Rename return to pure (#2285)

Closes #700.

The most interesting changes are in `swarm-lang/Swarm/Language/Parser/{Lex,Term}.hs`, where I remove the code for parsing swarm-0.5 and add an option to parse swarm-0.6 with `return` instead of `pure`, so `swarm format --v0.6` can be used to auto-convert code using `return` to code using `pure`.

Let me know how you feel about this change!  Another possible choice would be to leave `return` as a synonym for `pure`.  I could be convinced to do that as well.

app/game/Main.hs

@@ -94,7 +94,7 @@ cliParser =
   widthOpt = option auto (long "width" <> metavar "COLUMNS" <> help "Use layout with maximum width")
 
   langVer :: Parser LanguageVersion
-  langVer = flag SwarmLangLatest SwarmLang0_5 (long "v0.5" <> help "Read (& convert) code from Swarm version 0.5")
+  langVer = flag SwarmLangLatest SwarmLang0_6 (long "v0.6" <> help "Read (& convert) code from Swarm version 0.6")
 
   printKeyMode :: Parser KeybindingPrint
   printKeyMode =

data/entities.yaml

@@ -1180,14 +1180,14 @@
     - "A rubber band can tie multiple commands together so that other robots can't execute commands in between them.  It can be used via the `atomic` command. For example, suppose robot A executes the following code:"
     - |
       ```
-      b <- ishere "rock"; if b {grab; return ()} {}
+      b <- ishere "rock"; if b {grab; pure ()} {}
       ```
     - "This seems like a safe way to execute `grab` only when there is a rock to grab.  However, it is actually possible for the `grab` to fail, if some other robot B snatches the rock right after robot A sensed it and before robot A got around to grabbing it on the next game tick."
     - "This will make robot A very sad and it will crash."
     - "To prevent this situation, robot A can wrap the commands in `atomic`, like so:"
     - |
       ```
-      atomic (b <- ishere "rock"; if b {grab; return ()} {})
+      atomic (b <- ishere "rock"; if b {grab; pure ()} {})
       ```
   properties: [pickable]
   capabilities: [atomic]

data/scenarios/Challenges/2048.yaml

@@ -9,11 +9,11 @@ objectives:
     condition: |
       try {
         as base {has "2048"}
-      } { return false }
+      } { pure false }
 solution: |
   def makeN : Int -> Cmd Unit = \n.
     if (n == 1)
-      {harvest; return ()}
+      {harvest; pure ()}
       {makeN (n/2); makeN (n/2); make (format n)}
   end;
   place "1";

data/scenarios/Challenges/Mazes/easy_cave_maze.yaml

@@ -46,7 +46,7 @@ robots:
     system: true
     program: |
       def until = \c. b <- c; if b {} {until c} end;
-      until (d <- scan down; return (d == inl ()));
+      until (d <- scan down; pure (d == inl ()));
       create "goal"
 known: [water]
 entities:

data/scenarios/Challenges/Mazes/easy_spiral_maze.yaml

@@ -46,7 +46,7 @@ robots:
     system: true
     program: |
       def until = \c. b <- c; if b {} {until c} end;
-      until (d <- scan down; return (d == inl ()));
+      until (d <- scan down; pure (d == inl ()));
       create "goal"
 entities:
   - name: wall

data/scenarios/Challenges/Mazes/invisible_maze.yaml

@@ -10,17 +10,17 @@ objectives:
       try {
         teleport self (27, -17);
         b <- ishere "goal";
-        return (not b)
-      } { return false }
+        pure (not b)
+      } { pure false }
 solution: |
   def tL = turn left end;
   def tR = turn right end;
   def ifC = \test. \then. \else. b <- test; if b then else end;
   def forever = \c. c ; forever c end;
-  def rightBlocked = tR; b <- blocked; tL; return b end;
+  def rightBlocked = tR; b <- blocked; tL; pure b end;
   def mazeStep = ifC rightBlocked {ifC blocked {tL} {move}} {tR; move} end;
   build {
-    forever (mazeStep; ifC (ishere "goal") {grab; return ()} {})
+    forever (mazeStep; ifC (ishere "goal") {grab; pure ()} {})
   }
 robots:
   - name: base

data/scenarios/Challenges/Mazes/loopy_maze.yaml

@@ -10,8 +10,8 @@ objectives:
       try {
         teleport self (27, -17);
         b <- ishere "goal";
-        return (not b)
-      } { return false }
+        pure (not b)
+      } { pure false }
 solution: |
   run "scenarios/Challenges/Mazes/loopy_maze_sol.sw"
 robots:

data/scenarios/Challenges/Mazes/loopy_maze_sol.sw

@@ -3,7 +3,7 @@ def tR = turn right end;
 def tB = turn back end;
 def ifM = \p.\t.\e. b <- p; if b t e end;
 def DFS =
-  ifM (ishere "goal") {grab; return ()} {};
+  ifM (ishere "goal") {grab; pure ()} {};
   ifM (ishere "rock") {} {
     place "rock";
     tL; b <- blocked; if b {} {move; DFS};

data/scenarios/Challenges/Ranching/_beekeeping/queenbee.sw

@@ -37,7 +37,7 @@ def moveTuple = \tup.
 
