More sensible error types

1 files changed, 15 insertions, 11 deletions

diff --git a/src/Error.hs b/src/Error.hs
index 1363120..14b4875 100644
--- a/src/Error.hs
+++ b/src/Error.hs
@@ -4,19 +4,20 @@ import Data.List (sort)
 import Text.Parsec (SourcePos, errorPos)
 import Text.Parsec.Error (ParseError, errorMessages, showErrorMessages)
 
-data Error
-  = TypeError String SourcePos
-  | UnexpectedReturn String SourcePos
-  | Error String SourcePos
+data ErrorType = GenericError | TypeError | UnexpectedReturn | AlreadyDefined
+
+instance Enum ErrorType where
+  fromEnum GenericError = 0
+  fromEnum TypeError = 1
+  fromEnum UnexpectedReturn = 2
+  fromEnum AlreadyDefined = 3
+  toEnum _ = error "toEnum is undefined for Error"
+
+data Error = Error ErrorType String SourcePos
   deriving (Eq)
 
 instance Show Error where
-  show (Error message pos) =
-    show pos ++ " error: " ++ message
-  -- XXX: can we do this differently?
-  show (TypeError message pos) =
-    show pos ++ " error: " ++ message
-  show (UnexpectedReturn message pos) =
+  show (Error _ message pos) =
     show pos ++ " error: " ++ message
 
 showParserError :: ParseError -> String
@@ -25,7 +26,10 @@ showParserError error =
     ++ showErrorMessages "or" "unknown parser error" "   expecting" "  unexpected" "end of input" (errorMessages error)
 
 instance Ord Error where
-  compare (Error _ pos1) (Error _ pos2) = compare pos1 pos2
+  compare (Error _ _ pos1) (Error _ _ pos2) = compare pos1 pos2
+
+instance Eq ErrorType where
+  e1 == e2 = fromEnum e1 == fromEnum e2
 
 showErrorList :: [Error] -> String
 showErrorList errs = unlines $ map show (sort errs)