String pattern handling

src/GF/Grammar/AppPredefined.hs

@@ -6,8 +6,9 @@ import Ident
 import PrGrammar (prt)
 ---- import PGrammar (pTrm)
 
--- predefined function definitions. AR 12/3/2003.
--- Type checker looks at signatures in predefined.gf
+-- predefined function type signatures and definitions. AR 12/3/2003.
+
+---- typPredefined :: Term -> Err Type
 
 appPredefined :: Term -> Term
 appPredefined t = case t of

src/GF/Grammar/PatternMatch.hs

@@ -77,6 +77,7 @@ isInConstantForm trm = case trm of
     Abs _ _  -> True
     App c a  -> isInConstantForm c && isInConstantForm a
     R r      -> all (isInConstantForm . snd . snd) r
+    K _      -> True
     Alias _ _ t -> isInConstantForm t
     _       -> False ---- isInArgVarForm trm