How to build stream expression with StreamFactory - solr

Question

I am trying to build let expression for solr stream but it gives error saying
Caused by: java.io.IOException: Invalid stream expression col(samples,score) - function 'col' is unknown (not mapped to a valid TupleStream)
StreamFactory = new StreamFactory().withDefaultZkHost(zookeeper)
.withFunctionName("search", CloudSolrStream.class)
.withFunctionName("select", SelectStream.class)
.withFunctionName("merge", MergeStream.class)
.withFunctionName("sort", SortStream.class)
.withFunctionName("tuple", TupStream.class)
.withFunctionName("rollup", RollupStream.class)
.withFunctionName("hashJoin", HashJoinStream.class)
.withFunctionName("count", CountMetric.class)
.withFunctionName("facet", FacetStream.class)
.withFunctionName("sum", SumMetric.class)
.withFunctionName("unique", UniqueStream.class)
.withFunctionName("significantTerms", SignificantTermsStream.class)
.withFunctionName("stats", StatsStream.class)
.withFunctionName("innerJoin", InnerJoinStream.class)
.withFunctionName("issnMerge", IssnMergeStream.class)
.withFunctionName("intersect", IntersectStream.class)
.withFunctionName("boostByEra", BoostBooksByEraExpression.class)
.withFunctionName("determineRRec", DetermineRepresentativeRecord.class)
.withFunctionName("plist", ParallelListStream.class)
.withFunctionName("let", LetStream.class);
My expression is as below:
let(samples=search(wc_art,qt="/select",q="al:next AND al:generation",fq="_delete:false",fq="_namespace:default",fl="score,numdocs(),id",rows=10,fq="{!lucene q.op=OR}pa:(medline)",defType=edismax,q.op=AND,sort="score desc"),responses=col(samples,score),summary=describe(responses))

Answer 1

The col function was added in Solr 7, so if your Solr installation is older than that the function won't be available. Upgrade to a more recent version.