Bytc - bytc your code

Purely functional byte code and class file generator written in Scala3

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Designs

• The core class Code and ClassFile.Operation are purely composable, which implement Monoid.
• No side effect until we have to write file (IO).
• Computation description and interpreter implementation properly seperated (Free monad is not necessary with Scala's implicits).

Usage

Useful codes

• Pass serves as the empty code
• Load Intelligently load various kinds of data types
• Store Intelligently store various kinds of data types
• Return Intelligently return with return type
• Inspect Inspect intermediate code state
• PrintCode Print codes
• NewCode Customize code as you like
• New new instances
• InvokeVirtual invoke methods
• ...

Useful classfile operations

• Define defines a new class
• Main adds main method
• Method adds method
• Constructor adds constructor
• DefaultConstructor adds default constructor
• ...

Examples

Necessary imports

import bytc.*
import bytc.given
import Type.*

Hello world

@main def main: Unit = 
  import Code.*

  import ClassFile.Operation.*
  val `class` = 
    Define("HelloWorld")
      << DefaultConstructor
      << Main(helloWorld)

  `class`.create() match
    case Left(err) => sys.error(err.msg)
    case Right(cf) => cf.writeToFile("HelloWorld.class")
end main

def helloWorld: Code = {
  import Code.*
  
  Comment("Hello world example")
    << GetStatic("java.lang.System", "out", "Ljava/io/PrintStream;")
    << Load("Hello world!")
    << InvokeVirtual("java.io.PrintStream", "println", "(Ljava/lang/String;)V")
    << Return
}

Factorial

def fact: Code = {
  import Code.*
  
  val label = Tool.getFreshLabel()

  Comment("Define fact(n: Int): Int") 
    << Load(Var(1)) 
    << Load(1)
    << If_ICmpGt(label) 
    << Load(1) 
    << Return
    << Label(label)
    << Load(Var(1)) 
    << Load(Var(0))
    << Load(Var(1)) 
    << Load(1) 
    << ISUB 
    << InvokeVirtual("HelloWorld", "fact", "(I)I")
    << IMUL 
    << Return
}