From 86180a19a7a975f1b89c726dfae3882609bb562c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bjo=CC=88rn=20Sperber?= <bjorn.sperber@soundtrap.com>
Date: Mon, 22 Jul 2019 14:31:49 +0200
Subject: [PATCH] Added asCons() and option to IList. Added head and tail to
 Cons.

---
 lib/src/ilist.dart   | 11 +++++++++++
 test/ilist_test.dart | 17 +++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/lib/src/ilist.dart b/lib/src/ilist.dart
index ecd425a..c764fae 100644
--- a/lib/src/ilist.dart
+++ b/lib/src/ilist.dart
@@ -8,6 +8,10 @@ abstract class IList<A> extends TraversableOps<IList, A> with FunctorOps<IList,
 
   Option<IList<A>> get tailOption;
 
+  Option<IList<A>> get option => asCons();
+
+  Option<Cons<A>> asCons();
+
   bool _isCons();
 
   A _unsafeHead();
@@ -357,6 +361,11 @@ class Cons<A> extends IList<A> {
   @override Option<A> get headOption => some(_head);
 
   @override Option<IList<A>> get tailOption => some(_tail);
+
+  @override Option<Cons<A>> asCons() => some(this);
+
+  A get head => _head;
+  IList<A> get tail => _tail;
 }
 
 class _Nil<A> extends IList<A> {
@@ -368,6 +377,8 @@ class _Nil<A> extends IList<A> {
   @override Option<A> get headOption => none();
 
   @override Option<IList<A>> get tailOption => none();
+
+  @override Option<Cons<A>> asCons() => none();
 }
 
 IList<A> nil<A>() => new _Nil();
diff --git a/test/ilist_test.dart b/test/ilist_test.dart
index 6ccb455..5a9aac9 100644
--- a/test/ilist_test.dart
+++ b/test/ilist_test.dart
@@ -157,4 +157,21 @@ void main() {
     }));
   });
 
+  test("to option", () {
+    qc.check(forall(intILists, (dynamicL) {
+      final l = dynamicL as IList<int>;
+      final empty = l.option.fold(() => true, (_) => false);
+      return empty == (l == nil());
+    }));
+  });
+
+  test("asCons, head and tail", () {
+    int sumThroughAsCons(IList<int> l) => l.asCons().fold(() => 0, (c) => c.head + sumThroughAsCons(c.tail));
+
+    qc.check(forall(intILists, (dynamicL) {
+      final l = dynamicL as IList<int>;
+      return sumThroughAsCons(l) == l.concatenate(IntSumMi);
+    }));
+  });
+
 }