src/Pure/Syntax/mixfix.ML

 fun pretty_mixfix NoSyn = Pretty.str ""
   | pretty_mixfix (Mixfix (s, ps, p, _)) =
       parens (Pretty.breaks [quoted s, brackets (Pretty.commas (map int ps)), int p])
   | pretty_mixfix (Infix (s, p, _)) = parens (Pretty.breaks [keyword "infix", quoted s, int p])
   | pretty_mixfix (Infixl (s, p, _)) = parens (Pretty.breaks [keyword "infixl", quoted s, int p])
-  | pretty_mixfix (Infixr (s, p, _)) = parens (Pretty.breaks [keyword "infixl", quoted s, int p])
+  | pretty_mixfix (Infixr (s, p, _)) = parens (Pretty.breaks [keyword "infixr", quoted s, int p])
   | pretty_mixfix (Binder (s, p1, p2, _)) =
       parens (Pretty.breaks [keyword "binder", quoted s, brackets [int p1], int p2])
   | pretty_mixfix (Structure _) = parens [keyword "structure"];
 
 end;