From a15f77f060a34e2987886467752892b58ff445dc Mon Sep 17 00:00:00 2001
From: Camil Staps
Date: Thu, 8 Feb 2018 10:08:12 +0100
Subject: More meaningful error messages
---
src/SPL/Parse.hs | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)
diff --git a/src/SPL/Parse.hs b/src/SPL/Parse.hs
index 28230f8..eec7fd1 100644
--- a/src/SPL/Parse.hs
+++ b/src/SPL/Parse.hs
@@ -19,11 +19,14 @@ type Parser t = P.Parsec [Token] () t
parse :: [Token] -> Either P.ParseError Program
parse = P.parse spl "Not a valid program" . filter (not . isCommentToken)
-check :: (Token -> Maybe a) -> Parser a
-check f = P.tokenPrim show (const . const) f
+check :: String -> (Token -> Maybe a) -> Parser a
+check e f = P.tokenPrim show (\p _ _ -> P.incSourceColumn p 1) f <?> e
+-- TODO: We increment the source column to get meaningful error messages;
+-- the error that is furthest in the parsing process. We need to keep positions
+-- in the list of tokens so that we can update this properly.
token :: Token -> Parser Token
-token t = check (\u -> if t == u then Just t else Nothing)
+token t = check (show t) (\u -> if t == u then Just t else Nothing)
choice :: [Parser a] -> Parser a
choice = P.choice . map P.try
@@ -44,7 +47,7 @@ toplevel = choice
]
comment :: Parser String
-comment = check $ \case
+comment = check "comment" $ \case
TSingleComment s -> Just s
TBlockComment s -> Just s
_ -> Nothing
@@ -70,16 +73,16 @@ var = do
fun :: Parser Function
fun = do
id <- ident
- args <- parenthesised (ident `sepBy` token TComma) <?> "arguments"
- ftype <- optional (token TColonColon *> funType) <?> "optional function type"
+ args <- parenthesised (ident `sepBy` token TComma)
+ ftype <- optional (token TColonColon *> funType)
token TBraceOpen
- vars <- many (P.try var) <?> "local variables"
- stmt <- statements <?> "function body"
+ vars <- many (P.try var)
+ stmt <- statements
token TBraceClose
return $ Function id ftype args vars stmt
ident :: Parser Name
-ident = check $ \case
+ident = check "identifier" $ \case
TIdent id -> Just id
_ -> Nothing
@@ -147,7 +150,7 @@ expr =
]
literal :: Parser Expression
- literal = fmap Literal $ nil <|> (check $ \case
+ literal = fmap Literal $ nil <|> (check "literal" $ \case
TInt i -> Just (LInt i)
TBool b -> Just (LBool b)
TChar c -> Just (LChar c)
@@ -161,7 +164,7 @@ expr =
var = Var <$> ident
statements :: Parser Statement
-statements = foldr1 Seq <$> some statement <|> pure Nop
+statements = (foldr1 Seq <$> some statement <|> pure Nop) <?> "statement"
-- NOTE: we here assume that if/while blocks need not be braced, as in the
-- example function `abs`. The alternative is using `braced statements`.
@@ -184,7 +187,7 @@ statement = choice
]
field :: Parser Field
-field = token TDot *> check (\case
+field = token TDot *> check "field" (\case
TIdent "hd" -> Just Hd
TIdent "tl" -> Just Tl
TIdent "fst" -> Just Fst
--
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