 def randomDir =
     r <- random 4;
-    return $ if (r == 1) {north}
+    pure $ if (r == 1) {north}
         $ elif (r == 2) {west}
         $ elif (r == 3) {south}
         $ else {east};
@@ -136,7 +136,7 @@ def takeStepTowardItem = \item.
         // another bee gets here first
         try {
             harvest;
-            return ();
+            pure ();
         } {};
     } {
         // Include some random motion
@@ -159,7 +159,7 @@ def workerProgram = \structureLoc.
         goToHive structureLoc;
     } {
         takeStepTowardItem "wildflower";
-        return ();
+        pure ();
     };
     workerProgram structureLoc;
     end;
@@ -206,15 +206,15 @@ def createWorkerForStructure = \loc.
         require 1 "wax gland";
         workerProgramInit beename loc;
     };
-    return ();
+    pure ();
     end;
 
 def associateHive = \loc.
    let beename = mkBeeName loc in
    try {
        // Fails if the robot does not exist
        robotnamed beename;
-       return ();
+       pure ();
    } {
        createWorkerForStructure loc;
 
@@ -227,7 +227,7 @@ def associateHive = \loc.
 
 def mapM_ : (a -> Cmd b) -> (rec l. Unit + a * l) -> Cmd Unit = \f. \l.
   case l
-    (\_. return ())
+    (\_. pure ())
     (\cons. f (fst cons); mapM_ f (snd cons))
   end;
 

data/scenarios/Challenges/Ranching/_beekeeping/solution.sw

@@ -113,14 +113,14 @@ def collectContiguous = \maxdist. \item. \hadFound. \dist.
             collectContiguous maxdist item true $ dist + 1;
         } {
             if hadFound {
-                return dist;
+                pure dist;
             } {
                 move;
                 collectContiguous maxdist item false $ dist + 1;
             }
         }
     } {
-        return dist;
+        pure dist;
     }
     end;
 
@@ -148,7 +148,7 @@ def collectAllHoneycombs = \targetCount.
 
         collectAllHoneycombs targetCount;
     } {
-        return currentCount;
+        pure currentCount;
     };
     end;
 
@@ -176,7 +176,7 @@ def pickRock =
     isRock <- ishere "rock";
     if isRock {
         grab;
-        return ();
+        pure ();
     } {};
     end;
 

data/scenarios/Challenges/Ranching/_capture/opponent.sw

@@ -41,9 +41,9 @@ def countBlocked = \n.
         isBlocked <- blocked;
         turn left;
         lastCount <- countBlocked $ n - 1;
-        return $ lastCount + boolToInt isBlocked;
+        pure $ lastCount + boolToInt isBlocked;
     } {
-        return 0;
+        pure 0;
     }
     end;
 
@@ -54,7 +54,7 @@ def reWatch =
 def locationIsOpen =
     emptyHere <- isempty;
     blockedCount <- countBlocked 4;
-    return $ emptyHere && blockedCount == 0;
+    pure $ emptyHere && blockedCount == 0;
     end;
 
 def faceAwayFrom = \loc.
@@ -84,7 +84,7 @@ def relocateAway =
     findOpenArea;
     try {
         swap marker;
-        return ();
+        pure ();
     } {
         place marker;
     };

data/scenarios/Challenges/Ranching/_fishing/hauler.sw

@@ -20,13 +20,13 @@ def isEnclosureFull : Int * Int -> Cmd Bool = \encl.
     let notFull = c < area in
 
     teleport self prevLoc;
-    return $ not notFull;
+    pure $ not notFull;
     end;
 
 def any : (a -> Cmd Bool) -> (rec l. Unit + a * l) -> Cmd Bool = \p. \l.
   case l
-    (\_. return false)
-    (\c. b <- p (fst c); if b {return true} {any p (snd c)})
+    (\_. pure false)
+    (\c. b <- p (fst c); if b {pure true} {any p (snd c)})
 end;
 
 def isEitherEnclosureFull =
@@ -37,7 +37,7 @@ def isEitherEnclosureFull =
 def tryGrab =
     try {
         grab;
-        return ()
+        pure ()
     } {};
     end;
 

