Added srg0006: A grammar with a cycle caused by an empty production.

src/GF/Speech/TransformCFG.hs

@@ -88,7 +88,7 @@ stateGFCC = mkGFCC . mkCanon2gfcc . stateGrammarST
 
 -- * Grammar filtering
 
--- | Removes all directly cyclic productions.
+-- | Removes all directly and indirectly cyclic productions.
 removeCycles :: CFRules -> CFRules 
 removeCycles = groupProds . removeCycles_ . ungroupProds
   where removeCycles_ rs = [r | r@(CFRule c rhs _) <- rs, rhs /= [Cat c]]

test/srg/srg0006/srg0006.gf

@@ -0,0 +1,10 @@
+-- A grammar with a cycle caused by an empty category.
+cat S; E;
+
+fun f : E -> S -> S;
+fun g : S ;
+fun e : E ;
+
+lin f e s = { s = e.s ++ s.s } ;
+lin g = { s = "s" } ;
+lin e = { s = [] } ;