CESK fix for imports

Author: byorgey

src/swarm-engine/Swarm/Game/CESK.hs

@@ -95,7 +95,7 @@ import Swarm.Game.Ingredients (Count)
 import Swarm.Game.Tick
 import Swarm.Game.World (WorldUpdate (..))
 import Swarm.Language.Elaborate (insertSuspend)
-import Swarm.Language.Load (SourceMap, SyntaxWithImports (..))
+import Swarm.Language.Load (SyntaxWithImports (..))
 import Swarm.Language.Requirements.Type (Requirements)
 import Swarm.Language.Syntax
 import Swarm.Language.Types
@@ -153,6 +153,9 @@ data Frame
     --   in the given environment (extended by binding the variable,
     --   if there is one, to the output of the first command).
     FBind (Maybe Var) (Maybe (Polytype, Requirements)) (Term Resolved) Env
+  | -- | We are in the process of evaluating an import; once done, we
+    --   should proceed to evaluate the given body.
+    FImport (Term Resolved)
   | -- | Apply specific updates to the world and current robot.
     --
     -- The 'Const' is used to track the original command for error messages.
@@ -425,6 +428,7 @@ prettyFrame f (p, inner) = case f of
   FExec -> prettyPrefix "E·" (p, inner)
   FBind Nothing _ t _ -> (0, pparens (p < 1) inner <+> ";" <+> ppr t)
   FBind (Just x) _ t _ -> (0, hsep [ppr x, "<-", pparens (p < 1) inner, ";", ppr t])
+  FImport t -> (11, hsep ["import", inner, "in", ppr t])
   FImmediate c _worldUpds _robotUpds -> prettyPrefix ("I[" <> ppr c <> "]·") (p, inner)
   FUpdate {} -> (p, inner)
   FFinishAtomic -> prettyPrefix "A·" (p, inner)

src/swarm-engine/Swarm/Game/State.hs

@@ -132,7 +132,7 @@ import Swarm.Game.World qualified as W
 import Swarm.Game.World.Coords
 import Swarm.Language.Load (SyntaxWithImports (..))
 import Swarm.Language.Pipeline (processSource, requireNonEmptyTerm)
-import Swarm.Language.Syntax (Phase (..), SrcLoc (..), Syntax, sLoc)
+import Swarm.Language.Syntax (Phase (..), SrcLoc (..), sLoc)
 import Swarm.Language.Value (Env)
 import Swarm.Log
 import Swarm.Util (applyWhen, uniq)

src/swarm-engine/Swarm/Game/Step.hs

@@ -739,12 +739,9 @@ stepCESK cesk = case cesk of
         -- To evaluate an import:
         --   (1) stick a 'suspend' at the end of the term
         --     corresponding to the imported module, so we can save the resulting environment
-        --   (2) push an FBind frame on the stack to continue with the
-        --     rest of the code once we're done processing the import.
-        --     Note that the environment in the FBind will be ignored
-        --     in favor of the environment resulting from the suspend.
-        --   (3) push an FExec frame to execute the import itself.
-        Just m -> In (insertSuspend $ erase m ^. sTerm) e s (FExec : FBind Nothing Nothing t e : k)
+        --   (2) push an FImport frame on the stack to continue with the
+        --     body in the context of the input once we're done processing it.
+        Just m -> In (insertSuspend $ erase m ^. sTerm) e s (FImport t : k)
   -- XXX keep a map from imports to corresponding Env, don't re-evaluate if it's already
   -- in the map.  To make this sound, need to disallow all but defs in an import.
   -- Ignore explicit parens.
@@ -817,6 +814,16 @@ stepCESK cesk = case cesk of
           Nothing -> addValueBinding x v e
           Just (ty, reqs) -> addBinding x (WithType v ty reqs) e
     return $ In t2 e' s (FExec : k)
+  -- If we have suspended at the end of an import, go ahead and
+  -- evaluate the suspend without waiting for an FExec, since the body
+  -- of the import may or may not be something we need to execute
+  -- (e.g. "import blah in x + 1" vs "import blah in move; foo")
+  Out (VSuspend t e) s (FImport body : k) -> return $ In t e s (FSuspend e : FImport body : k)
+  -- This case shouldn't happen: we will always insert a call to
+  -- 'suspend' at the end of an import, so we will reach the 'FImport'
+  -- frame in a 'Suspended' state, so we can restore the suspended
+  -- environment.
+  Out _ s (FImport _ : _) -> badMachineState s "FImport frame in non-suspended state"
   -- To execute a suspend instruction, evaluate its argument and then
   -- suspend.
   Out (VSuspend t e) s (FExec : k) -> return $ In t e s (FSuspend e : k)
@@ -852,6 +859,10 @@ stepCESK cesk = case cesk of
           Nothing -> addValueBinding x v e
           Just (ty, reqs) -> addBinding x (WithType v ty reqs) e
     return $ In t2 e' s (FExec : k)
+  -- If we we're suspended after processing an import, resume by
+  -- evaluating the body of the import in the suspended context we got
+  -- after processing the import.
+  Suspended _ e s (FImport t : k) -> return $ In t e s k
   -- Otherwise, if we're suspended with nothing else left to do,
   -- return the machine unchanged (but throw away the rest of the
   -- continuation stack).