data/scenarios/Challenges/Ranching/_fishing/solution.sw

@@ -17,7 +17,7 @@ def makeRoll =
 def checkIngredients =
     hasTuna <- has "crab";
     hasSeaweed <- has "seaweed";
-    return $ hasTuna && hasSeaweed;
+    pure $ hasTuna && hasSeaweed;
     end;
 
 def catchFish = \rod.
@@ -39,9 +39,9 @@ Precondition:
 At the top-right corner
 */
 def harvestRectangle =
-    intersperse 4 move $ harvest; return ();
+    intersperse 4 move $ harvest; pure ();
     turnAround left;
-    intersperse 4 move $ harvest; return ();
+    intersperse 4 move $ harvest; pure ();
     end;
 
 def harvestIngredients =
@@ -64,8 +64,8 @@ def harvestIngredients =
 
 def find : (a -> Cmd Bool) -> (rec l. Unit + a * l) -> Cmd (Unit + a) = \p. \l.
   case l
-    (\_. return (inl ()))
-    (\cons. h <- p (fst cons); if h {return $ inr (fst cons)} {find p (snd cons)})
+    (\_. pure (inl ()))
+    (\cons. h <- p (fst cons); if h {pure $ inr (fst cons)} {find p (snd cons)})
 end
 
 def tryPlace = \item.
@@ -108,7 +108,7 @@ def placeSerpentine = \placeFunc.
 
     end;
 
-def returnToCorner =
+def pureToCorner =
     turn back;
     move; move;
     turn right;
@@ -143,7 +143,7 @@ def burnTires =
 
         intersperse 2 move $ (
             placeSerpentine $ tryPlace "car tire";
-            returnToCorner;
+            pureToCorner;
             ignite forward;
 
             turn right;

data/scenarios/Challenges/Ranching/_gated-paddock/enclosure-checking.sw

@@ -1,14 +1,14 @@
 def isBlockedOrFenced =
     b <- blocked;
-    return b;
+    pure b;
     end;
 
 def checkIsEnclosed =
     maybePath <- path (inL ()) (inR "water");
-    case maybePath (\_. return True) (\_. return False);
+    case maybePath (\_. pure True) (\_. pure False);
     end;
 
-def boolToInt = \b. if (b) {return 1} {return 0}; end;
+def boolToInt = \b. if (b) {pure 1} {pure 0}; end;
 
 def countAdjacentBlockages =
 
@@ -28,7 +28,7 @@ def countAdjacentBlockages =
     b4 <- isBlockedOrFenced;
     c4 <- boolToInt b4;
 
-    return $ c1 + c2 + c3 + c4;
+    pure $ c1 + c2 + c3 + c4;
     end;
 
 // Step forward, observing left and right.
@@ -44,7 +44,7 @@ def observeLeftAndRight =
 
     turn right;
     move;
-    return $ val1 + val2;
+    pure $ val1 + val2;
     end;
 
 
@@ -65,7 +65,7 @@ def countDiagonalBlockages =
     // Second, step to both sides
     fwdCount <- observeLeftAndRight;
     backCount <- observeLeftAndRight;
-    return $ fwdCount + backCount;
+    pure $ fwdCount + backCount;
     end;
 
 def isStandingOnBridge =
@@ -74,12 +74,12 @@ def isStandingOnBridge =
     if (onFence || onGate) {
         adjCount <- countAdjacentBlockages;
         if (adjCount > 1) {
-            return true;
+            pure true;
         } {
             diagCount <- countDiagonalBlockages;
-            return $ (adjCount + diagCount) > 1;
+            pure $ (adjCount + diagCount) > 1;
         };
-    } {return false};
+    } {pure false};
     end;
 
 def getValForSheepIndex = \predicateCmd. \i.
@@ -91,15 +91,15 @@ def getValForSheepIndex = \predicateCmd. \i.
 
         boolToInt didSucceed;
     } {
-        return 0;
+        pure 0;
     }
     end;
 
 def countSheepWith = \predicateCmd.
     val1 <- getValForSheepIndex predicateCmd 1;
     val2 <- getValForSheepIndex predicateCmd 2;
     val3 <- getValForSheepIndex predicateCmd 3;
-    return $ val1 + val2 + val3;
+    pure $ val1 + val2 + val3;
     end;
 
 justFilledGap <- as base {
@@ -108,7 +108,7 @@ justFilledGap <- as base {
 
 if (justFilledGap) {
     enclosedCount <- countSheepWith checkIsEnclosed;
-    return $ enclosedCount >= 1;
+    pure $ enclosedCount >= 1;
 } {
-    return false;
+    pure false;
 }