diff -r 2b6e23985982 -r 89f9c68fc417 progs/while-arrays/compile_arrays2.sc
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/while-arrays/compile_arrays2.sc	Fri Dec 04 14:48:40 2020 +0000
@@ -0,0 +1,256 @@
+// A Small Compiler for the WHILE Language
+//
+// - this compiler contains support for "static" integer 
+//   arrays (they are mutable but cannot be re-sized)
+//
+// Call with 
+//
+// amm compile_arrays.sc
+  
+
+// the abstract syntax trees for WHILE
+
+abstract class Stmt
+abstract class AExp
+abstract class BExp 
+type Block = List[Stmt]
+
+// statements
+case object Skip extends Stmt
+case class ArrayDef(s: String, n: Int) extends Stmt            // array definition
+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             // var := exp
+case class AssignA(s: String, a1: AExp, a2: AExp) extends Stmt // arr[exp1] := exp2
+case class Write(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
+case class Ref(s: String, a: 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 main method and a method for writing out an integer
+//
+// - the stack and locals are hard-coded
+//
+
+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/print(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
+"""
+
+
+
+// for generating new labels
+var counter = -1
+
+def Fresh(x: String) = {
+  counter += 1
+  x ++ "_" ++ counter.toString()
+}
+
+// environments for variables and indices
+type Env = Map[String, Int]
+
+// convenient string interpolations 
+// for generating instructions and labels
+
+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"
+}
+
+def compile_num(i: Int) = 
+  if (0 <= i && i <= 5) i"iconst_$i" else 
+  if (-128 <= i && i <= 127) i"bipush $i" else i"ldc $i"
+
+def compile_aload(i: Int) = 
+  if (0 <= i && i <= 3) i"aload_$i" else i"aload $i"
+
+def compile_astore(i: Int) = 
+  if (0 <= i && i <= 3) i"astore_$i" else i"astore $i"
+
+def compile_iload(i: Int) = 
+  if (0 <= i && i <= 3) i"iload_$i" else i"iload $i"
+
+def compile_istore(i: Int) = 
+  if (0 <= i && i <= 3) i"istore_$i" else i"istore $i"
+
+
+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) => compile_num(i)
+  case Var(s) => compile_iload(env(s))
+  case Aop(op, a1, a2) => 
+    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ compile_op(op)
+  case Ref(s, a) =>
+    compile_aload(env(s)) ++ compile_aexp(a, 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 = env.getOrElse(x, env.keys.size)
+    (compile_aexp(a, env) ++ compile_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) => 
+    (compile_iload(env(x)) ++ 
+     i"invokestatic XXX/XXX/write(I)V", env)
+  case ArrayDef(s: String, n: Int) => {
+    val index = if (env.isDefinedAt(s)) throw new Exception("array def error") else 
+                    env.keys.size
+    (compile_num(n) ++
+     i"newarray int" ++
+     compile_astore(index), env + (s -> index))
+  }
+  case AssignA(s, a1, a2) => {
+    val index = if (env.isDefinedAt(s)) env(s) else 
+                    throw new Exception("array not defined")
+    (compile_aload(env(s)) ++
+     compile_aexp(a1, env) ++
+     compile_aexp(a2, env) ++
+     i"iastore", env)
+  } 
+}
+
+// compile a block (i.e. list of statements)
+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 compile function for blocks (adds headers and proper JVM names)
+def compile(bl: Block, class_name: String) : String = {
+  val instructions = compile_block(bl, Map())._1
+  (beginning ++ instructions ++ ending).replace("XXX", class_name)
+}
+
+
+
+// contrived example involving arrays
+val array_test = 
+  List(ArrayDef("a", 10),               // array a[10]
+       ArrayDef("b", 2),                // array b[2]
+       AssignA("a", Num(0), Num(10)),   // a[0] := 10
+       Assign("x", Ref("a", Num(0))),   // x := a[0]
+       Write("x"),            
+       AssignA("b", Num(1), Num(5)),    // b[1] := 5
+       Assign("x", Ref("b", Num(1))),   // x := b[1] 
+       Write("x"))                     
+
+
+// prints out the JVM-assembly instructions for fib above
+//
+//    println(compile(array_test, "arr"))
+//
+// can be assembled by hand with 
+//
+//    java -jar jasmin.jar arr.j
+//
+// and run with
+//
+//    java arr/arr
+
+// automating the above
+import ammonite.ops._
+
+def compile_to_file(bl: Block, class_name: String) : Unit = 
+  write.over(pwd / s"$class_name.j", compile(bl, class_name))  
+
+def compile_and_run(bl: Block, class_name: String) : Unit = {
+  println(s"Start of compilation")
+  compile_to_file(bl, class_name)
+  println(s"generated $class_name.j file")
+  os.proc("java", "-jar", "jasmin.jar", s"$class_name.j").call()
+  println(s"generated $class_name.class file ")
+  //println(os.proc("java", s"${class_name}/${class_name}").call().out.text())
+  os.proc("java", s"${class_name}/${class_name}").call(stdout = os.Inherit)
+  println(s"done.")
+}
+
+
+   
+@main def main() = {
+  compile_and_run(array_test, "arr")
+}
+
+