Make sure error messages announce that they are, in fact, error messa…

…ges. Addresses #16.

examples/shadow-tests.dx

@@ -1,10 +1,10 @@
 
 -- repeated vars in patterns not allowed
 :p (x, x) = (1, 1); x
-> Variable redefined: x
+> Error: variable already defined: x
 
 :p f (x, x) = x; f (1, 1)
-> Variable redefined: x
+> Error: variable already defined: x
 
 -- TODO: re-enable if we choose to allow non-peer shadowing
 -- -- shouldn't cause error even though it shadows x elsewhere
@@ -21,7 +21,7 @@ arr = 10
 -- _ = 10 -- underscore shadows allowed
 
 arr = 20
-> Variable redefined: arr
+> Error: variable already defined: arr
 
 :p arr
 > 10

examples/type-tests.dx

@@ -160,4 +160,4 @@ f x =
 >       ^^
 :t x = 3
    for i::x. 0
-> Variable not in scope:type variable "x" (a term variable of the same name is in scope)
+> Error: variable not in scope: type variable "x" (a term variable of the same name is in scope)

src/lib/DeShadow.hs

@@ -119,7 +119,7 @@ freshBinderP :: BinderP a -> DeShadowCat (BinderP a)
 freshBinderP (v:>ann) = do
   shadowed <- looks $ (v `isin`) . fst . fst
   if shadowed && v /= Name "_" 0
-    then throw RepeatedVarErr (" " ++ pprint v)
+    then throw RepeatedVarErr (pprint v)
     else return ()
   v' <- looks $ rename v . snd
   extend (asFst (v@>v'), v'@>())
@@ -129,7 +129,7 @@ freshTBinder :: TBinder -> DeShadowCat TBinder
 freshTBinder (v:>k) = do
   shadowed <- looks $ (v `isin`) . snd . fst
   if shadowed && v /= Name "_" 0
-    then throw RepeatedVarErr (" " ++ pprint v)
+    then throw RepeatedVarErr (pprint v)
     else return ()
   v' <- looks $ rename v . snd
   extend (asSnd (v@>TypeVar v'), v'@>())

src/lib/JIT.hs

@@ -417,7 +417,7 @@ compileBuiltin b ts = case b of
   FDiv     -> compileBinop RealType (\x y -> L.FDiv noFastMathFlags x y [])
   FLT      -> compileBinop BoolType (\x y -> L.FCmp L.OLT x y [])
   FGT      -> compileBinop BoolType (\x y -> L.FCmp L.OGT x y [])
-  Todo     -> const $ throw OtherErr "Can't compile 'todo'"
+  Todo     -> const $ throw MiscErr "Can't compile 'todo'"
   BoolToInt -> compileUnop IntType  (\x -> L.ZExt x longTy [])
   IntToReal -> compileUnop RealType (\x -> L.SIToFP x realTy [])
   FFICall _ name -> compileFFICall name ts

src/lib/PPrint.hs

@@ -43,12 +43,11 @@ instance Pretty ErrType where
     ParseErr          -> "Parse error:"
     TypeErr           -> "Type error:"
     LinErr            -> "Linearity error:"
-    CompilerErr       -> "Compiler bug!"
-    UnboundVarErr     -> "Variable not in scope:"
-    RepeatedVarErr    -> "Variable redefined:"
+    UnboundVarErr     -> "Error: variable not in scope: "
+    RepeatedVarErr    -> "Error: variable already defined: "
     NotImplementedErr -> "Not implemented:"
-    OtherErr          -> "Error:"
-    UpstreamErr       -> "Upstream failure"
+    CompilerErr       -> "Compiler bug!"
+    MiscErr           -> "Error:"
 
 instance Pretty Type where
   pretty t = prettyTyDepth 0 t

src/lib/Syntax.hs

@@ -301,8 +301,7 @@ data ErrType = NoErr
              | RepeatedVarErr
              | CompilerErr
              | NotImplementedErr
-             | UpstreamErr
-             | OtherErr
+             | MiscErr
   deriving (Show)
 
 type Except a = Either Err a