Extract inferTypeArgType()

1 files changed, 31 insertions, 26 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
index 5ff13d5b..90f3db71 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
@@ -83,32 +83,7 @@ public class TypeCheckerSubTyping {
 
             var map = this.typeBounds.keySet().stream()
                 .map(typeArg -> {
-                    var typeParamBounds = this.typeBounds.getOrDefault(typeArg, TypeBounds.EMPTY);
-
-                    var lowerBound = Types.BOTTOM;
-                    for (var lower : typeParamBounds.lower) {
-                        lowerBound = Types.commonSupertype(
-                            List.of(lowerBound, lower),
-                            this.typeInfos
-                        );
-                    }
-
-                    var upperBound = Types.TOP;
-                    for (var upper : typeParamBounds.upper) {
-                        upperBound = Types.commonSubtype(
-                            List.of(upperBound, upper),
-                            this.typeInfos
-                        );
-                    }
-
-                    if (!isSubType(lowerBound, upperBound, typeInfos)) {
-                        // TODO: proper error (or return empty and let caller throw?)
-                        throw new IllegalStateException("Incompatible type bounds");
-                    }
-
-                    var inferredType = typeParamBounds.lower.isEmpty() && !typeParamBounds.upper.isEmpty()
-                        ? upperBound
-                        : lowerBound;
+                    var inferredType = inferTypeArgType(typeArg);
 
                     return Map.<TypeLevelParam, TypeLevelValue>entry(typeArg.param(), inferredType);
                 })
@@ -116,6 +91,36 @@ public class TypeCheckerSubTyping {
 
             return new TypeSubstitutionMap(map);
         }
+
+        private Type inferTypeArgType(TypeArg typeArg) {
+            var typeParamBounds = this.typeBounds.getOrDefault(typeArg, TypeBounds.EMPTY);
+
+            var lowerBound = Types.BOTTOM;
+            for (var lower : typeParamBounds.lower) {
+                lowerBound = Types.commonSupertype(
+                    List.of(lowerBound, lower),
+                    this.typeInfos
+                );
+            }
+
+            var upperBound = Types.TOP;
+            for (var upper : typeParamBounds.upper) {
+                upperBound = Types.commonSubtype(
+                    List.of(upperBound, upper),
+                    this.typeInfos
+                );
+            }
+
+            if (!isSubType(lowerBound, upperBound, typeInfos)) {
+                // TODO: proper error (or return empty and let caller throw?)
+                throw new IllegalStateException("Incompatible type bounds");
+            }
+
+            var inferredType = typeParamBounds.lower.isEmpty() && !typeParamBounds.upper.isEmpty()
+                ? upperBound
+                : lowerBound;
+            return inferredType;
+        }
     }
 
     static Constraints addSubtypeConstraint(