Currently a request like the below throws an error: "java.lang.IllegalArgumentException: Endpoint name should be a constant"
```
SELECT *
WITH
{
SELECT ?link ?title ?endpoint
{
VALUES ?link { wd:Q8523541 }
[] schema:about ?link; schema:isPartOf ?ws; schema:name ?title .
MINUS { ?ws wikibase:wikiGroup "wikiquote" }
BIND( strbefore(strafter(str(?ws),"//"),"/") as ?endpoint)
}
} as %categories
WHERE
{ INCLUDE %categories
SERVICE wikibase:mwapi {
bd:serviceParam wikibase:api "Generator" .
bd:serviceParam wikibase:endpoint ?endpoint .
# bd:serviceParam wikibase:endpoint "eo.wikipedia.org" .
bd:serviceParam mwapi:gcmtitle ?title .
bd:serviceParam mwapi:generator "categorymembers" .
bd:serviceParam mwapi:gcmprop "ids|title|type" .
bd:serviceParam mwapi:gcmlimit "max" .
?article wikibase:apiOutput mwapi:title .
?item wikibase:apiOutputItem mwapi:item .
?ns wikibase:apiOutput "@ns" .
}
}
```
To query several endpoints based on sitelinks on one or several items, it would be interesting if the endpoint name could be defined in a variable.
It would avoid to list specific endpoints in lines like:
```
bd:serviceParam wikibase:endpoint "eo.wikipedia.org" .
```