Add subtyping between sum types

1 files changed, 18 insertions, 0 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
index 4ee16c4d..4f1a283e 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
@@ -120,6 +120,24 @@ public class TypeCheckerSubTyping {
             return Optional.of(constraints);
         }
 
+        if (subtype instanceof SumType subtypeSum) {
+            var subtypeInfo = constraints.typeInfos
+                .sumTypeInfo(subtypeSum)
+                .orElseThrow();
+
+            for (var subtypeVariant : subtypeInfo.variants()) {
+                var result = tryAddSubtypeConstraint(subtypeVariant, supertype, constraints);
+                if (result.isPresent()) {
+                    // TODO: test assignment
+                    constraints = result.get();
+                } else {
+                    return result;
+                }
+            }
+
+            return Optional.of(constraints);
+        }
+
         if (supertype instanceof SumType supertypeSum) {
             var superTypeInfo = constraints.typeInfos.sumTypeInfo(supertypeSum).orElseThrow();
             return tryAddVariantSubtypeConstraint(subtype, superTypeInfo, constraints);