Some error

gistfile1.txt

Toplevel input, characters 45-103:
Error: Illegal application (Non-functional construction): 
The expression "sprintf "<tr><td>%s</td><td>%b</td></tr>" name value" of type
 "(fix formatType (f : format) : Type :=
     match f with
     | [] => string
     | dir :: dirs =>
         match directiveType dir with
         | Some T => T -> formatType dirs
         | None => formatType dirs
         end
     end)
    [DLit "<", DLit "/", DLit "t", DLit "d", DLit ">", 
    DLit "<", DLit "/", DLit "t", DLit "r", DLit ">"]"
cannot be applied to the term
 "value" : "bool"