Extract and test isSubType()

2 files changed, 15 insertions, 4 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index b7aafe1a..f754d0d0 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -15,6 +15,8 @@ import java.util.*;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import static org.shedlang.compiler.typechecker.TypeCheckerSubTyping.isSubType;
+
 public class TypeChecker {
 
     private TypeChecker() {
@@ -38,10 +40,6 @@ public class TypeChecker {
         return subEffect == Effects.NONE || subEffect.equals(superEffect);
     }
 
-    private static boolean isSubType(Type subType, Type superType, TypeCheckerContext context) {
-        return superType == Types.TOP || subType.equals(superType);
-    }
-
     private static Type compileTimeLookup(String name, Source source, TypeCheckerContext context) {
         var variable = context.compileTimeLookup(name)
             .orElseThrow(() -> new UnknownVariableError(name, source));
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
new file mode 100644
index 00000000..c9576191
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerSubTyping.java
@@ -0,0 +1,13 @@
+package org.shedlang.compiler.typechecker;
+
+import org.shedlang.compiler.types.Type;
+import org.shedlang.compiler.types.Types;
+
+public class TypeCheckerSubTyping {
+    private TypeCheckerSubTyping() {
+    }
+
+    static boolean isSubType(Type subType, Type superType, TypeCheckerContext context) {
+        return superType == Types.TOP || subType.equals(superType);
+    }
+}