// A Small Compiler for the WHILE Language with Arrays

// (it does not use a parser and lexer)

// the new parts are

//    - declaring an array

//    - references an array cell

//    - assigning an array cell

// 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 AssignA(s: String, a1: AExp, a2: AExp) extends Stmt

case class Write(s: String) extends Stmt

case class Array(s: String, n: Int) 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

case class Ref(s: String, a1: 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 an init method, as well as methods for read and write)

val beginning = """

.class public XXX.XXX

.super java/lang/Object

.method public <init>()V

   aload_0

   invokenonvirtual java/lang/Object/<init>()V

   return

.end method

.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

import scala.language.implicitConversions

import scala.language.reflectiveCalls

implicit def sring_inters(sc: StringContext) = new {

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

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

}

// environments 

type Env = Map[String, String]

// 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)}"

  case Aop("+", a1, a2) => 

    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ i"iadd"

  case Aop("-", a1, a2) => 

    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ i"isub"

  case Aop("*", a1, a2) => 

    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ i"imul"

  case Ref(s, a1) => 

    i"aload ${env(s)}" ++ compile_aexp(a1, env) ++ i"iaload"  

}

// boolean expression compilation

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 = if (env.isDefinedAt(x)) env(x) else 

                    env.keys.size.toString

    (compile_aexp(a, env) ++ i"istore $index", 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)

    (compile_bexp(b, env, if_else) ++

     instrs1 ++

     i"goto $if_end" ++

     l"$if_else" ++

     instrs2 ++

     l"$if_end", env2)

  }

  case While(b, bl) => {

    val loop_begin = Fresh("Loop_begin")

    val loop_end = Fresh("Loop_end")

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

    (l"$loop_begin" ++

     compile_bexp(b, env, loop_end) ++

     instrs1 ++

     i"goto $loop_begin" ++

     l"$loop_end", env1)

  }

  case Write(x) => 

    (i"iload ${env(x)}" ++ 

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

  case Array(s, n) => {

    val index = if (env.isDefinedAt(s)) throw new Exception("Array already defined") else 

                    env.keys.size.toString

    (i"ldc $n" ++

     i"newarray int" ++

     i"astore $index", env + (s -> index))

  } 

  case AssignA(s, a1, a2) => {

    val index = if (env.isDefinedAt(s)) env(s) else 

                    throw new Exception("Array not yet defined")

    (i"aload $index" ++

     compile_aexp(a1, env) ++

     compile_aexp(a2, env) ++

     i"iastore", 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.mkString ++ ending).replaceAllLiterally("XXX", class_name)

}

// main compiler functions

import scala.util._

import scala.sys.process._

import scala.io

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

  val output = compile(bl, class_name)

  scala.tools.nsc.io.File(s"${class_name}.j").writeAll(output)

}

def compile_all(bl: Block, class_name: String) : Unit = {

  compile_tofile(bl, class_name)

  println("compiled ")

  (s"java -jar jvm/jasmin-2.4/jasmin.jar ${class_name}.j").!!

  println("assembled ")

}

def time_needed[T](i: Int, code: => T) = {

  val start = System.nanoTime()

  for (j <- 1 to i) code

  val end = System.nanoTime()

  (end - start)/(i * 1.0e9)

}

def compile_run(bl: Block, class_name: String) : Unit = {

  println("Start compilation")

  compile_all(bl, class_name)

  println("Start running")

  println("Time: " + time_needed(1, (s"java ${class_name}/${class_name}").!))

}

// a simple test case

val arr_test = 

  List(Array("a", 10),                 // a[10]

       Array("b", 2),                  // b[2]

       AssignA("a", Num(0), Num(10)),  // a[0] := 10

       Assign("x", Ref("a", Num(0))),  // x := a[0]

       Write("x"),                     // write x

       AssignA("b", Num(1), Num(5)),   // b[1] := 5

       Assign("x", Ref("b", Num(1))),  // x := b[1]

       Write("x"))                     // write x

compile_run(arr_test, "a")