A demonstration of a problem calling showattr in HaXml

haxml_showattr_bugdemo.hs

module Main where
import Text.XML.HaXml
import Text.XML.HaXml.Posn

main :: IO ()
main = processXmlWith (hexagrams `o` tag "IChing")

hexagrams :: Content Posn -> [Content Posn]
hexagrams = html [ hbody [htable [rows `o` children `with` ( tag "hexagram")] ] ]

rows :: Content Posn -> [Content Posn]
rows f =
    let
      nodes = keep /> attr "ver" /> txt
      versions = keep /> attr "ver" /> showattr "ver" -- bails
    in hrow [hcol [versions]] f

-- Runtime error:
-- bugdemo.hs: src/Text/XML/HaXml/Combinators.hs:(136,0)-(137,79): 
-- Non-exhaustive patterns in function find
--
-- code in question (I think)
-- http://hackage.haskell.org/packages/archive/HaXml/1.20.2/doc/html/src/Text-XML-HaXml-Combinators.html#find 
-- 
-- find :: String -> (String->CFilter i) -> CFilter i
-- find key cont c@(CElem (Elem _ as _) _) = cont (show (lookfor key as)) c
--   where lookfor x = fromMaybe (error ("missing attribute: "++show x)) . lookup x
-- -- 'lookfor' has the more general type :: (Eq a,Show a) => a -> [(a,b)] -> b 
--
-- HaXml: Latest version installed: 1.20.2

-- input document
{-
<?xml version="1.0"?>
<IChing>
    <hexagram>
      <number>1</number>
      <name ver="1.1">Ch'ien</name>
    </hexagram>
    <hexagram>
      <number>2</number>
      <name ver="2.2">K'un</name>
    </hexagram>
</IChing>
-}