Make RelationLabel independent of map type and reduce trait bounds

crates/ir/src/lib.rs

@@ -23,7 +23,6 @@
 #![warn(missing_docs)]
 
 use std::{
-    collections::BTreeMap,
     fmt::{self, Debug},
     hash::Hash,
     str::FromStr,
@@ -52,7 +51,14 @@ use serde::{Deserialize, Serialize};
 #[derive_where(Hash; T: HashProgramInfo)]
 #[cfg_attr(feature = "serde", derive_where(Deserialize, Serialize; T: SerdeProgramInfo))]
 pub struct Program<T: ProgramInfo> {
-    pub relations: BTreeMap<T::RelationLabel, Relation<T>>,
+    /// A list of all relations defined in the program.
+    ///
+    /// The relations are identified by [ProgramInfo::RelationLabel], although
+    /// the [Program] type does not commit to using one particular structure
+    /// over another for mapping relation labels to their entries. This allows
+    /// flexibility in deferring trait bounds to when an efficient index is
+    /// actually needed.
+    pub relations: Vec<Relation<T>>,
 
     /// The list of assumptions in this program.
     pub assumptions: Vec<Assumption<T>>,
@@ -418,7 +424,7 @@ pub trait ProgramInfo {
     /// The type of relation identifiers.
     ///
     /// These labels discriminate relation entries in a [Program].
-    type RelationLabel: Ord + Info;
+    type RelationLabel: Info;
 
     /// Metadata for an assumption.
     type AssumptionMeta: Info;