Make a separate ADT case for each user-facing error message.

This is preparation for giving better source information in error messages.

src/dex.hs

@@ -32,6 +32,7 @@ import ConcreteSyntax (keyWordStrs, preludeImportBlock)
 import RenderHtml
 -- import Live.Terminal (runTerminal)
 import Live.Web (runWeb)
+import PPrint  hiding (hardline)
 import Core
 import Types.Core
 import Types.Imp

src/lib/AbstractSyntax.hs

@@ -58,7 +58,7 @@ import Data.Text (Text)
 import ConcreteSyntax
 import Err
 import Name
-import PPrint ()
+import PPrint
 import Types.Primitives
 import Types.Source
 import qualified Types.OpNames as P
@@ -139,7 +139,7 @@ decl ann (WithSrcs sid _ d) = WithSrcB sid <$> case d of
   CLet binder rhs -> do
     (p, ty) <- patOptAnn binder
     ULet ann p ty <$> asExpr <$> block rhs
-  CBind _ _ -> throw SyntaxErr "Arrow binder syntax <- not permitted at the top level, because the binding would have unbounded scope."
+  CBind _ _ -> throw TopLevelArrowBinder
   CDefDecl def -> do
     (name, lam) <- aDef def
     return $ ULet ann (fromSourceNameW name) Nothing (WithSrcE sid (ULam lam))
@@ -199,7 +199,7 @@ withTrailingConstraints g cont = case g of
     Nest (UAnnBinder expl (WithSrcB sid b) ann cs) bs <- withTrailingConstraints lhs cont
     s <- case b of
       UBindSource s -> return s
-      UIgnore       -> throw SyntaxErr "Can't constrain anonymous binders"
+      UIgnore       -> throw CantConstrainAnonBinders
       UBind _ _     -> error "Shouldn't have internal names until renaming pass"
     c' <- expr c
     return $   UnaryNest (UAnnBinder expl (WithSrcB sid b) ann (cs ++ [c']))
@@ -261,7 +261,7 @@ uBinder :: GroupW -> SyntaxM (UBinder c VoidS VoidS)
 uBinder (WithSrcs sid _ b) = case b of
   CLeaf (CIdentifier name) -> return $ fromSourceNameW $ WithSrc sid name
   CLeaf CHole -> return $ WithSrcB sid UIgnore
-  _ -> throw SyntaxErr "Binder must be an identifier or `_`"
+  _ -> throw UnexpectedBinder
 
 -- Type annotation with an optional binder pattern
 tyOptPat :: GroupW -> SyntaxM (UAnnBinder VoidS VoidS)
@@ -300,8 +300,7 @@ pat (WithSrcs sid _ grp) = WithSrcB sid <$> case grp of
   CLeaf (CIdentifier name) -> return $ UPatBinder $ fromSourceNameW $ WithSrc sid name
   CJuxtapose True lhs rhs -> do
     case lhs of
-      WithSrcs _ _ (CJuxtapose True _ _) ->
-        throw SyntaxErr "Only unary constructors can form patterns without parens"
+      WithSrcs _ _ (CJuxtapose True _ _) -> throw OnlyUnaryWithoutParens
       _ -> return ()
     name <- identifier "pattern constructor name" lhs
     arg <- pat rhs
@@ -313,11 +312,11 @@ pat (WithSrcs sid _ grp) = WithSrcB sid <$> case grp of
         gs' <- mapM pat gs
         return $ UPatCon (fromSourceNameW name) (toNest gs')
       _ -> error "unexpected postfix group (should be ruled out at grouping stage)"
-  _ -> throw SyntaxErr "Illegal pattern"
+  _ -> throw IllegalPattern
 
 tyOptBinder :: Explicitness -> GroupW -> SyntaxM (UAnnBinder VoidS VoidS)
 tyOptBinder expl (WithSrcs sid sids grp) = case grp of
-  CBin (WithSrc _ Pipe)  _ _     -> throw SyntaxErr "Unexpected constraint"
+  CBin (WithSrc _ Pipe)  _ _     -> throw UnexpectedConstraint
   CBin (WithSrc _ Colon) name ty -> do
     b <- uBinder name
     ann <- UAnn <$> expr ty
@@ -341,7 +340,7 @@ binderReqTy expl (WithSrcs _ _ (CBin (WithSrc _ Colon) name ty)) = do
   b <- uBinder name
   ann <- UAnn <$> expr ty
   return $ UAnnBinder expl b ann []
-binderReqTy _ _ = throw SyntaxErr $ "Expected an annotated binder"
+binderReqTy _ _ = throw ExpectedAnnBinder
 
