[clash] update Voter.hs to avoid list

haskell/Voter.hs

@@ -1,5 +1,9 @@
 module Voter where
 
+-- Can't produce verilog/vhdl: Blackbox error
+-- https://groups.google.com/g/clash-language/c/fqzkxyY5eAw?pli=1
+-- Probably because of `list' usage. Got to try vector. ✓
+
 {-
 Formal Modeling and Analysis of an Avionics Triplex Sensor Voter
  - Samar Dajani-Brown, Darren Cofer, Gary Hartmann & Steve Pratt 
@@ -24,6 +28,10 @@ data State
   | VNone
   deriving (Generic, NFDataX)
 
+countValidSens :: Vec 3 Sensor -> Int
+countValidSens sens = foldr (\s n -> if valid s then n+1 else n) 0 sens
+
+
 tooMuch :: Int -> Int -> Int -> Bool
 tooMuch limit a b =
   let val = abs $ a - b in
@@ -47,12 +55,14 @@ validSensors sens =
 
 nextState :: State -> Vec 3 Sensor -> State
 nextState VAll sens = 
-  let vsens = validSensors sens in
-  if L.length vsens < 3 then
+  if countValidSens sens < 3 then
     -- 1 sensor newly invalidated.
     -- 2 valid sensors available. No miscompare.
     -- (Assumption: No simultaneous failures)
-    V2NoMis (vsens L.!! 1) (vsens L.!! 0)
+    let s12 = if (valid $ sens !! 0) && (valid $ sens !! 1) then (0, 1)
+              else if (valid $ sens !! 0) && (valid $ sens !! 2) then (0, 2)
+              else (1, 2) in
+    V2NoMis (fst s12) (snd s12)
   else
     -- No new invalid sensor
     case isMiscomp3 sens of
@@ -63,11 +73,13 @@ nextState VAll sens =
         2 -> V2NoMis 1 2
 
 nextState (V2NoMis sid1 sid2) sens =
-  let vsens = validSensors sens in
-  if L.length vsens < 2 then
+  if countValidSens sens < 2 then
     -- 1 sensor newly invalidated.
     -- 1 valid sensor available
-    V1 (vsens L.!! 0)
+    let sid = if (valid $ sens !! 0) then 0
+              else if (valid $ sens !! 1) then 1
+              else 2 in
+    V1 sid
   else
     -- No new invalid sensor
     case tooMuch 0 (out $ sens !! sid1) (out $ sens !! sid2) of
@@ -77,9 +89,11 @@ nextState (V2NoMis sid1 sid2) sens =
       True -> V2Mis sid1 sid2
 
 nextState (V2Mis sid1 sid2) sens =
-  let vsens = validSensors sens in
-  if L.length vsens < 2 then
-    V1 (vsens L.!! 0)
+  if countValidSens sens < 2 then
+    let sid = if (valid $ sens !! 0) then 0
+              else if (valid $ sens !! 1) then 1
+              else 2 in
+    V1 sid
   else
     case tooMuch 0 (out $ sens !! sid1) (out $ sens !! sid2) of
       -- Miscompare over!
@@ -88,8 +102,7 @@ nextState (V2Mis sid1 sid2) sens =
       True -> V2Mis sid1 sid2
       
 nextState (V1 sid) sens =
-  let vsens = validSensors sens in
-  if vsens == [] then VNone
+  if countValidSens sens < 1 then VNone
   else V1 sid
 
 nextState VNone sens = VNone