[Haskell-cafe] HaXml and ghci unresolved symbol

[Andrea Rossato]

Il Sat, Sep 09, 2006 at 02:17:36PM +0200, Andrea Rossato ebbe a scrivere:
> probably it's me, but I cannot understand what I'm doing wrong.

Thanks to the discussion of this thread I was able to (sort of)
isolate the problem and understand why I cannot get hxml (if linked
with HaXml) to work with ghci.

It seems related to dynamic linking: I created a separated module
(Xml.hs) that imports Text.XML.HaXml and parses a xml string. I then
created a file (xml.hs) that imports Xml and prints "name", defined in
Xml.hs. The expected output should be "elementTest".

Now: if I compile Xml.hs alone it compiles without warnings or errors.
But when I try to load Xml.o with ghci I get an "unresolved symbol"
error.

If I load in ghci the file xml.hs (that imports Xml.hs), it loads
fine, but when I try to evaluate "main" I get the same "unresolved
symbol" error.

If I compile xml.hs, statically linking it to Xml.hs, I get a
perfectly working "a.out" that runs as expected.

So, I'm not able to create an object file (dynamically) linked to
HaXml. This is the reason why hxml doesn't work with ghc (and ghci)
but works perfectly with hugs. 

hxml works fine if I do not link it to HaXml (that is to say, without
using the HaXmlAdapter module).

Now, I don't know whether I should contact the HaXml author or submit
a bug report to the ghc developers wiki.

Can you please help me with this point? And, if you happen to have a
second and HaXml installed, can you reproduce my problem?

Thank you very much for your kind attention.

Below the code with the output of my attempts.
Sorry for such a long message.

Ciao
Andrea

 

Xml.hs:
-----------
module Xml where
import Text.XML.HaXml

xml = "<elementTest>This is a test</elementTest>"
doc = xmlParse "tmp" xml

elemName (Document prolog _ (Elem name _ content) _) = name
name = elemName doc
------------

xml.hs:
-----------
module Main where
import Xml

main = putStrLn name
---------

Results:
========

$ ghc --make -package HaXml Xml.hs 
Chasing modules from: Xml.hs
Compiling Xml              ( Xml.hs, Xml.o )

$ ghci -package HaXml Xml.o 
[logo]
Loading package base-1.0 ... linking ... done.
Loading package haskell98-1.0 ... linking ... done.
Loading package HaXml-1.13.1 ... linking ... done.
Loading object (static) Xml.o ... done
final link ... ghc-6.4.2: Xml.o: unknown symbol `TextziXMLziHaXmlziParse_xmlParse_closure'
ghc-6.4.2: linking extra libraries/objects failed

$ ghci -package HaXml xml.hs 
[logo]
Loading package base-1.0 ... linking ... done.
Loading package haskell98-1.0 ... linking ... done.
Loading package HaXml-1.13.1 ... linking ... done.
Skipping  Xml              ( ./Xml.hs, ./Xml.o )
Compiling Main             ( xml.hs, interpreted )
Ok, modules loaded: Main, Xml.
*Main> main
<interactive>: ./Xml.o: unknown symbol `TextziXMLziHaXmlziParse_xmlParse_closure'

*Main> :quit
Leaving GHCi.


$ ghc --make -package HaXml xml.hs 
Chasing modules from: xml.hs
Skipping  Xml              ( ./Xml.hs, ./Xml.o )
Compiling Main             ( xml.hs, xml.o )
Linking ...
$ ./a.out 
elementTest

$ ghci -package HaXml /usr/lib/ghc-6.4.2/HSHaXml.o
[logo]
Loading package base-1.0 ... linking ... done.
Loading package haskell98-1.0 ... linking ... done.
Loading package HaXml-1.13.1 ... linking ... done.
Loading object (static) /usr/lib/ghc-6.4.2/HSHaXml.o ... done
final link ... done
Prelude> :quit
Leaving GHCi.