From bbc57bddb4dea75e3774673dbb173662e930c3dc Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Fri, 29 Dec 2023 11:22:55 +0000
Subject: Support subtyping for constructed sum types

---
 .../compiler/typechecker/TypeCheckerContext.java   | 25 ++++++++++++++++++++++
 .../compiler/typechecker/TypeCheckerSubTyping.java | 10 +++++++++
 2 files changed, 35 insertions(+)

(limited to 'src/main/java')

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java
index dcaa9226..ffd2ac01 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java
@@ -481,6 +481,31 @@ public class TypeCheckerContext {
             .orElseThrow(() -> new MissingSumTypeInfoError(type, source));
     }
 
+    public SumTypeInfo sumTypeInfo(ConstructedType<SumType> type, Source source) {
+        var typeInfo = sumTypeInfo(type.genericType(), source);
+
+        var typeSubstitutionMap = type.typeSubstitutionMap();
+
+        var variants = typeInfo.variants().stream()
+            .map(variant -> switch (variant) {
+                case SumVariant.ConstructedStruct constructedStruct ->
+                    // TODO: overload to avoid cast?
+                    SumVariant.constructedStruct((ConstructedType<StructType>) TypeSubstitution.substitute(
+                        constructedStruct.type(),
+                        typeSubstitutionMap
+                    ));
+
+                case SumVariant.Struct struct ->
+                    SumVariant.struct((StructType) TypeSubstitution.substitute(
+                        struct.type(),
+                        typeSubstitutionMap
+                    ));
+            })
+            .collect(PCollectors.toOrderedSet());
+
+        return new SumTypeInfo(variants);
+    }
+
     public TypeCheckerContext addUserDefinedEffectInfo(
         UserDefinedEffect effect,
         UserDefinedEffectInfo effectInfo
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
index 2c69ac14..4aab5370 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
@@ -28,6 +28,16 @@ public class TypeCheckerSubTyping {
                 .anyMatch(supertypeVariant -> isSubType(subtype, supertypeVariant.toType(), context));
         }
 
+        if (
+            supertype instanceof ConstructedType<?> supertypeConstructedType &&
+            supertypeConstructedType.genericType() instanceof SumType
+        ) {
+            // TODO: merge with logic for plain sum types
+            var superTypeInfo = context.sumTypeInfo((ConstructedType<SumType>) supertypeConstructedType, Sources.NULL);
+            return superTypeInfo.variants().stream()
+                .anyMatch(supertypeVariant -> isSubType(subtype, supertypeVariant.toType(), context));
+        }
+
         if (
             supertype instanceof FunctionType supertypeFunction &&
             subtype instanceof FunctionType subtypeFunction
-- 
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