return type
+Int double2 -> Int = this * 2
+
+// with body
+Int double3 -> Int = [
+    result = this * 2
+    ^ result // ^ is return
+]
+```
+
+
+#### Keyword message declaration
+```Scala
+type Range from: Int to: Int
+// keyword message with one arg `to`
+Int to::Int = Range from: this to: to
+
+1 to: 2 // Range
+```
+#### Type constructor
+A type constructor functions as a message for the type itself rather than to a specific instance.
+```Scala
+constructor Float pi = 3.14
+x = Float pi // 3.14
+```
+
+It can be useful for initializing fields with default values.
+```Scala
+type Point x: Int y: Int
+constructor Point atStart = Point x: 0 y: 0
+
+p1 = Point x: 0 y: 0
+p2 = Point atStart
+// constructor is just a usual message, so it can have params
+constructor Point y::Int = Point x: 0 y: y
+p3 = Point y: 20 // x: 0 y: 20
+```
+
+
+#### Conditions
+If, like everything else, is the usual sending of a message to a Boolean object.  
+It takes one or two lambda arguments. 
+```Scala
+false ifTrue: ["yay" echo]
+1 < 2 ifTrue: ["yay" echo]
+1 > 2 ifTrue: ["yay" echo] ifFalse: ["oh no" echo]
+
+// `ifTrue:ifFalse:` message can be used as expression
+str = 42 % 2 == 0 
+    ifTrue: ["even"]
+    ifFalse: ["odd"]
+// str == "even"
+```
+
+#### Cycles
+There is no special syntax for cycles.  
+It's just keyword messages that take codeblocks as parameters.  
+(it's zero cost thanks for inlining)
+```Scala
+{1 2 3} forEach: [ it echo ] // 1 2 3
+1..10 forEach: [ it echo ]
+
+mut c = 10
+[c > 0] whileTrue: [ c <- c dec ]
+
+c <- 3 // reset c
+[c > 0] whileTrue: [ 
+    c <- c dec 
+    c echo // 3 2 1
+]
+```
+`whileTrue:` is a message for lambda object of the type: 
+`[ -> Boolean] whileTrue::[ -> Unit]`
+
+#### Matching
+there is special syntax for matching, since niva heavily utilize tagged unions
+```Scala
+x = "Alice"
+// matching on x
+| x
+| "Bob" => "Hi Bob!"
+| "Alice" => "Hi Alice!"
+|=> "Hi guest"
+
+
+// It can be used as expression as well
+y = | "b"
+    | "a" => 1
+    | "b" => 2
+    |=> 0
+y echo // 2
+```
+
+#### Tagged unions
+
+```Scala
+union Color = Red | Blue | Green
+
+// branches can have fields
+union Shape =
+    | Rectangle width: Int height: Int
+    | Circle    radius: Double
+    
+constructor Double pi = 3.14
+Double square = this * this
+
+// match on this(Shape)
+Shape getArea -> Double = 
+    | this 
+    | Rectangle => width * height, toDouble
+    | Circle => Double pi * radius square
+    
+// There is exhaustiveness checking, so when you add a new branch 
+// all the matches will become errors until all cases processed
+
+Shape getArea -> Double = | this 
+    | Rectangle => width * height, toDouble 
+// ERROR: Not all possible variants have been checked (Circle)
+```
+
+#### Collections 
+```Scala
+// commas are optional
+list = {1 2 3} 
+map = #{'a' 1 'b' 2}
+map2 = #{'a' 1, 'b' 2, 'c' 3}
+set = #(1 2 3)
+
+// common collection operations
+{1 2 3 4 5} 
+  map: [it inc], 
+  filter: [it % 2 == 0],
+  forEach: [it echo] // 2 4 6
+
+// iteration on map
+map forEach: [key, value -> 
+  key echo 
+  value echo
+]
+```
+
+#### Nullability
+By default, variables cannot be assigned a null value.  
+To allow this, nullable types are used, indicated by a question mark at the end of the type.  
+You may already be familiar with this concept from TypeScript, Kotlin, or Swift.
+```Scala
+x::Int? = null
+q = x unpackOrPANIC
+
+// do something if it's not null
+x unpack: [it echo]
+
+// same but provide a backup value
+w = x unpack: [it inc] or: -1
+
+// just unpack or backup value
+e = x unpackOrValue: -1
+```
+
+#### Handling the error
+```Scala
+// exit the program with stack trace
+x = file read orPANIC
+x = file read orValue: "no file"
+```
+Errors work like effects, look for more in [Error handling](https://gavr123456789.github.io/niva-site/error-handling.html)
+
+## Misc
+
+#### Local arg names
+```Scala
+Int from: x::Int to: y::Int = this + x + y
+```
+
+#### Syntax sugar for this
+```Scala
+Person foo = [
+    .bar
+    this bar // same thing
+]
+```
+
+#### Compile time reflection
+You can get string representation of any argument from a call site.
+```Scala
+Int bar::Int baz::String = [
+    // getting string representation from call side
+    a = Compiler getName: 0
+    b = Compiler getName: 1
+    c = Compiler getName: 2
+    a echo // 1 + 1
+    b echo // variable
+    c echo // "str"
+]
+
+variable = 42
+// call side
+1 + 1 
+    bar: variable 
+    baz: "str"
+```
+
+Links:
+- [Site](https://gavr123456789.github.io/niva-site/reference.html)
+- [GitHub](https://github.com/gavr123456789/Niva)
+- [LSP](https://github.com/gavr123456789/vaLSe)
+- [VSC plugin](https://github.com/gavr123456789/niva-vscode-bundle)