 argList :: [GroupW] -> SyntaxM ([UExpr VoidS], [UNamedArg VoidS])
 argList gs = partitionEithers <$> mapM singleArg gs
@@ -355,7 +354,7 @@ singleArg = \case
 identifier :: String -> GroupW -> SyntaxM SourceNameW
 identifier ctx (WithSrcs sid _ g) = case g of
   CLeaf (CIdentifier name) -> return $ WithSrc sid name
-  _ -> throw SyntaxErr $ "Expected " ++ ctx ++ " to be an identifier"
+  _ -> throw $ ExpectedIdentifier ctx
 
 aEffects :: WithSrcs ([GroupW], Maybe GroupW) -> SyntaxM (UEffectRow VoidS)
 aEffects (WithSrcs _ _ (effs, optEffTail)) = do
@@ -375,7 +374,7 @@ effect (WithSrcs _ _ grp) = case grp of
     return $ URWSEffect State $ fromSourceNameW (WithSrc sid h)
   CLeaf (CIdentifier "Except") -> return UExceptionEffect
   CLeaf (CIdentifier "IO"    ) -> return UIOEffect
-  _ -> throw SyntaxErr "Unexpected effect form; expected one of `Read h`, `Accum h`, `State h`, `Except`, `IO`, or the name of a user-defined effect."
+  _ -> throw UnexpectedEffectForm
 
 aMethod :: CSDeclW -> SyntaxM (Maybe (UMethodDef VoidS))
 aMethod (WithSrcs _ _ CPass) = return Nothing
@@ -386,7 +385,7 @@ aMethod (WithSrcs src _ d) = Just . WithSrcE src <$> case d of
   CLet (WithSrcs sid _ (CLeaf (CIdentifier name))) rhs -> do
     rhs' <- ULamExpr Empty ImplicitApp Nothing Nothing <$> block rhs
     return $ UMethodDef (fromSourceNameW (WithSrc sid name)) rhs'
-  _ -> throw SyntaxErr "Unexpected method definition. Expected `def` or `x = ...`."
+  _ -> throw UnexpectedMethodDef
 
 asExpr :: UBlock VoidS -> UExpr VoidS
 asExpr (WithSrcE src b) = case b of
@@ -403,7 +402,7 @@ blockDecls :: [CSDeclW] -> SyntaxM (Nest UDecl VoidS VoidS, UExpr VoidS)
 blockDecls [] = error "shouldn't have empty list of decls"
 blockDecls [WithSrcs _ _ d] = case d of
   CExpr g -> (Empty,) <$> expr g
-  _ -> throw SyntaxErr "Block must end in expression"
+  _ -> throw BlockWithoutFinalExpr
 blockDecls (WithSrcs sid _ (CBind b rhs):ds) = do
   b' <- binderOptTy Explicit b
   rhs' <- asExpr <$> block rhs
@@ -428,15 +427,15 @@ expr (WithSrcs sid _ grp) = WithSrcE sid <$> case grp of
   -- Table constructors here.  Other uses of square brackets
   -- should be detected upstream, before calling expr.
   CBrackets gs -> UTabCon <$> mapM expr gs
-  CGivens _ -> throw SyntaxErr $ "Unexpected `given` clause"
+  CGivens _ -> throw UnexpectedGivenClause
   CArrow lhs effs rhs -> do
     case lhs of
       WithSrcs _ _ (CParens gs) -> do
         bs <- aPiBinders gs
         effs' <- fromMaybeM effs UPure aEffects
         resultTy <- expr rhs
         return $ UPi $ UPiExpr bs ExplicitApp effs' resultTy
-      _ -> throw SyntaxErr "Argument types should be in parentheses"
+      _ -> throw ArgsShouldHaveParens
   CDo b -> UDo <$> block b
   CJuxtapose hasSpace lhs rhs -> case hasSpace of
     True -> extendAppRight <$> expr lhs <*> expr rhs
@@ -459,22 +458,22 @@ expr (WithSrcs sid _ grp) = WithSrcE sid <$> case grp of
       name <- case rhs' of
         CLeaf (CIdentifier name) -> return $ FieldName name
         CLeaf (CNat i          ) -> return $ FieldNum $ fromIntegral i
-        _ -> throw SyntaxErr "Field must be a name or an integer"
+        _ -> throw BadField
       return $ UFieldAccess lhs' (WithSrc src name)
     DoubleColon   -> UTypeAnn <$> (expr lhs) <*> expr rhs
     EvalBinOp s -> evalOp s
     DepAmpersand  -> do
       lhs' <- tyOptPat lhs
       UDepPairTy . (UDepPairType ExplicitDepPair lhs') <$> expr rhs
     DepComma      -> UDepPair <$> (expr lhs) <*> expr rhs
-    CSEqual       -> throw SyntaxErr "Equal sign must be used as a separator for labels or binders, not a standalone operator"
-    Colon         -> throw SyntaxErr "Colon separates binders from their type annotations, is not a standalone operator.\nIf you are trying to write a dependent type, use parens: (i:Fin 4) => (..i)"
+    CSEqual       -> throw BadEqualSign
+    Colon         -> throw BadColon
     ImplicitArrow -> case lhs of
       WithSrcs _ _ (CParens gs) -> do
         bs <- aPiBinders gs
         resultTy <- expr rhs
         return $ UPi $ UPiExpr bs ImplicitApp UPure resultTy
-      _ -> throw SyntaxErr "Argument types should be in parentheses"
+      _ -> throw ArgsShouldHaveParens
     FatArrow      -> do
       lhs' <- tyOptPat lhs
       UTabPi . (UTabPiExpr lhs') <$> expr rhs
@@ -496,7 +495,7 @@ expr (WithSrcs sid _ grp) = WithSrcE sid <$> case grp of
         WithSrcE _ (UIntLit   i) -> UIntLit   (-i)
         WithSrcE _ (UFloatLit i) -> UFloatLit (-i)
         e -> unaryApp (mkUVar sid "neg") e
-      _ -> throw SyntaxErr $ "Prefix (" ++ pprint name ++ ") not legal as a bare expression"
+      _ -> throw $ BadPrefix $ pprint name
   CLambda params body -> do
     params' <- explicitBindersOptAnn $ WithSrcs sid [] $ map stripParens params
     body' <- block body

