diff -r 698ed1c96cd0 -r 4ce07c4abdb4 progs/fun-bare.scala
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/fun-bare.scala	Fri Apr 10 18:02:04 2015 +0100
@@ -0,0 +1,174 @@
+// A Small Compiler for a simple functional language
+
+// Abstract syntax trees
+abstract class Exp
+abstract class BExp 
+abstract class Decl
+
+// function declarations
+case class Def(name: String, args: List[String], body: Exp) extends Decl
+case class Main(e: Exp) extends Decl
+
+// expressions
+case class Call(name: String, args: List[Exp]) extends Exp
+case class If(a: BExp, e1: Exp, e2: Exp) extends Exp
+case class Write(e: Exp) extends Exp
+case class Var(s: String) extends Exp
+case class Num(i: Int) extends Exp
+case class Aop(o: String, a1: Exp, a2: Exp) extends Exp
+case class Sequ(e1: Exp, e2: Exp) extends Exp
+
+// boolean expressions
+case class Bop(o: String, a1: Exp, a2: Exp) extends BExp
+
+// calculating the maximal needed stack size
+def max_stack_exp(e: Exp): Int = e match {
+  case Call(_, args) => args.map(max_stack_exp).sum
+  case If(a, e1, e2) => max_stack_bexp(a) + (List(max_stack_exp(e1), max_stack_exp(e2)).max)
+  case Write(e) => max_stack_exp(e) + 1
+  case Var(_) => 1
+  case Num(_) => 1
+  case Aop(_, a1, a2) => max_stack_exp(a1) + max_stack_exp(a2)
+  case Sequ(e1, e2) => List(max_stack_exp(e1), max_stack_exp(e2)).max
+}
+def max_stack_bexp(e: BExp): Int = e match {
+  case Bop(_, a1, a2) => max_stack_exp(a1) + max_stack_exp(a2)
+}
+
+// compiler - built-in functions 
+// copied from http://www.ceng.metu.edu.tr/courses/ceng444/link/jvm-cpm.html
+//
+
+val library = """
+.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 5 
+        .limit stack 5 
+        iload 0 
+        getstatic java/lang/System/out Ljava/io/PrintStream; 
+        swap 
+        invokevirtual java/io/PrintStream/println(I)V 
+        return 
+.end method
+
+"""
+
+// for generating new labels
+var counter = -1
+
+def Fresh(x: String) = {
+  counter += 1
+  x ++ "_" ++ counter.toString()
+}
+
+
+type Env = Map[String, Int]
+type Instrs = List[String]
+
+// compile expressions
+def compile_exp(a: Exp, env : Env) : Instrs = a match {
+  case Num(i) => List("ldc " + i.toString + "\n")
+  case Var(s) => List("iload " + env(s).toString + "\n")
+  case Aop("+", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ List("iadd\n")
+  case Aop("-", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ List("isub\n")
+  case Aop("*", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ List("imul\n")
+  case Aop("/", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ List("idiv\n")
+  case Aop("%", a1, a2) => compile_exp(a1, env) ++ compile_exp(a2, env) ++ List("irem\n")
+  case If(b, a1, a2) => {
+    val if_else = Fresh("If_else")
+    val if_end = Fresh("If_end")
+    compile_bexp(b, env, if_else) ++
+    compile_exp(a1, env) ++
+    List("goto " + if_end + "\n") ++
+    List("\n" + if_else + ":\n\n") ++
+    compile_exp(a2, env) ++
+    List("\n" + if_end + ":\n\n")
+  }
+  case Call(n, args) => {
+    val is = "I" * args.length
+    args.flatMap(a => compile_exp(a, env)) ++
+    List ("invokestatic XXX/XXX/" + n + "(" + is + ")I\n")
+  }
+  case Sequ(a1, a2) => {
+    compile_exp(a1, env) ++ List("pop\n") ++ compile_exp(a2, env)
+  }
+  case Write(a1) => {
+    compile_exp(a1, env) ++
+    List("dup\n",
+         "invokestatic XXX/XXX/write(I)V\n")
+  }
+}
+
+// compile boolean expressions
+def compile_bexp(b: BExp, env : Env, jmp: String) : Instrs = b match {
+  case Bop("==", a1, a2) => 
+    compile_exp(a1, env) ++ compile_exp(a2, env) ++ List("if_icmpne " + jmp + "\n")
+  case Bop("!=", a1, a2) => 
+    compile_exp(a1, env) ++ compile_exp(a2, env) ++ List("if_icmpeq " + jmp + "\n")
+  case Bop("<", a1, a2) => 
+    compile_exp(a1, env) ++ compile_exp(a2, env) ++ List("if_icmpge " + jmp + "\n")
+  case Bop("<=", a1, a2) => 
+    compile_exp(a1, env) ++ compile_exp(a2, env) ++ List("if_icmpgt " + jmp + "\n")
+}
+
+// compile function for declarations and main
+def compile_decl(d: Decl) : Instrs = d match {
+  case Def(name, args, a) => { 
+    val env = args.zipWithIndex.toMap
+    val is = "I" * args.length
+    List(".method public static " + name + "(" + is + ")I \n",
+         ".limit locals " + args.length.toString + "\n",
+         ".limit stack " + (1 + max_stack_exp(a)).toString + "\n",
+         name + "_Start:\n") ++   
+    compile_exp(a, env) ++
+    List("ireturn\n",
+         ".end method \n\n")
+  }
+  case Main(a) => {
+    List(".method public static main([Ljava/lang/String;)V\n",
+         ".limit locals 200\n",
+         ".limit stack 200\n") ++
+    compile_exp(a, Map()) ++
+    List("invokestatic XXX/XXX/write(I)V\n",
+         "return\n",
+         ".end method\n")
+  }
+}
+
+// main compilation function
+def compile(prog: List[Decl], class_name: String) : String = {
+  val instructions = prog.flatMap(compile_decl).mkString
+  (library + instructions).replaceAllLiterally("XXX", class_name)
+}
+
+
+
+
+// example program (factorials)
+
+val test_prog = 
+  List(Def("fact", List("n"),
+         If(Bop("==",Var("n"),Num(0)),
+            Num(1),
+            Aop("*",Var("n"),
+                    Call("fact",List(Aop("-",Var("n"),Num(1))))))),
+
+       Def("facT",List("n", "acc"),
+         If(Bop("==",Var("n"),Num(0)),
+            Var("acc"),
+            Call("facT",List(Aop("-",Var("n"),Num(1)), 
+                             Aop("*",Var("n"),Var("acc")))))),
+
+       Main(Sequ(Write(Call("fact",List(Num(10)))),
+                 Write(Call("facT",List(Num(10), Num(1)))))))
+
+// prints out the JVM instructions
+println(compile(test, "fact"))