Faster regular expression pattern matching in the grammar compiler.

The sequence operator (x+y) was implemented by splitting the string to be
matched at all positions and trying to match the parts against the two
subpatterns. To reduce the number of splits, we now estimate the minimum and
maximum length of the string that the subpatterns could match. For common
cases, where one of the subpatterns is a string of known length, like
in (x+"y") or (x + ("a"|"o"|"u"|"e")+"y"), only one split will be tried.

src/compiler/GF/Grammar/Macros.hs

@@ -483,6 +483,8 @@ composOp co trm =
    ImplArg t        -> liftM ImplArg (co t)
    _ -> return trm -- covers K, Vr, Cn, Sort, EPatt
 
+composSafePattOp op = runIdentity . composPattOp (return . op)
+
 composPattOp :: Monad m => (Patt -> m Patt) -> Patt -> m Patt
 composPattOp op patt =
   case patt of
@@ -495,6 +497,7 @@ composPattOp op patt =
     PNeg p          -> liftM  PNeg (op p)
     PAlt p1 p2      -> liftM2 PAlt (op p1) (op p2)
     PSeq p1 p2      -> liftM2 PSeq (op p1) (op p2)
+    PMSeq (_,p1) (_,p2) -> liftM2 PSeq (op p1) (op p2) -- information loss
     PRep p          -> liftM  PRep (op p)
     _               -> return patt -- covers cases without subpatterns
 
@@ -545,6 +548,7 @@ collectPattOp op patt =
     PNeg p          -> op p
     PAlt p1 p2      -> op p1++op p2
     PSeq p1 p2      -> op p1++op p2
+    PMSeq (_,p1) (_,p2) -> op p1++op p2
     PRep p          -> op p
     _               -> []     -- covers cases without subpatterns