Implement Basic Functionalities for the Query Module

lib/rdf-model/src/lib.rs

@@ -69,9 +69,6 @@ mod traits {
 
     mod maybe_mutable;
     pub use maybe_mutable::*;
-
-    mod queryable;
-    pub use queryable::*;
 }
 pub use traits::*;
 

lib/rdf-model/src/traits/enumerable.rs

@@ -10,4 +10,7 @@ use core::error::Error;
 pub trait Enumerable:
     Countable + Iterator<Item = Result<Box<dyn Statement>, Box<dyn Error>>>
 {
+    fn grep(&self, pattern: &impl PartialEq<Box<dyn Statement>>) -> Self
+    where
+        Self: Sized;
 }

lib/rdf-query/src/graph_pattern.rs

@@ -0,0 +1,18 @@
+use crate::{pattern::Pattern, query::Query};
+
+pub enum GraphPattern {
+    BasicGraphPattern(Query),
+    TriplePattern(Pattern),
+}
+
+impl From<Query> for GraphPattern {
+    fn from(query: Query) -> Self {
+        Self::BasicGraphPattern(query)
+    }
+}
+
+impl From<Pattern> for GraphPattern {
+    fn from(pattern: Pattern) -> Self {
+        Self::TriplePattern(pattern)
+    }
+}

lib/rdf-query/src/lib.rs

@@ -6,3 +6,15 @@
 
 #![no_std]
 #![deny(unsafe_code)]
+
+pub mod graph_pattern;
+pub mod matcher;
+pub mod pattern;
+pub mod query;
+pub mod solution;
+pub mod solutions;
+pub mod variable;
+
+mod traits {
+    pub mod queryable;
+}

lib/rdf-query/src/matcher.rs

@@ -0,0 +1,56 @@
+extern crate alloc;
+
+use alloc::boxed::Box;
+use rdf_model::Term;
+
+use crate::variable::Variable;
+
+pub enum Matcher {
+    Variable(Variable),
+    Term(Box<dyn Term>),
+}
+
+impl Matcher {
+    pub fn as_variable(&self) -> Option<&Variable> {
+        match self {
+            Self::Variable(var) => Some(var),
+            _ => None,
+        }
+    }
+}
+
+impl PartialEq<&dyn Term> for Matcher {
+    fn eq(&self, term: &&dyn Term) -> bool {
+        match self {
+            Self::Variable(_) => true,
+            Self::Term(t) => t.as_str() == term.as_str(),
+        }
+    }
+}
+
+impl From<Variable> for Matcher {
+    fn from(var: Variable) -> Self {
+        Self::Variable(var)
+    }
+}
+
+impl From<&str> for Matcher {
+    fn from(name: &str) -> Self {
+        name.into()
+    }
+}
+
+impl From<Box<dyn Term>> for Matcher {
+    fn from(term: Box<dyn Term>) -> Self {
+        Self::Term(term)
+    }
+}
+
+impl core::fmt::Debug for Matcher {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        match self {
+            Self::Variable(var) => write!(f, "{:?}", var),
+            Self::Term(t) => f.write_str(&t.as_str()),
+        }
+    }
+}

lib/rdf-query/src/pattern.rs

@@ -0,0 +1,83 @@
+extern crate alloc;
+
+use alloc::{boxed::Box, collections::BTreeMap, vec};
+use rdf_model::{Statement, Term};
+
+use crate::{
+    matcher::Matcher, solution::Solution, traits::queryable::Queryable, variable::Variable,
+};
+
+pub struct Pattern {
+    subject: Matcher,
+    predicate: Matcher,
+    object: Matcher,
+    graph_name: Option<Box<dyn Term>>,
+}
+
+impl Pattern {
+    pub fn new(
+        subject: impl Into<Matcher>,
+        predicate: impl Into<Matcher>,
+        object: impl Into<Matcher>,
+        graph_name: Option<Box<dyn Term>>,
+    ) -> Self {
+        Self {
+            subject: subject.into(),
+            predicate: predicate.into(),
+            object: object.into(),
+            graph_name,
+        }
+    }
+
+    pub(crate) fn execute<Q: Queryable>(&self, queryable: &Q) -> Q
+    where
+        Self: Sized,
+    {
+        queryable.query_pattern(self)
+    }
+
+    /// Returns a query solution constructed by binding any variables in this
+    /// pattern with the corresponding terms in the given statement.
+    pub fn solution(&self, statement: Box<dyn Statement>) -> Solution {
+        let mut ans = BTreeMap::new();
+
+        let bindings = vec![
+            (self.subject.as_variable(), statement.subject()),
+            (self.predicate.as_variable(), statement.predicate()),
+            (self.object.as_variable(), statement.object()),
+        ];
+
+        for (variable, term) in bindings {
+            if let Some(variable) = variable.map(Variable::name).map(Variable::unbound) {
+                ans.insert(variable, term);
+            }
+        }
+
+        Solution::new(ans)
+    }
+}
+
+impl PartialEq<Box<dyn Statement>> for Pattern {
+    fn eq(&self, statement: &Box<dyn Statement>) -> bool {
+        let (s, p, o) = (
+            statement.subject(),
+            statement.predicate(),
+            statement.object(),
+        );
+        self.subject == s && self.predicate == p && self.object == o
+    }
+}
+
+impl core::fmt::Debug for Pattern {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        f.debug_struct("Pattern")
+            .field("subject", &self.subject)
+            .field("predicate", &self.predicate)
+            .field("object", &self.object)
+            .field(
+                "graph_name",
+                &self.graph_name.as_ref().map(|gn| gn.as_str()),
+            )
+            .finish()
+    }
+}