src/lib/Algebra.hs

@@ -27,6 +27,7 @@ import MTL1
 import Name
 import Subst
 import QueryType
+import PPrint
 import Types.Core
 import Types.Imp
 import Types.Primitives
@@ -55,7 +56,7 @@ sumUsingPolys lim (Abs i body) = do
   sumAbs <- refreshAbs (Abs i body) \(i':>_) body' -> do
     exprAsPoly body' >>= \case
       Just poly' -> return $ Abs i' poly'
-      Nothing -> throw NotImplementedErr $
+      Nothing -> throwInternal $
         "Algebraic simplification failed to model index computations:\n"
         ++ "Trying to sum from 0 to " ++ pprint lim ++ " - 1, \\"
         ++ pprint i' ++ "." ++ pprint body'

src/lib/Builder.hs

@@ -17,7 +17,6 @@ import Control.Monad.State.Strict (MonadState (..), StateT (..), runStateT)
 import qualified Data.Map.Strict as M
 import Data.Foldable (fold)
 import Data.Graph (graphFromEdges, topSort)
-import Data.Text.Prettyprint.Doc (Pretty (..))
 import Foreign.Ptr
 
 import qualified Unsafe.Coerce as TrulyUnsafe
@@ -30,6 +29,7 @@ import MTL1
 import Subst
 import Name
 import PeepholeOptimize
+import PPrint
 import QueryType
 import Types.Core
 import Types.Imp
@@ -103,18 +103,6 @@ buildScopedAssumeNoDecls cont = do
     _ -> error "Expected no decl emissions"
 {-# INLINE buildScopedAssumeNoDecls #-}
 
-withReducibleEmissions
-  :: (ScopableBuilder r m, Builder r m, HasNamesE e, SubstE AtomSubstVal e)
-  => String
-  -> (forall o' . (Emits o', DExt o o') => m o' (e o'))
-  -> m o (e o)
-withReducibleEmissions msg cont = do
-  withDecls <- buildScoped cont
-  reduceWithDecls withDecls >>= \case
-    Just t -> return t
-    _ -> throw TypeErr msg
-{-# INLINE withReducibleEmissions #-}
-
 -- === "Hoisting" top-level builder class ===
 
