feat: Expression system.

crates/iceberg/src/expr/bound.rs

@@ -0,0 +1,39 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! This module defines bound expressions.
+
+use crate::expr::Operator;
+use crate::spec::{Literal, NestedFieldRef};
+
+/// Bound expression.
+pub enum Bound {
+    /// Constants such as 1, 'a', true, false, null.
+    Literal(Literal),
+    /// Reference to some field in schema
+    Reference {
+        /// Nested field found in schema.
+        field: NestedFieldRef,
+    },
+    /// Expressions
+    Expr {
+        /// Operator for this expression, such as `And`, `Or`, `IsNull`, `Eq`, `LessThan`.
+        op: Operator,
+        /// Arguments for this expression. For example, `a > b` would have `a` and `b` as [`inputs`]
+        inputs: Vec<Bound>,
+    },
+}

crates/iceberg/src/expr/mod.rs

@@ -0,0 +1,49 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! This module contains expressions used in apache iceberg.
+
+mod bound;
+pub use bound::*;
+mod unbound;
+pub use unbound::*;
+
+/// Operators used in expressions.
+#[allow(missing_docs)]
+pub enum Operator {
+    IsNull,
+    NotNull,
+    IsNan,
+    NotNan,
+    LessThan,
+    LessThanOrEq,
+    GreaterThan,
+    GreaterThanOrEq,
+    Eq,
+    NotEq,
+    In,
+    NotIn,
+    Not,
+    And,
+    Or,
+    StartsWith,
+    NotStartsWith,
+    Count,
+    CountStar,
+    Max,
+    Min,
+}

crates/iceberg/src/expr/unbound.rs

@@ -0,0 +1,45 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! This module defines unbound expressions.
+
+use crate::error::Result;
+use crate::expr::bound::Bound;
+use crate::expr::Operator;
+use crate::spec::{Literal, Schema};
+
+/// Unbound expressions.
+pub enum Unbound {
+    /// Constants, such as 1, 'a', true, false, null.
+    Literal(Literal),
+    /// References to fields, such as `col` or `tbl.col`.
+    Reference(String),
+    /// Expressions
+    Expr {
+        /// Operator for this expression, such as `AND` or `OR`.
+        operator: Operator,
+        /// Arguments of this express.
+        inputs: Vec<Unbound>,
+    },
+}
+
+impl Unbound {
+    /// Bind expression to schema.
+    pub fn bind(&self, _schema: &Schema, _case_sensitive: bool) -> Result<Bound> {
+        todo!()
+    }
+}

crates/iceberg/src/lib.rs

@@ -44,5 +44,6 @@ mod avro;
 pub mod io;
 pub mod spec;
 
+pub mod expr;
 pub mod transaction;
 pub mod transform;