// A Small Compiler for the WHILE Language

// (it does not use a parser nor lexer)

//

// call with 

//

//   amm compile.sc test

//   amm compile.sc test2

//

// test2 includes a run of the JVM instructions. This

// requires that jasmin.jar is present in the same 

// directory.

// the abstract syntax trees

abstract class Stmt

abstract class AExp

abstract class BExp 

type Block = List[Stmt]

// statements

case object Skip extends Stmt

case class If(a: BExp, bl1: Block, bl2: Block) extends Stmt

case class While(b: BExp, bl: Block) extends Stmt

case class Assign(s: String, a: AExp) extends Stmt

case class Write(s: String) extends Stmt

case class Read(s: String) extends Stmt

// arithmetic expressions

case class Var(s: String) extends AExp

case class Num(i: Int) extends AExp

case class Aop(o: String, a1: AExp, a2: AExp) extends AExp

// boolean expressions

case object True extends BExp

case object False extends BExp

case class Bop(o: String, a1: AExp, a2: AExp) extends BExp

// compiler headers needed for the JVM

// (contains a method for write)

val beginning = """

.class public XXX.XXX

.super java/lang/Object

.method public static write(I)V 

    .limit locals 1 

    .limit stack 2 

    getstatic java/lang/System/out Ljava/io/PrintStream; 

    iload 0

    invokevirtual java/io/PrintStream/println(I)V 

    return 

.end method

.method public static main([Ljava/lang/String;)V

   .limit locals 200

   .limit stack 200

; COMPILED CODE STARTS

"""

val ending = """

; COMPILED CODE ENDS

   return

.end method

"""

// Compiler functions

// for generating new labels

var counter = -1

def Fresh(x: String) = {

  counter += 1

  x ++ "_" ++ counter.toString()

}

// convenient string interpolations 

// for instructions and labels

extension (sc: StringContext) {

    def i(args: Any*): String = "   " ++ sc.s(args:_*) ++ "\n"

}

// this allows us to write things like

// i"iadd" and l"Label"

// environments 

type Env = Map[String, Int]

def compile_op(op: String) = op match {

  case "+" => i"iadd"

  case "-" => i"isub"

  case "*" => i"imul"

}

// arithmetic expression compilation

def compile_aexp(a: AExp, env : Env) : String = a match {

  case Num(i) => i"ldc $i"

  case Var(s) => i"iload ${env(s)} \t\t; $s"

  case Aop(op, a1, a2) => 

    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ compile_op(op)

}

// boolean expression compilation

//  - the jump-label is for where to jump if the condition is not true

def compile_bexp(b: BExp, env : Env, jmp: String) : String = b match {

  case True => ""

  case False => i"goto $jmp"

  case Bop("==", a1, a2) => 

    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ i"if_icmpne $jmp"

  case Bop("!=", a1, a2) => 

    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ i"if_icmpeq $jmp"

  case Bop("<", a1, a2) => 

    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ i"if_icmpge $jmp"

}

// statement compilation

def compile_stmt(s: Stmt, env: Env) : (String, Env) = s match {

  case Skip => ("", env)

  case Assign(x, a) => {

    val index = env.getOrElse(x, env.keys.size)

    (compile_aexp(a, env) ++ i"istore $index \t\t; $x", env + (x -> index))

  } 

  case If(b, bl1, bl2) => {

    val if_else = Fresh("If_else")

    val if_end = Fresh("If_end")

    val (instrs1, env1) = compile_block(bl1, env)

    val (instrs2, env2) = compile_block(bl2, env1)

    (s"""|${compile_bexp(b, env, if_else)}

         |${instrs1}

         |${i"goto $if_end"}

         |${l"$if_else"}

         |${instrs2}

         |${l"$if_end"}""".stripMargin, env2)

  }

  case While(b, bl) => {

    val loop_begin = Fresh("Loop_begin")

    val loop_end = Fresh("Loop_end")

    val (instrs1, env1) = compile_block(bl, env)

    (s"""|${l"$loop_begin"}

         |${compile_bexp(b, env, loop_end)}

         |$instrs1

         |${i"goto $loop_begin"}

         |${l"$loop_end"}""".stripMargin, env1)

  }

  case Write(x) => 

    (i"iload ${env(x)} \t\t; $x" ++ 

     i"invokestatic XXX/XXX/write(I)V", env)

}

// compilation of a block (i.e. list of instructions)

def compile_block(bl: Block, env: Env) : (String, Env) = bl match {

  case Nil => ("", env)

  case s::bl => {

    val (instrs1, env1) = compile_stmt(s, env)

    val (instrs2, env2) = compile_block(bl, env1)

    (instrs1 ++ instrs2, env2)

  }

}

// main compilation function for blocks

def compile(bl: Block, class_name: String) : String = {

  val instructions = compile_block(bl, Map.empty)._1

  (beginning ++ instructions ++ ending).replace("XXX", class_name)

}

// Fibonacci numbers as a bare-bone test-case

val fib_test = 

  List(Assign("n", Num(9)),            //  n := 9;                     

       Assign("minus1",Num(0)),         //  minus1 := 0;

       Assign("minus2",Num(1)),         //  minus2 := 1;

       Assign("temp",Num(0)),           //  temp := 0;

       While(Bop("<",Num(0),Var("n")),  //  while 0 < n do  {

          List(Assign("temp",Var("minus2")), //  temp := minus2;

               Assign("minus2",Aop("+",Var("minus1"),Var("minus2"))), 

                                        //  minus2 := minus1 + minus2;

               Assign("minus1",Var("temp")), //  minus1 := temp;

               Assign("n",Aop("-",Var("n"),Num(1))))), //  n := n - 1 };

       Write("minus1"))                 //  write minus1

// prints out the JVM instructions

@main

def test() = 

  println(compile(fib_test, "fib"))

// compiling and running .j-files

//

// JVM files can be assembled with 

//

//    java -jar jasmin.jar fib.j

//

// and started with

//

//    java fib/fib

def run(bl: Block, class_name: String) = {

    val code = compile(bl, class_name)

    os.write.over(os.pwd / s"$class_name.j", code)

    os.proc("java", "-jar", "jasmin.jar", s"$class_name.j").call()

    os.proc("java", s"$class_name/$class_name").call(stdout = os.Inherit, stdin = os.Inherit)

    ()

}

@main

def test2() =

  run(fib_test, "fib")

/* Jasmin code for reading an integer

.method public static read()I 

    .limit locals 10 

    .limit stack 10

    ldc 0 

    istore 1  ; this will hold our final integer 

Label1: 

    getstatic java/lang/System/in Ljava/io/InputStream; 

    invokevirtual java/io/InputStream/read()I 

    istore 2 

    iload 2 

    ldc 10   ; the newline delimiter 

    isub 

    ifeq Label2 

    iload 2 

    ldc 32   ; the space delimiter 

    isub 

    ifeq Label2

    iload 2 

    ldc 48   ; we have our digit in ASCII, have to subtract it from 48 

    isub 

    ldc 10 

    iload 1 

    imul 

    iadd 

    istore 1 

    goto Label1 

Label2: 

    ; when we come here we have our integer computed in local variable 1 

    iload 1 

    ireturn 

.end method

*/