the GF syntax for identifiers is exteded with quoted forms, i.e. you could write for instance 'ab.c' and then everything between the quites is identifier. This includes Unicode characters and non-ASCII symbols. This is useful for automatically generated GF grammars.

src/runtime/haskell/PGF/CId.hs

@@ -7,6 +7,7 @@ module PGF.CId (CId(..),
 
 import Control.Monad
 import qualified Data.ByteString.Char8 as BS
+import qualified Data.ByteString.UTF8 as UTF8
 import Data.Char
 import qualified Text.ParserCombinators.ReadP as RP
 import qualified Text.PrettyPrint as PP
@@ -21,7 +22,7 @@ wildCId = CId (BS.singleton '_')
 
 -- | Creates a new identifier from 'String'
 mkCId :: String -> CId
-mkCId s = CId (BS.pack s)
+mkCId s = CId (UTF8.fromString s)
 
 bsCId = CId
 
@@ -33,7 +34,18 @@ readCId s = case [x | (x,cs) <- RP.readP_to_S pCId s, all isSpace cs] of
 
 -- | Renders the identifier as 'String'
 showCId :: CId -> String
-showCId (CId x) = BS.unpack x
+showCId (CId x) = 
+  let raw = UTF8.toString x
+  in if isIdent raw
+       then raw
+       else "'" ++ concatMap escape raw ++ "'"
+  where
+    isIdent []     = False
+    isIdent (c:cs) = isIdentFirst c && all isIdentRest cs
+
+    escape '\'' = "\\\'"
+    escape '\\' = "\\\\"
+    escape c    = [c]
 
 instance Show CId where
     showsPrec _ = showString . showCId
@@ -48,10 +60,35 @@ pCId = do s <- pIdent
             else return (mkCId s)
 
 pIdent :: RP.ReadP String
-pIdent = liftM2 (:) (RP.satisfy isIdentFirst) (RP.munch isIdentRest)
-  where
-    isIdentFirst c = c == '_' || isLetter c
-    isIdentRest c = c == '_' || c == '\'' || isAlphaNum c
+pIdent = 
+  liftM2 (:) (RP.satisfy isIdentFirst) (RP.munch isIdentRest)
+  `mplus`
+  do RP.char '\''
+     cs <- RP.many1 insideChar
+     RP.char '\''
+     return cs
+--  where
+insideChar = RP.readS_to_P $ \s ->
+  case s of
+	[]             -> []
+	('\\':'\\':cs) -> [('\\',cs)]
+	('\\':'\'':cs) -> [('\'',cs)]
+	('\\':cs)      -> []
+	('\'':cs)      -> []
+	(c:cs)         -> [(c,cs)]
+
+isIdentFirst c =
+  (c == '_') ||
+  (c >= 'a' && c <= 'z') ||
+  (c >= 'A' && c <= 'Z') ||
+  (c >= '\192' && c <= '\255' && c /= '\247' && c /= '\215')
+isIdentRest c = 
+  (c == '_') ||
+  (c == '\'') ||
+  (c >= '0' && c <= '9') ||
+  (c >= 'a' && c <= 'z') ||
+  (c >= 'A' && c <= 'Z') ||
+  (c >= '\192' && c <= '\255' && c /= '\247' && c /= '\215')
 
 ppCId :: CId -> PP.Doc
 ppCId = PP.text . showCId