From 777133c94a985539a0226856b606f2a845dcf503 Mon Sep 17 00:00:00 2001
From: Francesco Minnocci <ad17fmin@uwcad.it>
Date: Wed, 27 Apr 2022 12:57:33 +0200
Subject: [PATCH] Add lab7

---
 lab7/Program.fs | 99 +++++++++++++++++++++++++++++++++++++++++++++++++
 ludo/Program.fs |  2 +-
 2 files changed, 100 insertions(+), 1 deletion(-)
 create mode 100644 lab7/Program.fs

diff --git a/lab7/Program.fs b/lab7/Program.fs
new file mode 100644
index 0000000..d7d4a4c
--- /dev/null
+++ b/lab7/Program.fs
@@ -0,0 +1,99 @@
+type aexp =
+  AEint of int
+  | AEplus of (aexp * aexp)
+  | AEminus of (aexp * aexp)
+  | AEtimes of (aexp * aexp)
+
+// funzione di interpretazione
+let rec aexp_to_string : aexp -> string =
+  fun e ->
+    match e with
+      AEint i -> sprintf "%d" i
+      | AEplus (e,f) -> sprintf "(%s + %s)" (aexp_to_string e) (aexp_to_string f)
+      | AEminus (e,f) -> sprintf "(%s - %s)" (aexp_to_string e) (aexp_to_string f)
+      | AEtimes (e,f) -> sprintf "(%s * %s)" (aexp_to_string e) (aexp_to_string f)
+
+(* printfn "%s" (aexp_to_string (AEplus ((AEint 10),(AEint 6)))) *)
+
+// semantic domain
+type eval = int
+
+// error handling
+let negativeError () = failwith "natural numbers should be positive or zero"
+
+// denotational semantics
+let rec sem : aexp -> eval =
+  fun ae ->
+    match ae with
+    AEint i ->
+      if i < 0 then negativeError () else i
+   | AEplus (e,f) ->
+     sem e + sem f
+   | AEminus (e,f) ->
+     sem e - sem f
+   | AEtimes (e,f) ->
+     sem e * sem f
+
+(* printfn "%d" (sem (AEplus ((AEint 10),(AEint 6)))) *)
+
+let eval_to_string : eval -> string =
+  fun e -> Printf.sprintf "%d" e
+
+let eval : aexp -> unit =
+  fun ae ->
+    printfn "%s ==> " (aexp_to_string ae);
+    try
+      printfn "%s\n" (eval_to_string (sem ae))
+    with
+      Failure message ->
+      printfn "error: %s\n" message
+
+printfn "%A" (eval (AEplus ((AEint 10),(AEint 6))))
+
+// parallel computation
+open System.Threading
+open System.Threading.Tasks
+
+// esempio di funzioni parallele
+let runTasks () =
+  let rnd = System.Random()
+
+  for i = 1 to 10 do
+    let t = new Task(fun () ->
+      let time = rnd.Next(3000)
+      Thread.Sleep time
+      printfn "Thread %d waited for %d milliseconds" i time
+    )
+    t.Start()
+
+// il risultato non è deterministico
+let parallelIncrement () =
+  let a = [| 0 |]
+  for i = 1 to 100 do
+    let t = new Task(fun () ->
+      Thread.Sleep 100
+      a[0] <- a[0] + 1
+      printfn "Thread %d done" i
+    )
+    t.Start()
+  a
+
+// usiamo lock per fixare il problema della lettura concorrente
+// di una cella di memoria da parte di più "thread"
+let parIncr2 () =
+  let rnd = System.Random()
+  let a = [| 0 |]
+
+  Array.Parallel.iter (fun i ->
+    lock a (fun () ->
+      let x = a[0]
+      Thread.Sleep (rnd.Next 10)
+      a[0] <- x + 1
+      printfn "Thread %d done" i
+    )
+  ) [| 1 .. 1000 |]
+  a
+
+printfn "%A" (parIncr2 ())
+
+// però, la lock non risolve problemi con più risorse (i.e. dining philosophers problem)
diff --git a/ludo/Program.fs b/ludo/Program.fs
index 9708eb6..360e254 100644
--- a/ludo/Program.fs
+++ b/ludo/Program.fs
@@ -36,7 +36,7 @@ let rec sumFirstFun f k =
 let rec fold g f k1 k2 z =
   if (k2 < k1) then z
   else g (fold g f (k1+1) k2 z) (f(k1))
-
+>
 let sum x y = x + y
 let double x = 2*x