Fix Issue 41: "," in context-free rules causes parsing failure

The CF parser in GF.Grammar.CF assigns function names to the rules, but they
are not always unique, causing rules to be dropped in the follwing CF->GF
conversion. So a pass has been added before the CF->GF conversion, to make
sure that function names are unique.

A comment says "rules have an amazingly easy parser", but the parser looks
like quick hack. It is very sloppy and silently ignores many errors, e.g.
- Explicitly given function names should end with '.', but if the do not, the
  last character in the function name is silently dropped.
- Everything following a ';' is silently dropped.

src/compiler/GF/Grammar/CF.hs

@@ -23,12 +23,13 @@ import GF.Infra.UseIO
 import GF.Data.Operations
 import GF.Data.Utilities (nub')
 
+import qualified Data.Set as S
 import Data.Char
 import Data.List
 --import System.FilePath
 
 getCF :: FilePath -> String -> Err SourceGrammar
-getCF fpath = fmap (cf2gf fpath) . pCF
+getCF fpath = fmap (cf2gf fpath . uniqueFuns) . pCF
 
 ---------------------
 -- the parser -------
@@ -77,6 +78,21 @@ type CFItem = Either CFCat String
 type CFCat = String
 type CFFun = String
 
+
+--------------------------------
+-- make function names unique -- 
+--------------------------------
+
+uniqueFuns :: CF -> CF
+uniqueFuns = snd . mapAccumL uniqueFun S.empty
+  where
+    uniqueFun funs (L l (fun,rule)) = (S.insert fun' funs,L l (fun',rule))
+      where
+        fun' = head [fun'|suffix<-"":map show ([2..]::[Int]),
+                          let fun'=fun++suffix,
+                          not (fun' `S.member` funs)]
+
+
 --------------------------
 -- the compiler ----------
 --------------------------