1 files changed, 23 insertions, 2 deletions

diff --git a/subprojects/store-query/src/main/java/tools/refinery/store/query/term/DataVariable.java b/subprojects/store-query/src/main/java/tools/refinery/store/query/term/DataVariable.java
index 00950360..2206b522 100644
--- a/subprojects/store-query/src/main/java/tools/refinery/store/query/term/DataVariable.java
+++ b/subprojects/store-query/src/main/java/tools/refinery/store/query/term/DataVariable.java
@@ -6,7 +6,10 @@
 package tools.refinery.store.query.term;
 
 import org.jetbrains.annotations.Nullable;
+import tools.refinery.store.query.InvalidQueryException;
 import tools.refinery.store.query.equality.LiteralEqualityHelper;
+import tools.refinery.store.query.equality.LiteralHashCodeHelper;
+import tools.refinery.store.query.literal.EquivalenceLiteral;
 import tools.refinery.store.query.literal.Literal;
 import tools.refinery.store.query.substitution.Substitution;
 import tools.refinery.store.query.valuation.Valuation;
@@ -39,8 +42,8 @@ public final class DataVariable<T> extends AnyDataVariable implements Term<T> {
         @Override
         public <U> DataVariable<U> asDataVariable(Class<U> newType) {
                 if (!getType().equals(newType)) {
-                        throw new IllegalStateException("%s is not of type %s but of type %s".formatted(this, newType.getName(),
-                                        getType().getName()));
+                        throw new InvalidQueryException("%s is not of type %s but of type %s"
+                                        .formatted(this, newType.getName(), getType().getName()));
                 }
                 @SuppressWarnings("unchecked")
                 var result = (DataVariable<U>) this;
@@ -62,6 +65,16 @@ public final class DataVariable<T> extends AnyDataVariable implements Term<T> {
                 return other instanceof DataVariable<?> dataVariable && helper.variableEqual(this, dataVariable);
         }
 
+        @Override
+        public int hashCodeWithSubstitution(LiteralHashCodeHelper helper) {
+                return helper.getVariableHashCode(this);
+        }
+
+        @Override
+        public int hashCodeWithSubstitution(int sequenceNumber) {
+                return Objects.hash(type, sequenceNumber);
+        }
+
         public Literal assign(AssignedValue<T> value) {
                 return value.toLiteral(this);
         }
@@ -79,4 +92,12 @@ public final class DataVariable<T> extends AnyDataVariable implements Term<T> {
         public int hashCode() {
                 return Objects.hash(super.hashCode(), type);
         }
+
+        public EquivalenceLiteral isEquivalent(DataVariable<T> other) {
+                return new EquivalenceLiteral(true, this, other);
+        }
+
+        public EquivalenceLiteral notEquivalent(DataVariable<T> other) {
+                return new EquivalenceLiteral(false, this, other);
+        }
 }