Single expression to get combined parent+child attributes?

Suppose I have a document like this:

<sentence group="A">
  <word type="1"/>
  <word type="2"/>
</sentence>
<sentence group="B">
  <word type="1"/>
</sentence>

...and I want output like this:

"A-1"
"A-2"
"B-1"

Is there a single xpath expression that would return this? Note the exact form of output is not essential, the main thing is the combination of parent-child attributes.

EDIT: My question really should have included desired xpath version, which in my case unfortunately is 1.0. So I accepted @Michael Kay's answer that clarified that it cannot be done in version 1.0.

Note @Fravadona's suggestion might work for xpath 2.0.

I don't think this can be done in XPath 1.0, for the following reasons:

• XPath 1.0 does not have a data type for a set or sequence of strings
• You can't return the result as a nodeset because the values you want in the result are not the values of nodes that exist in the input
• XPath 1.0 does not have a function like string-join to form a single string from a set of input strings.

@Fravadona has supplied an answer that will work in XPath 2.0.

If you can use XPath 2.0 then the following expression should do what you want:

//word/concat(parent::sentence/@group,"-",@type)

for each word node, concatenate:

• the group attribute of its sentence parent-node
• a dash
• its type attribute.