From df10352d2eea46b3e82cbd7783ed16e3f02fced6 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Tue, 29 Mar 2016 19:30:44 +0100
Subject: Allow binding of parameterised types

---
 .../zwobble/couscous/frontends/java/JavaTypes.java | 33 +++++++++++++++++++---
 .../java/org/zwobble/couscous/util/Optionals.java  | 20 +++++++++++++
 .../tests/frontends/java/JavaTypesTests.java       | 14 +++++++++
 3 files changed, 63 insertions(+), 4 deletions(-)
 create mode 100644 src/main/java/org/zwobble/couscous/util/Optionals.java

diff --git a/src/main/java/org/zwobble/couscous/frontends/java/JavaTypes.java b/src/main/java/org/zwobble/couscous/frontends/java/JavaTypes.java
index f70ee57..a770108 100644
--- a/src/main/java/org/zwobble/couscous/frontends/java/JavaTypes.java
+++ b/src/main/java/org/zwobble/couscous/frontends/java/JavaTypes.java
@@ -2,10 +2,11 @@ package org.zwobble.couscous.frontends.java;
 
 import com.google.common.collect.ImmutableSet;
 import org.eclipse.jdt.core.dom.*;
-import org.zwobble.couscous.types.ParameterizedType;
 import org.zwobble.couscous.types.*;
+import org.zwobble.couscous.types.ParameterizedType;
 import org.zwobble.couscous.types.Type;
 import org.zwobble.couscous.types.TypeParameter;
+import org.zwobble.couscous.util.Optionals;
 
 import java.util.List;
 import java.util.Optional;
@@ -14,6 +15,7 @@ import java.util.Set;
 import static com.google.common.collect.Iterables.transform;
 import static java.util.Arrays.asList;
 import static org.zwobble.couscous.types.Types.erasure;
+import static org.zwobble.couscous.util.Casts.tryCast;
 import static org.zwobble.couscous.util.ExtraLists.eagerMap;
 
 public class JavaTypes {
@@ -84,10 +86,33 @@ public class JavaTypes {
     public static Type bind(Type genericType, Type concreteType) {
         if (genericType.equals(concreteType)) {
             return concreteType;
-        } else if (!(genericType instanceof TypeParameter)) {
-            throw new RuntimeException("Type parameter was " + genericType);
+        }
+        return Optionals.flatMap(
+            tryCast(ParameterizedType.class, genericType),
+            tryCast(ParameterizedType.class, concreteType),
+            JavaTypes::bindParameterizedType)
+            .orElseGet(() -> {
+                if (!(genericType instanceof TypeParameter)) {
+                    return concreteType;
+                } else {
+                    return new BoundTypeParameter((TypeParameter) genericType, concreteType);
+                }
+            });
+    }
+
+    private static Optional<Type> bindParameterizedType(
+        ParameterizedType genericType,
+        ParameterizedType concreteType)
+    {
+        if (genericType.getRawType().equals(concreteType.getRawType())) {
+            return Optional.of(new ParameterizedType(
+                genericType.getRawType(),
+                eagerMap(
+                    genericType.getParameters(),
+                    concreteType.getParameters(),
+                    JavaTypes::bind)));
         } else {
-            return new BoundTypeParameter((TypeParameter) genericType, concreteType);
+            return Optional.empty();
         }
     }
 }
diff --git a/src/main/java/org/zwobble/couscous/util/Optionals.java b/src/main/java/org/zwobble/couscous/util/Optionals.java
new file mode 100644
index 0000000..979dc5f
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/util/Optionals.java
@@ -0,0 +1,20 @@
+package org.zwobble.couscous.util;
+
+import java.util.Optional;
+import java.util.function.BiFunction;
+
+public class Optionals {
+    private Optionals() {}
+
+    public static <T1, T2, R> Optional<R> flatMap(
+        Optional<T1> first,
+        Optional<T2> second,
+        BiFunction<T1, T2, Optional<R>> function)
+    {
+        if (first.isPresent() && second.isPresent()) {
+            return function.apply(first.get(), second.get());
+        } else {
+            return Optional.empty();
+        }
+    }
+}
diff --git a/src/test/java/org/zwobble/couscous/tests/frontends/java/JavaTypesTests.java b/src/test/java/org/zwobble/couscous/tests/frontends/java/JavaTypesTests.java
index ae8d9c0..d450b6f 100644
--- a/src/test/java/org/zwobble/couscous/tests/frontends/java/JavaTypesTests.java
+++ b/src/test/java/org/zwobble/couscous/tests/frontends/java/JavaTypesTests.java
@@ -7,7 +7,9 @@ import org.zwobble.couscous.types.TypeParameter;
 
 import static org.junit.Assert.assertEquals;
 import static org.zwobble.couscous.types.BoundTypeParameter.boundTypeParameter;
+import static org.zwobble.couscous.types.ParameterizedType.parameterizedType;
 import static org.zwobble.couscous.types.TypeParameter.typeParameter;
+import static org.zwobble.couscous.util.ExtraLists.list;
 
 public class JavaTypesTests {
     private static final ScalarType INT_TYPE = ScalarType.of("int");
@@ -18,6 +20,7 @@ public class JavaTypesTests {
             INT_TYPE,
             JavaTypes.bind(INT_TYPE, INT_TYPE));
     }
+
     @Test
     public void bindingTypeToGenericTypeParameterReturnsBoundTypeParameter() {
         TypeParameter typeParameter = typeParameter(ScalarType.of("List"), "T");
@@ -25,4 +28,15 @@ public class JavaTypesTests {
             boundTypeParameter(typeParameter, INT_TYPE),
             JavaTypes.bind(typeParameter, INT_TYPE));
     }
+
+    @Test
+    public void bindingTypeToParameterizedTypeBindsParameters() {
+        ScalarType rawList = ScalarType.of("List");
+        TypeParameter typeParameter = typeParameter(rawList, "T");
+        assertEquals(
+            parameterizedType(rawList, list(boundTypeParameter(typeParameter, INT_TYPE))),
+            JavaTypes.bind(
+                parameterizedType(rawList, list(typeParameter)),
+                parameterizedType(rawList, list(INT_TYPE))));
+    }
 }
-- 
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