# Basics

## Structure of Sircle Source

A Sircle source file consists a sequence of global bindings. For example:

Example

  1 2 3 4 5 6 7 8 9 10 11 type Foo = { "x": Double, "y": Double } def point: Foo = { "x" -> 1.0, "y" -> 2.0 } def printFoo = p: Foo => { print "(" print (p."x") print ", " print (p."y") println ")\n" } 

The above source example binds three names in the top level: Foo, point, and printFoo. There are two types of global bindings:

• Type binding. Example: type Foo = { "x": Double, "y": Double }. It is similar to type aliasing in other languages.
• Value binding. Example: def point: Foo = ... and def printFoo = .... It binds a value to a name in the top level.

## Basic Datatypes

### Primitive Types

Type C++ Type Scala Type Haksell Type
Int int Int Int
Double double Double Double
String std::string String Data.Text
Boolean bool Boolean Boolean
Unit Unit ()
Any Unit forall a. a

Any value of Any type can be assumed a value of type Any.

### List Type

List in Sircle is similar to list in Python, which can contain values of different types. Therefore, List type is not parameterized, and any List value has the same List type.

We can construct a list in Sircle by using list lexemes. For instance,

 1 def xs = [1, "2", False] 

We can access list elements using its index.

 1 2 xs.1 // => "2" 

The cons built-in function can be used to prepend a value to a list.

 1 2 cons 1 [2, 3] // => [1, 2, 3] 

Additionally, we can concat two lists simply using the + operator.

 1 2 [1, 2, 3] + ["4", "5", "6"] // => [1, 2, 3, "4", "5", "6"] 

Some library functions are defined in Sircle Prelude to manipulate list values.

 1 2 3 4 5 6 7 8 map show [1, 2, 3] // => ["1", "2", "3"] foldl (x => y => x * y) 1 [1, 2, 3] // => 6 zipWith (x => y => show x + show y) [1, 2, 3] [True, False, True] // => ["1True", "2False", "3True"]