fix some comments

src/Analysis/Abstract/Evaluating.hs

@@ -169,7 +169,7 @@ type EvaluatingEffects term value
      , State  (EnvironmentFor value)                      -- Environments (both local and global)
      , State  (HeapFor value)                             -- The heap
      , Reader (ModuleTable [term])                        -- Cache of unevaluated modules
-     , Reader (EnvironmentFor value)                      -- Default environment used by evaluateModule
+     , Reader (EnvironmentFor value)                      -- Default environment used as a fallback in lookupEnv
      , State  (ModuleTable (EnvironmentFor value, value)) -- Cache of evaluated modules
      , State  (ExportsFor value)                          -- Exports (used to filter environments when they are imported)
      , State  (IntMap.IntMap term)                        -- For jumps

src/Control/Abstract/Evaluator.hs

@@ -56,7 +56,8 @@ class Monad m => MonadEnvironment value m | m -> value where
   -- | Retrieve the default environment.
   defaultEnvironment :: m (EnvironmentFor value)
 
-  -- | Set the default environment for the lifetime of an action
+  -- | Set the default environment for the lifetime of an action.
+  --   Usually only invoked in a top-level evaluation function.
   withDefaultEnvironment :: EnvironmentFor value -> m a -> m a
 
   -- | Get the global export state.