 -- `emitHoistedEnv` lets you emit top env fragments, like cache entries or
@@ -926,10 +914,10 @@ symbolicTangentTy elTy = lookupSourceMap "SymbolicTangent" >>= \case
   Just (UTyConVar symTanName) -> do
     return $ toType $ UserADTType "SymbolicTangent" symTanName $
       TyConParams [Explicit] [toAtom elTy]
-  Nothing -> throw UnboundVarErr $
+  Nothing -> throwInternal $
     "Can't define a custom linearization with symbolic zeros: " ++
     "the SymbolicTangent type is not in scope."
-  Just _ -> throw TypeErr "SymbolicTangent should name a `data` type"
+  Just _ -> throwInternal $ "SymbolicTangent should name a `data` type"
 
 symbolicTangentZero :: EnvReader m => SType n -> m n (SAtom n)
 symbolicTangentZero argTy = return $ toAtom $ SumCon [UnitTy, argTy] 0 UnitVal

src/lib/CheapReduction.hs

@@ -29,7 +29,7 @@ import Core
 import Err
 import IRVariants
 import Name
-import PPrint ()
+import PPrint
 import QueryTypePure
 import Types.Core
 import Types.Top

src/lib/CheckType.hs

@@ -22,7 +22,7 @@ import IRVariants
 import MTL1
 import Name
 import Subst
-import PPrint ()
+import PPrint
 import QueryType
 import Types.Core
 import Types.Primitives
@@ -56,7 +56,7 @@ affineUsed name = TyperM $ do
   case lookupNameMapE name affines of
     Just (LiftE n) ->
         if n > 0 then
-          throw TypeErr $ "Affine name " ++ pprint name ++ " used " ++ show (n + 1) ++ " times."
+          throwInternal $ "Affine name " ++ pprint name ++ " used " ++ show (n + 1) ++ " times."
         else
           put $ insertNameMapE name (LiftE $ n + 1) affines
     Nothing -> put $ insertNameMapE name (LiftE 1) affines
@@ -90,7 +90,7 @@ checkTypesEq reqTy ty = alphaEq reqTy ty >>= \case
   False -> {-# SCC typeNormalization #-} do
     alphaEq reqTy ty >>= \case
       True  -> return ()
-      False -> throw TypeErr $ pprint reqTy ++ " != " ++ pprint ty
+      False -> throwInternal $ pprint reqTy ++ " != " ++ pprint ty
 {-# INLINE checkTypesEq #-}
 
 class SinkableE e => CheckableE (r::IR) (e::E) | e -> r where
@@ -407,7 +407,7 @@ instance IRRep r => CheckableE r (Con r) where
     ProdCon xs -> ProdCon <$> mapM checkE xs
     SumCon tys tag payload -> do
       tys' <- mapM checkE tys
-      unless (0 <= tag && tag < length tys') $ throw TypeErr "Invalid SumType tag"
+      unless (0 <= tag && tag < length tys') $ throwInternal "Invalid SumType tag"
       payload' <- payload |: (tys' !! tag)
       return $ SumCon tys' tag payload'
     HeapVal -> return HeapVal
@@ -570,7 +570,7 @@ instance IRRep r => CheckableWithEffects r (MiscOp r) where
       case (destTy', sourceTy) of
         (BaseTy dbt@(Scalar _), BaseTy sbt@(Scalar _)) | sizeOf sbt == sizeOf dbt ->
           return $ BitcastOp destTy' e'
-        _ -> throw TypeErr $ "Invalid bitcast: " ++ pprint sourceTy ++ " -> " ++ pprint destTy
+        _ -> throwInternal $ "Invalid bitcast: " ++ pprint sourceTy ++ " -> " ++ pprint destTy
     UnsafeCoerce t e -> UnsafeCoerce <$> checkE t <*> renameM e
     GarbageVal t -> GarbageVal <$> checkE t
     SumTag x -> do
@@ -616,14 +616,14 @@ instance IRRep r => CheckableE r (VectorOp r) where
       TabTy _ b (BaseTy (Scalar sbt)) <- return $ getType tbl'
       i' <- i |: binderType b
       ty'@(BaseTy (Vector _ sbt')) <- checkE ty
-      unless (sbt == sbt') $ throw TypeErr "Scalar type mismatch"
+      unless (sbt == sbt') $ throwInternal "Scalar type mismatch"
       return $ VectorIdx tbl' i' ty'
     VectorSubref ref i ty -> do
       ref' <- checkE ref
       RefTy _ (TabTy _ b (BaseTy (Scalar sbt))) <- return $ getType ref'
       i' <- i |: binderType b
       ty'@(BaseTy (Vector _ sbt')) <- checkE ty
-      unless (sbt == sbt') $ throw TypeErr "Scalar type mismatch"
+      unless (sbt == sbt') $ throwInternal "Scalar type mismatch"
       return $ VectorSubref ref' i' ty'
 
