Remove panics in EvalExpr, Evaluable, and execute_mut (#374)

Author: alancai98

CHANGELOG.md

@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 ### Changed
+- *BREAKING:* partiql-eval: `evaluate` on `Evaluable` returns a `Value` rather than an `Option<Value>`
 ### Added
+- Ability to add and view errors during evaluation with partiql-eval's `EvalContext`
 ### Fixes
 
 ## [0.4.1] - 2023-05-25

partiql-eval/src/error.rs

@@ -33,9 +33,15 @@ pub struct EvalErr {
 #[derive(Error, Debug, Clone, PartialEq, Eq, Hash)]
 #[non_exhaustive]
 pub enum EvaluationError {
+    /// Internal error that was not due to user input or API violation.
+    #[error("Illegal State: {0}")]
+    IllegalState(String),
     /// Malformed evaluation plan with graph containing cycle.
     #[error("Evaluation Error: invalid evaluation plan detected `{0}`")]
     InvalidEvaluationPlan(String),
+    /// Feature has not yet been implemented.
+    #[error("Not yet implemented: {0}")]
+    NotYetImplemented(String),
 }
 
 /// Used when an error occurs during the the logical to eval plan conversion. Allows the conversion
@@ -50,7 +56,7 @@ impl ErrorNode {
 }
 
 impl Evaluable for ErrorNode {
-    fn evaluate(&mut self, _ctx: &dyn EvalContext) -> Option<Value> {
+    fn evaluate(&mut self, _ctx: &dyn EvalContext) -> Value {
         panic!("ErrorNode will not be evaluated")
     }