[erlang-questions] Rant: I hate parsing XML with Erlang

Hakan Mattsson <>
Tue Oct 23 16:47:46 CEST 2007


On Tue, 23 Oct 2007, Joel Reymont wrote:

JR> Take a look at the following [1] and try to visualize an  
JR> implementation in Erlang. More thoughts after the example.
JR> 
JR> The data:
JR> 
JR> <Export>
JR>    <Product>
JR>      <SKU>403276</SKU>
JR>      <ItemName>Trivet</ItemName>
JR>      <CollectionNo>0</CollectionNo>
JR>      <Pages>0</Pages>
JR>    </Product>
JR> </Export>
JR> 
JR> The Ruby hPricot code:
JR> 
JR> FIELDS = %w[SKU ItemName CollectionNo Pages]
JR> 
JR> doc = Hpricot.parse(File.read("my.xml"))
JR> (doc/:product).each do |xml_product|
JR>    product = Product.new
JR>    for field in FIELDS
JR>      product[field] = (xml_product/field.intern).first.innerHTML
JR>    end
JR>    product.save
JR> end

At a first glance your Ruby code looks impressively
compact.  But the corresponding implementation in
Erlang is about the same size. What's the point in
adding some syntactic sugar in order to make it even
more compact? It is just a matter of taste.

    % cat product.erl
    -module(product).
    -compile(export_all).
    -include_lib("xmerl/include/xmerl.hrl").
    
     parse(File) ->
        {#xmlElement{content = Exports}, _} = xmerl_scan:file(File),
        [{Tag, Val} || #xmlElement{content = Products} <- Exports,
                       #xmlElement{content = Fields} <- Products,
                       #xmlText{parents = [{Tag, _} | _], value = Val}  <- Fields].
    
    % erl
    Erlang (BEAM) emulator version 5.5.5 [source] [async-threads:0] [kernel-poll:false]
    
    Eshell V5.5.5  (abort with ^G)
    1> product:parse("my.xml").
    [{'SKU',"403276"},{'ItemName',"Trivet"},{'CollectionNo',"0"},{'Pages',"0"}]
    2> 

/Håkan


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