feat: add expression_evaluation.rs and add arithmetic to proof_of_sql_parser::utility (#81)

# Rationale for this change
This PR replaces #56 since we made substantial changes to evaluations in
#70, #74, #76 and #78. Please review #87 first or look at the second
commit.
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# What changes are included in this PR?
- add `PostprocessingEvaluator`
- add arithmetic to `proof_of_sql_parser::utility`
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# Are these changes tested?
Yes
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Author: iajoiner

crates/proof-of-sql-parser/src/utility.rs

@@ -53,6 +53,42 @@ pub fn or(left: Box<Expression>, right: Box<Expression>) -> Box<Expression> {
     })
 }
 
+/// Construct a new boxed `Expression` A + B
+pub fn add(left: Box<Expression>, right: Box<Expression>) -> Box<Expression> {
+    Box::new(Expression::Binary {
+        op: BinaryOperator::Add,
+        left,
+        right,
+    })
+}
+
+/// Construct a new boxed `Expression` A - B
+pub fn sub(left: Box<Expression>, right: Box<Expression>) -> Box<Expression> {
+    Box::new(Expression::Binary {
+        op: BinaryOperator::Subtract,
+        left,
+        right,
+    })
+}
+
+/// Construct a new boxed `Expression` A * B
+pub fn mul(left: Box<Expression>, right: Box<Expression>) -> Box<Expression> {
+    Box::new(Expression::Binary {
+        op: BinaryOperator::Multiply,
+        left,
+        right,
+    })
+}
+
+/// Construct a new boxed `Expression` A / B
+pub fn div(left: Box<Expression>, right: Box<Expression>) -> Box<Expression> {
+    Box::new(Expression::Binary {
+        op: BinaryOperator::Division,
+        left,
+        right,
+    })
+}
+
 /// Get table from schema and name.
 ///
 /// If the schema is `None`, the table is assumed to be in the default schema.

crates/proof-of-sql/src/base/database/expression_evaluation.rs

@@ -0,0 +1,92 @@
+use super::{ExpressionEvaluationError, ExpressionEvaluationResult};
+use crate::base::{
+    database::{OwnedColumn, OwnedTable},
+    math::decimal::{try_into_to_scalar, Precision},
+    scalar::Scalar,
+};
+use proof_of_sql_parser::{
+    intermediate_ast::{BinaryOperator, Expression, Literal, UnaryOperator},
+    Identifier,
+};
+
+impl<S: Scalar> OwnedTable<S> {
+    /// Evaluate an expression on the table.
+    pub fn evaluate(&self, expr: &Expression) -> ExpressionEvaluationResult<OwnedColumn<S>> {
+        match expr {
+            Expression::Column(identifier) => self.evaluate_column(identifier),
+            Expression::Literal(lit) => self.evaluate_literal(lit),
+            Expression::Binary { op, left, right } => self.evaluate_binary_expr(*op, left, right),
+            Expression::Unary { op, expr } => self.evaluate_unary_expr(*op, expr),
+            _ => Err(ExpressionEvaluationError::Unsupported(format!(
+                "Expression {:?} is not supported yet",
+                expr
+            ))),
+        }
+    }
+
+    fn evaluate_column(
+        &self,
+        identifier: &Identifier,
+    ) -> ExpressionEvaluationResult<OwnedColumn<S>> {
+        Ok(self
+            .inner_table()
+            .get(identifier)
+            .ok_or(ExpressionEvaluationError::ColumnNotFound(
+                identifier.to_string(),
+            ))?
+            .clone())
+    }
+
+    fn evaluate_literal(&self, lit: &Literal) -> ExpressionEvaluationResult<OwnedColumn<S>> {
+        let len = self.num_rows();
+        match lit {
+            Literal::Boolean(b) => Ok(OwnedColumn::Boolean(vec![*b; len])),
+            Literal::BigInt(i) => Ok(OwnedColumn::BigInt(vec![*i; len])),
+            Literal::Int128(i) => Ok(OwnedColumn::Int128(vec![*i; len])),
+            Literal::Decimal(d) => {
+                let scale = d.scale();
+                let precision = Precision::new(d.precision())?;
+                let scalar = try_into_to_scalar(d, precision, scale)?;
+                Ok(OwnedColumn::Decimal75(precision, scale, vec![scalar; len]))
+            }
+            Literal::VarChar(s) => Ok(OwnedColumn::VarChar(vec![s.clone(); len])),
+            Literal::Timestamp(its) => Ok(OwnedColumn::TimestampTZ(
+                its.timeunit(),
+                its.timezone(),
+                vec![its.timestamp().timestamp(); len],
+            )),
+        }
+    }
+
+    fn evaluate_unary_expr(
+        &self,
+        op: UnaryOperator,
+        expr: &Expression,
+    ) -> ExpressionEvaluationResult<OwnedColumn<S>> {
+        let column = self.evaluate(expr)?;
+        match op {
+            UnaryOperator::Not => Ok(column.element_wise_not()?),
+        }
+    }
+
+    fn evaluate_binary_expr(
+        &self,
+        op: BinaryOperator,
+        left: &Expression,
+        right: &Expression,
+    ) -> ExpressionEvaluationResult<OwnedColumn<S>> {
+        let left = self.evaluate(left)?;
+        let right = self.evaluate(right)?;
+        match op {
+            BinaryOperator::And => Ok(left.element_wise_and(&right)?),
+            BinaryOperator::Or => Ok(left.element_wise_or(&right)?),
+            BinaryOperator::Equal => Ok(left.element_wise_eq(&right)?),
+            BinaryOperator::GreaterThanOrEqual => Ok(left.element_wise_ge(&right)?),
+            BinaryOperator::LessThanOrEqual => Ok(left.element_wise_le(&right)?),
+            BinaryOperator::Add => Ok((left + right)?),
+            BinaryOperator::Subtract => Ok((left - right)?),
+            BinaryOperator::Multiply => Ok((left * right)?),
+            BinaryOperator::Division => Ok((left / right)?),
+        }
+    }
+}

crates/proof-of-sql/src/base/database/expression_evaluation_error.rs

@@ -0,0 +1,22 @@
+use crate::base::{database::ColumnOperationError, math::decimal::DecimalError};
+use thiserror::Error;
+
+/// Errors from evaluation of `Expression`s.
+#[derive(Error, Debug, PartialEq, Eq)]
+pub enum ExpressionEvaluationError {
+    /// Column not found
+    #[error("Column not found: {0}")]
+    ColumnNotFound(String),
+    /// Error in column operation
+    #[error(transparent)]
+    ColumnOperationError(#[from] ColumnOperationError),
+    /// Expression not yet supported
+    #[error("Expression {0} is not supported yet")]
+    Unsupported(String),
+    /// Error in decimal conversion
+    #[error(transparent)]
+    DecimalConversionError(#[from] DecimalError),
+}
+
+/// Result type for expression evaluation
+pub type ExpressionEvaluationResult<T> = std::result::Result<T, ExpressionEvaluationError>;