Add bound expression rewrite optimizer

vortex-array/src/expr/bound_expression.rs

@@ -13,9 +13,11 @@ use vortex_error::VortexExpect;
 use vortex_error::VortexResult;
 use vortex_error::vortex_ensure;
 use vortex_session::VortexSession;
+use vortex_session::registry::CachedId;
 
 use crate::dtype::DType;
 use crate::expr::Expression;
+use crate::expr::ExpressionId;
 use crate::expr::display::DisplayTreeExpr;
 use crate::expr::scope::Scope;
 use crate::expr::traversal::TraversalOrder;
@@ -106,6 +108,17 @@ impl Hash for ExactBoundExpr {
 }
 
 impl BoundExpression {
+    /// Return the globally unique ID of this expression node implementation.
+    pub fn id(&self) -> ExpressionId {
+        match self {
+            Self::Scalar { scalar_fn, .. } => scalar_fn.id(),
+            Self::Root { .. } => {
+                static ID: CachedId = CachedId::new("vortex.expr.root");
+                *ID
+            }
+        }
+    }
+
     /// Create a bound root expression with the given dtype.
     pub fn new_root(dtype: DType) -> Self {
         Self::Root { dtype }

vortex-array/src/expr/mod.rs

@@ -44,6 +44,7 @@ use std::hash::Hasher;
 use std::sync::Arc;
 
 use vortex_error::VortexExpect;
+use vortex_session::registry::Id;
 use vortex_utils::aliases::hash_set::HashSet;
 
 use crate::dtype::FieldName;
@@ -63,6 +64,7 @@ mod exprs;
 pub(crate) mod field;
 pub mod forms;
 mod optimize;
+pub mod optimizer;
 pub mod proto;
 pub mod scope;
 pub mod stats;
@@ -120,8 +122,17 @@ pub use exprs::select_exclude;
 pub use exprs::union_child_validities;
 pub use exprs::variant_get;
 pub use exprs::zip_expr;
+pub use optimizer::BoundExpressionOptimizer;
+pub use optimizer::BoundExpressionRewriteRule;
+pub use optimizer::BoundExpressionRewriteRuleRef;
 pub use scope::*;
 
+/// A globally unique identifier for an expression node implementation.
+///
+/// Scalar-function nodes reuse their scalar-function ID. Other expression node implementations,
+/// such as higher-order functions and lambda nodes, use IDs from the same global namespace.
+pub type ExpressionId = Id;
+
 pub trait VortexExprExt {
     /// Accumulate all field references from this expression and its children in a set
     fn field_references(&self) -> HashSet<FieldName>;