Initial Implementation

src/error.rs

@@ -0,0 +1,44 @@
+//! Error types for the optimize library.
+
+use thiserror::Error;
+
+/// The error type for TPE operations.
+#[derive(Debug, Error)]
+pub enum TpeError {
+    /// Returned when the lower bound is greater than the upper bound.
+    #[error("invalid bounds: low ({low}) must be less than or equal to high ({high})")]
+    InvalidBounds {
+        /// The lower bound value.
+        low: f64,
+        /// The upper bound value.
+        high: f64,
+    },
+
+    /// Returned when log scale is used with non-positive bounds.
+    #[error("invalid log bounds: low must be positive for log scale")]
+    InvalidLogBounds,
+
+    /// Returned when step size is not positive.
+    #[error("invalid step: step must be positive")]
+    InvalidStep,
+
+    /// Returned when categorical choices are empty.
+    #[error("categorical choices cannot be empty")]
+    EmptyChoices,
+
+    /// Returned when a parameter is suggested with a different configuration.
+    #[error("parameter conflict for '{name}': {reason}")]
+    ParameterConflict {
+        /// The name of the conflicting parameter.
+        name: String,
+        /// The reason for the conflict.
+        reason: String,
+    },
+
+    /// Returned when requesting the best trial but no trials have completed.
+    #[error("no completed trials available")]
+    NoCompletedTrials,
+}
+
+/// A specialized Result type for TPE operations.
+pub type Result<T> = std::result::Result<T, TpeError>;