 checkHof :: IRRep r => EffTy r o -> Hof r i -> TyperM r i o (Hof r o)
@@ -706,7 +706,7 @@ instance IRRep r => CheckableWithEffects r (DAMOp r) where
       checkExtends effs effAnn'
       ixTy' <- checkE ixTy
       (carry', carryTy') <- checkAndGetType carry
-      let badCarry = throw TypeErr $ "Seq carry should be a product of raw references, got: " ++ pprint carryTy'
+      let badCarry = throwInternal $ "Seq carry should be a product of raw references, got: " ++ pprint carryTy'
       case carryTy' of
         TyCon (ProdType refTys) -> forM_ refTys \case RawRefTy _ -> return (); _ -> badCarry
         _ -> badCarry
@@ -773,7 +773,7 @@ checkProject i x = case getType x of
   TyCon (DepPairTy t) | i == 1 -> do
     xFst <- reduceProj 0 x
     checkInstantiation t [xFst]
-  xTy -> throw TypeErr $ "Not a product type:" ++ pprint xTy
+  xTy -> throwInternal $ "Not a product type:" ++ pprint xTy
 
 checkTabApp :: (IRRep r) => Type r o -> Atom r o -> TyperM r i o (Type r o)
 checkTabApp ty i = do
@@ -794,7 +794,7 @@ checkInstantiation abTop xsTop = do
     checkTypesEq (getType x) (binderType b)
     rest <- applySubst (b@>SubstVal x) (Abs bs body)
     go rest xs
-  go _ _ = throw ZipErr "Wrong number of args"
+  go _ _ = throwInternal "Wrong number of args"
 
 checkIntBaseType :: Fallible m => BaseType -> m ()
 checkIntBaseType t = case t of
@@ -809,7 +809,7 @@ checkIntBaseType t = case t of
       Word32Type -> return ()
       Word64Type -> return ()
       _          -> notInt
-    notInt = throw TypeErr $
+    notInt = throwInternal $
       "Expected a fixed-width scalar integer type, but found: " ++ pprint t
 
 checkFloatBaseType :: Fallible m => BaseType -> m ()
@@ -822,13 +822,13 @@ checkFloatBaseType t = case t of
       Float64Type -> return ()
       Float32Type -> return ()
       _           -> notFloat
-    notFloat = throw TypeErr $
+    notFloat = throwInternal $
       "Expected a fixed-width scalar floating-point type, but found: " ++ pprint t
 
 checkValidCast :: (Fallible1 m, IRRep r) => Type r n -> Type r n -> m n ()
 checkValidCast (TyCon (BaseType l)) (TyCon (BaseType r)) = checkValidBaseCast l r
 checkValidCast sourceTy destTy =
-  throw TypeErr $ "Can't cast " ++ pprint sourceTy ++ " to " ++ pprint destTy
+  throwInternal $ "Can't cast " ++ pprint sourceTy ++ " to " ++ pprint destTy
 
 checkValidBaseCast :: Fallible m => BaseType -> BaseType -> m ()
 checkValidBaseCast (PtrType _) (PtrType _) = return ()
@@ -838,13 +838,13 @@ checkValidBaseCast (Scalar _) (Scalar _) = return ()
 checkValidBaseCast sourceTy@(Vector sourceSizes _) destTy@(Vector destSizes _) =
   assertEq sourceSizes destSizes $ "Can't cast " ++ pprint sourceTy ++ " to " ++ pprint destTy
 checkValidBaseCast sourceTy destTy =
-  throw TypeErr $ "Can't cast " ++ pprint sourceTy ++ " to " ++ pprint destTy
+  throwInternal $ "Can't cast " ++ pprint sourceTy ++ " to " ++ pprint destTy
 
 scalarOrVectorLike :: Fallible m => BaseType -> ScalarBaseType -> m BaseType
 scalarOrVectorLike x sbt = case x of
   Scalar _ -> return $ Scalar sbt
   Vector sizes _ -> return $ Vector sizes sbt
-  _ -> throw CompilerErr "only scalar or vector base types should occur here"
+  _ -> throwInternal $ "only scalar or vector base types should occur here"
 
 data ArgumentType = SomeFloatArg | SomeIntArg | SomeUIntArg
 

src/lib/ConcreteSyntax.hs

@@ -25,6 +25,7 @@ import Data.Void
 import Text.Megaparsec hiding (Label, State)
 import Text.Megaparsec.Char hiding (space, eol)
 
+import Err
 import Lexing
 import Types.Core
 import Types.Source