Fix bare identifier able to start with keyword

Fix #184

src/Nirum/Parser.hs

@@ -33,30 +33,12 @@ module Nirum.Parser ( Parser
 
 import Control.Applicative ((<$>))
 import Control.Monad (join, void)
-import Data.List (foldl1')
 import qualified System.IO as SIO
 
-import Data.Set (elems)
+import Data.Set hiding (empty, foldl, fromList, map)
 import qualified Data.Text as T
 import qualified Data.Text.IO as TIO
-import Text.Megaparsec ( Token
-                       , choice
-                       , eof
-                       , many
-                       , manyTill
-                       , notFollowedBy
-                       , option
-                       , optional
-                       , runParser
-                       , sepBy1
-                       , sepEndBy
-                       , sepEndBy1
-                       , skipMany
-                       , skipSome
-                       , try
-                       , (<|>)
-                       , (<?>)
-                       )
+import Text.Megaparsec hiding (ParseError, label, parse)
 import Text.Megaparsec.Char ( char
                             , eol
                             , noneOf
@@ -129,12 +111,14 @@ identifier :: Parser Identifier
 identifier =
     quotedIdentifier <|> bareIdentifier <?> "identifier"
   where
-    keywords :: Parser String
-    keywords = foldl1' (<|>) $ map (string' . toString) $ elems reservedKeywords
     bareIdentifier :: Parser Identifier
-    bareIdentifier = do
-        notFollowedBy keywords
-        identifierRule
+    bareIdentifier = try $ do
+        ident <- lookAhead identifierRule
+        if ident `member` reservedKeywords
+            then fail $ "\"" ++ toString ident ++ "\" is a reserved keyword; "
+                        ++ "wrap it with backquotes to use it as a normal "
+                        ++ "identifier (i.e. \"`" ++ toString ident ++ "`\")"
+            else identifierRule
     quotedIdentifier :: Parser Identifier
     quotedIdentifier = do
         char '`'

test/Nirum/ParserSpec.hs

@@ -134,6 +134,9 @@ spec = do
                 identifier' "valid-identifier"
             parse' "valid_identifier" `shouldBeRight`
                 identifier' "valid_identifier"
+        it "can parse even if a keyword is a prefix of identifier" $ do
+            parse' "enumeration" `shouldBeRight` identifier' "enumeration"
+            parse' "types" `shouldBeRight` identifier' "types"
         it "can parse reserved keywords iff they are quoted" $
             forM_ keywords $ \ kwd ->
                 parse' ('`' `T.cons` kwd `T.snoc` '`') `shouldBeRight`
@@ -642,8 +645,8 @@ record dup (
     text c/b,
 );|] 5 1
         it "fails to parse if there's no space between field type and name" $ do
-            expectError "record a (typename);" 1 11
-            expectError "record a (typename\n#docs\n);" 1 11
+            expectError "record a (texta);" 1 16
+            expectError "record a (textb\n#docs\n);" 2 1
         it "fails to parse if trailing semicolon is missing" $ do
             let (_, expectErr) = helperFuncs P.module'
             expectErr