yukitai / yak

a powerful compiler for advanced scratch developers

the Yak Programming Language

warning: this project is still on working

Yak projects can be compiled into a Scratch(.sb3) file.

Docs

1. Compiler - RIP

2. Yak Guide

   Yak's syntax is like Python, but it only allows definitions in the top-level scope. Here is an example of a yak source file:

   def Fact(n) -> num:
       if n < 2:
           return 1
       return n * Fact(n - 1)

   It looks like Python, isn't it? Okay, let's get Yaking.

   Identifiers

   Identifiers can include letters, the underscore(_) and numbers and identifiers cannot start with a number.

   Yak has some keywords that cannot be used as an identifier. Here are these keywords:

   def struct use for in while if elif else return unit  num str bool list nil _
   

   Yak has another identifier that can include any charactors you want, they start with a r# and end with a #.

   Identifier can be connect into a new identifier using ::. Here are some examples:

   abc r#+# r#def# abc::ghi::r#return#
   

   Fucntions

   Functions start with a def keyword, an identifier, an optional generics list, an argument list, an optional return type, a colon(:) and a function body. A empty body must include a ....

   warning: a function with generic types or struct types cannot be compiled into a vaild Scratch project

   def Func1():
       ...
    
   def Func2<T, U>(a: T, b: num, c, d: U) -> num:
       ...

   Yak's compiler will try to infer the type of identifiers with no type hint and produce an error if the compiler fails to infer.

   Structs

   Structs start with a struct keyword, an identifier, an optional generics list, a colon(:) and a struct body. Empty structs are not allowed.

   struct Pair<T, U>:
       _0: T
       _1: U

   Call a function with generics

   If you want to call a function with generics, you need to use ::<> after the function name to specify the function's type. Here's an Example:

   def Eq<T>(lhs: T, rhs: T) -> bool:
       return lhs == rhs
   
   def Test(x: num, y: num) -> bool:
       return Eq::<num>(x, y)

   Globals

   An identifier starts with a uppercase letter will be exported to the global scope.

3. How does yak work?

   warning: this session is still on working

   First, yak's compiler spilts the source file into tokens and parses them into an AST(Abstract Syntax Tree) object. Second, scan the AST and bind all identifiers to its definition. Third, infer the type of any identifiers and expressions. Fourth, translate the AST into a lower Scratch IR and emits a vaild json of some Scratch blocks.

   An example of lower Scratch IR translation:

   def Fact(n):
       if n < 2:
           return 1
       return n * Fact(n - 1)

   the lower Scratch IR: