--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/bf/bfi.sc	Tue Jul 21 00:12:34 2020 +0100
@@ -0,0 +1,85 @@
+// A simple Interpreter for BF*** Programs
+//=========================================
+//
+// Call
+//
+//  amm bfi.sc <<bf_program.bf>>
+
+
+import scala.util._
+
+// BF memory as a map
+type Mem = Map[Int, Int]
+
+// reading and writing BF memory
+def sread(mem: Mem, mp: Int) : Int = 
+  mem.getOrElse(mp, 0)
+
+def write(mem: Mem, mp: Int, v: Int) : Mem =
+  mem.updated(mp, v)
+
+
+// Right and Left Jumps in BF loops
+def jumpRight(prog: String, pc: Int, level: Int) : Int = {
+  if (prog.length <= pc) pc 
+  else (prog(pc), level) match {
+    case (']', 0) => pc + 1
+    case (']', l) => jumpRight(prog, pc + 1, l - 1)
+    case ('[', l) => jumpRight(prog, pc + 1, l + 1)
+    case (_, l) => jumpRight(prog, pc + 1, l)
+  }
+}
+
+def jumpLeft(prog: String, pc: Int, level: Int) : Int = {
+  if (pc < 0) pc 
+  else (prog(pc), level) match {
+    case ('[', 0) => pc + 1
+    case ('[', l) => jumpLeft(prog, pc - 1, l - 1)
+    case (']', l) => jumpLeft(prog, pc - 1, l + 1)
+    case (_, l) => jumpLeft(prog, pc - 1, l)
+  }
+}
+
+// main interpreter loop
+def compute(prog: String, pc: Int, mp: Int, mem: Mem) : Mem = {
+  if (0 <= pc && pc < prog.length) { 
+    val (new_pc, new_mp, new_mem) = prog(pc) match {
+      case '>' => (pc + 1, mp + 1, mem)
+      case '<' => (pc + 1, mp - 1, mem)
+      case '+' => (pc + 1, mp, write(mem, mp, sread(mem, mp) + 1))
+      case '-' => (pc + 1, mp, write(mem, mp, sread(mem, mp) - 1))
+      case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) }
+      case ',' => (pc + 1, mp, write(mem, mp, Console.in.read().toByte))
+      case '['  => if (sread(mem, mp) == 0) 
+                      (jumpRight(prog, pc + 1, 0), mp, mem) 
+                   else (pc + 1, mp, mem) 
+      case ']'  => if (sread(mem, mp) != 0) 
+                      (jumpLeft(prog, pc - 1, 0), mp, mem) 
+                   else (pc + 1, mp, mem) 
+      case _ => (pc + 1, mp, mem)
+    }		     
+    compute(prog, new_pc, new_mp, new_mem)	
+  }
+  else mem
+}
+
+def run(prog: String, m: Mem = Map()) = compute(prog, 0, 0, m)
+
+// helper code for timing information
+def time_needed[T](n: Int, code: => T) = {
+  val start = System.nanoTime()
+  for (i <- 0 until n) code
+  val end = System.nanoTime()
+  (end - start)/(n * 1.0e9)
+}
+
+// Testcases
+//===========
+
+@doc(" the argument should be a BF program ")
+@main
+def main(fname: String) = {
+  val bf_str = os.read(os.pwd / fname)
+  println(s"${time_needed(1, run(bf_str))} secs")
+}  
+