Removes GraphPattern::Sequence

Redundant with GraphPattern::Join.
Let's keep optimization related structs in the evaluation plan.

lib/src/sparql/plan_builder.rs

@@ -69,20 +69,6 @@ impl<'a> PlanBuilder<'a> {
                 object: self.pattern_value_from_term_or_variable(object, variables),
                 graph_name: graph_name.clone(),
             },
-            GraphPattern::Sequence(elements) => elements
-                .iter()
-                .map(|e| self.build_for_graph_pattern(e, variables, graph_name))
-                .reduce(|left, right| {
-                    Ok(PlanNode::ForLoopJoin {
-                        left: Rc::new(left?),
-                        right: Rc::new(right?),
-                    })
-                })
-                .unwrap_or_else(|| {
-                    Ok(PlanNode::StaticBindings {
-                        tuples: vec![EncodedTuple::with_capacity(variables.len())],
-                    })
-                })?,
             GraphPattern::Join { left, right } => PlanNode::HashJoin {
                 left: Rc::new(self.build_for_graph_pattern(left, variables, graph_name)?),
                 right: Rc::new(self.build_for_graph_pattern(right, variables, graph_name)?),

spargebra/src/algebra.rs

@@ -522,9 +522,6 @@ pub enum GraphPattern {
         path: PropertyPathExpression,
         object: TermPattern,
     },
-    /// A set of SPARQL patterns that can be evaluated sequentially
-    /// It is a safe case of [Join](https://www.w3.org/TR/sparql11-query/#defn_algJoin)
-    Sequence(Vec<GraphPattern>),
     /// [Join](https://www.w3.org/TR/sparql11-query/#defn_algJoin)
     Join { left: Box<Self>, right: Box<Self> },
     /// [LeftJoin](https://www.w3.org/TR/sparql11-query/#defn_algLeftJoin)
@@ -613,14 +610,6 @@ impl GraphPattern {
                 object.fmt_sse(f)?;
                 write!(f, ")")
             }
-            Self::Sequence(elements) => {
-                write!(f, "(sequence")?;
-                for e in elements {
-                    write!(f, " ")?;
-                    e.fmt_sse(f)?;
-                }
-                write!(f, ")")
-            }
             Self::Join { left, right } => {
                 write!(f, "(join ")?;
                 left.fmt_sse(f)?;
@@ -815,12 +804,6 @@ impl fmt::Display for GraphPattern {
                 path,
                 object,
             } => write!(f, "{} {} {} .", subject, path, object),
-            Self::Sequence(elements) => {
-                for e in elements {
-                    write!(f, "{} ", e)?;
-                }
-                Ok(())
-            }
             Self::Join { left, right } => {
                 if matches!(
                     right.as_ref(),
@@ -963,11 +946,6 @@ impl GraphPattern {
                     lookup_triple_pattern_variables(o, callback)
                 }
             }
-            Self::Sequence(elements) => {
-                for e in elements {
-                    e.lookup_in_scope_variables(callback);
-                }
-            }
             Self::Join { left, right }
             | Self::LeftJoin { left, right, .. }
             | Self::Union { left, right } => {

spargebra/src/parser.rs

@@ -277,7 +277,10 @@ fn build_bgp(patterns: Vec<TripleOrPathPattern>) -> GraphPattern {
     if !bgp.is_empty() {
         elements.push(GraphPattern::Bgp { patterns: bgp });
     }
-    new_sequence(elements)
+    elements
+        .into_iter()
+        .reduce(new_join)
+        .unwrap_or_else(GraphPattern::default)
 }
 
 enum TripleOrPathPattern {
@@ -368,38 +371,15 @@ fn new_join(l: GraphPattern, r: GraphPattern) -> GraphPattern {
         }
     }
 
-    // Some optimizations
-    // TODO: move to a specific optimizer pass
     match (l, r) {
         (GraphPattern::Bgp { patterns: mut pl }, GraphPattern::Bgp { patterns: pr }) => {
             pl.extend(pr);
             GraphPattern::Bgp { patterns: pl }
         }
-        (GraphPattern::Sequence(mut e1), GraphPattern::Sequence(e2)) => {
-            e1.extend_from_slice(&e2);
-            GraphPattern::Sequence(e1)
-        }
-        (GraphPattern::Sequence(mut e), r)
-            if matches!(r, GraphPattern::Bgp { .. } | GraphPattern::Path { .. }) =>
+        (GraphPattern::Bgp { patterns }, other) | (other, GraphPattern::Bgp { patterns })
+            if patterns.is_empty() =>
         {
-            e.push(r);
-            GraphPattern::Sequence(e)
-        }
-        (l, GraphPattern::Sequence(mut e))
-            if matches!(l, GraphPattern::Bgp { .. } | GraphPattern::Path { .. }) =>
-        {
-            e.insert(0, l);
-            GraphPattern::Sequence(e)
-        }
-        (
-            GraphPattern::Graph { name: g1, inner: l },
-            GraphPattern::Graph { name: g2, inner: r },
-        ) if g1 == g2 => {
-            // We merge identical graphs
-            GraphPattern::Graph {
-                name: g1,
-                inner: Box::new(new_join(*l, *r)),
-            }
+            other
         }
         (l, r) => GraphPattern::Join {
             left: Box::new(l),
@@ -408,14 +388,6 @@ fn new_join(l: GraphPattern, r: GraphPattern) -> GraphPattern {
     }
 }
 
-fn new_sequence(elements: Vec<GraphPattern>) -> GraphPattern {
-    match elements.len() {
-        0 => GraphPattern::default(),
-        1 => elements.into_iter().next().unwrap(),
-        _ => GraphPattern::Sequence(elements),
-    }
-}
-
 fn not_empty_fold<T>(
     iter: impl Iterator<Item = T>,
     combine: impl Fn(T, T) -> T,
@@ -1219,14 +1191,14 @@ parser! {
 
         //[40]
         rule DeleteWhere() -> Vec<GraphUpdateOperation> = i("DELETE") _ i("WHERE") _ d:QuadPattern() {?
-            let pattern = new_sequence(d.iter().map(|q| {
+            let pattern = d.iter().map(|q| {
                 let bgp = GraphPattern::Bgp { patterns: vec![TriplePattern::new(q.subject.clone(), q.predicate.clone(), q.object.clone())] };
                 match &q.graph_name {
                     GraphNamePattern::NamedNode(graph_name) => GraphPattern::Graph { name: graph_name.clone().into(), inner: Box::new(bgp) },
                     GraphNamePattern::DefaultGraph => bgp,
                     GraphNamePattern::Variable(graph_name) => GraphPattern::Graph { name: graph_name.clone().into(), inner: Box::new(bgp) },
                 }
-            }).collect());
+            }).reduce(new_join).unwrap_or_else(GraphPattern::default);
             let delete = d.into_iter().map(GroundQuadPattern::try_from).collect::<Result<Vec<_>,_>>().map_err(|_| "Blank nodes are not allowed in DELETE WHERE")?;
             Ok(vec![GraphUpdateOperation::DeleteInsert {
                 delete,