Add TypeInfos.subtypes()

1 files changed, 15 insertions, 0 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeInfos.java b/src/main/java/org/shedlang/compiler/typechecker/TypeInfos.java
index 22f68b38..4547c895 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeInfos.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeInfos.java
@@ -145,6 +145,21 @@ public class TypeInfos {
         return supertypes;
     }
 
+    /**
+     * Get the subtypes of a type, from most specific to least specific.
+     */
+    public Set<Type> subtypes(Type type) {
+        var subtypes = P.orderedSet(type);
+        if (type instanceof SumType sumType) {
+            var sumTypeInfo = sumTypeInfo(sumType);
+            subtypes = subtypes.plusAll(
+                sumTypeInfo.orElseThrow().variants()
+            );
+        }
+        subtypes = subtypes.plus(Types.BOTTOM);
+        return subtypes;
+    }
+
     private Optional<SumTypeInfo> simpleSumTypeInfo(SimpleSumType type) {
         return Optional.ofNullable(sumTypeInfos.get(type));
     }