lib/rdf-query/src/query.rs

@@ -0,0 +1,41 @@
+extern crate alloc;
+
+use alloc::vec::Vec;
+
+use crate::{pattern::Pattern, solutions::Solutions, traits::queryable::Queryable};
+
+pub struct Query {
+    patterns: Vec<Pattern>,
+}
+
+impl Query {
+    pub fn new(patterns: Vec<Pattern>) -> Self {
+        Self { patterns }
+    }
+
+    /// Executes the query on the given graph.
+    ///
+    /// If the query nas no patterns, it returns a single empty solution as per
+    /// SPARQL 1.1 Empty Group Pattern.
+    pub fn execute<Q: Queryable>(&self, queryable: &Q) -> Solutions {
+        if self.empty() {
+            return Solutions::empty();
+        }
+
+        let solutions: Vec<_> = self
+            .patterns
+            .iter()
+            .flat_map(|pattern| {
+                let statements = pattern.execute(queryable);
+                statements.filter_map(|res| res.ok().map(|stmt| pattern.solution(stmt)))
+            })
+            .collect();
+
+        Solutions::new(solutions.into_iter())
+    }
+
+    /// Returns true if the query has no patterns.
+    pub fn empty(&self) -> bool {
+        self.patterns.is_empty()
+    }
+}

lib/rdf-query/src/solution.rs

@@ -0,0 +1,43 @@
+extern crate alloc;
+
+use alloc::collections::BTreeMap;
+use rdf_model::HeapTerm;
+
+use crate::variable::Variable;
+
+pub struct Solution {
+    bindings: BTreeMap<Variable, HeapTerm>,
+}
+
+impl Solution {
+    pub fn new(bindings: BTreeMap<Variable, impl Into<HeapTerm>>) -> Self {
+        let bindings = bindings
+            .into_iter()
+            .map(|(var, term)| (var, term.into()))
+            .collect();
+
+        Self { bindings }
+    }
+
+    pub fn binding(&self, var: &Variable) -> Option<&HeapTerm> {
+        self.bindings.get(var)
+    }
+
+    pub fn each_binding(&self) -> impl Iterator<Item = (&Variable, &HeapTerm)> {
+        self.bindings.iter()
+    }
+
+    pub fn each_name(&self) -> impl Iterator<Item = &Variable> {
+        self.bindings.keys()
+    }
+
+    pub fn each_value(&self) -> impl Iterator<Item = &HeapTerm> {
+        self.bindings.values()
+    }
+}
+
+impl core::fmt::Debug for Solution {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        f.debug_struct("Solution").finish()
+    }
+}

lib/rdf-query/src/solutions.rs

@@ -0,0 +1,37 @@
+extern crate alloc;
+
+use alloc::boxed::Box;
+
+use crate::solution::Solution;
+
+pub struct Solutions {
+    iter: Box<dyn Iterator<Item = Solution>>,
+}
+
+impl Solutions {
+    pub fn new(iter: impl Iterator<Item = Solution> + 'static) -> Self {
+        Self {
+            iter: Box::new(iter),
+        }
+    }
+
+    pub fn empty() -> Self {
+        Self {
+            iter: Box::new(core::iter::empty()),
+        }
+    }
+}
+
+impl Iterator for Solutions {
+    type Item = Solution;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next()
+    }
+}
+
+impl core::fmt::Debug for Solutions {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        f.debug_struct("Solutions").finish()
+    }
+}

lib/rdf-query/src/traits/queryable.rs

@@ -0,0 +1,33 @@
+// This is free and unencumbered software released into the public domain.
+extern crate alloc;
+
+use alloc::vec;
+use rdf_model::Enumerable;
+
+use crate::{graph_pattern::GraphPattern, pattern::Pattern, query::Query, solutions::Solutions};
+
+pub trait Queryable: Enumerable {
+    fn query(&self, pattern: impl Into<GraphPattern>) -> Solutions
+    where
+        Self: Sized,
+    {
+        match pattern.into() {
+            GraphPattern::BasicGraphPattern(query) => self.query_execute(query),
+            GraphPattern::TriplePattern(pattern) => self.query_execute(Query::new(vec![pattern])),
+        }
+    }
+
+    fn query_execute(&self, query: Query) -> Solutions
+    where
+        Self: Sized,
+    {
+        query.execute(self)
+    }
+
+    fn query_pattern(&self, pattern: &Pattern) -> Self
+    where
+        Self: Sized,
+    {
+        self.grep(pattern)
+    }
+}