From 8fcc3c851ef5bf90391920233b6f8b468e399534 Mon Sep 17 00:00:00 2001
From: Sophie Kirschner <sophie@thehumangeo.com>
Date: Mon, 20 Nov 2017 11:45:53 +0100
Subject: [PATCH] Reverse function now accepts unidrectional unknown-bounds
 inputs

Previously it would always cause an arguments error

Related to https://github.com/pineapplemachine/higher/issues/161
---
 src/core/expecting.js    | 17 +++++++++++++++++
 src/functions/reverse.js | 20 +++++++++-----------
 2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/src/core/expecting.js b/src/core/expecting.js
index 0102466..10c61b0 100644
--- a/src/core/expecting.js
+++ b/src/core/expecting.js
@@ -534,6 +534,23 @@ export const expecting = {
             return sequence;
         },
     }),
+    notUnidirectionalUnboundedSequence: Expecting({
+        type: "sequence",
+        article: "a",
+        singular: "bidirectional or not-known-unbounded sequence",
+        plural: "bidirectional or not-known-unbounded sequences",
+        adjective: "bidirectional or not-known-unbounded",
+        short: "sequence",
+        sequence: true,
+        transforms: true,
+        validate: value => {
+            const sequence = asSequence(value);
+            if(!sequence || (sequence.unbounded() && !sequence.back)){
+                throw new Error();
+            }
+            return sequence;
+        },
+    }),
     exactly: option => Expecting({
         article: "exactly",
         singular: String(option),
diff --git a/src/functions/reverse.js b/src/functions/reverse.js
index 8ef6eef..f40d977 100644
--- a/src/functions/reverse.js
+++ b/src/functions/reverse.js
@@ -120,8 +120,8 @@ export const ReverseSequence = defineSequence({
 // Implementation for reversing a known-bounded unidirectional sequence.
 export const ReverseOnDemandSequence = function(source){
     return new OnDemandSequence(ReverseSequence.appliedTo(ArraySequence), {
-        bounded: () => true,
-        unbounded: () => false,
+        bounded: () => source.bounded(),
+        unbounded: () => source.unbounded(),
         done: () => source.done(),
         back: () => source.front(),
         length: source.nativeLength ? () => source.nativeLength() : undefined,
@@ -161,15 +161,12 @@ export const reverse = wrap({
         ReverseSequence
     ],
     arguments: {
-        one: wrap.expecting.either(
-            wrap.expecting.bidirectionalSequence,
-            wrap.expecting.boundedSequence
-        ),
+        one: wrap.expecting.notUnidirectionalUnboundedSequence,
     },
     implementation: function reverse(source){
         if(source.back){
             return new ReverseSequence(source);
-        }else{ // Argument validation implies source.bounded()
+        }else{
             return ReverseOnDemandSequence(source);
         }
     },
@@ -197,14 +194,15 @@ export const reverse = wrap({
             hi.assert(seq.startsWith("olleholleholleh"));
             hi.assert(seq.endsWith("olleholleholleh"));
         },
+        "notKnownBoundedUnidirectionalInput": hi => {
+            const seq = () => hi.recur(i => i + 1).seed(1).until(i => i >= 8);
+            hi.assertEqual(seq(), [1, 2, 3, 4, 5, 6, 7]);
+            hi.assertEqual(seq().reverse(), [7, 6, 5, 4, 3, 2, 1]);
+        },
         "unboundedUnidirectionalInput": hi => {
             const seq = hi.recur(i => i + "!").seed("hello");
             hi.assertFail(() => seq.reverse());
         },
-        "notKnownBoundedUnidirectionalInput": hi => {
-            const seq = hi.recur(i => i + 1).seed(1).until(i => i >= 8);
-            hi.assertFail(() => seq.reverse());
-        },
     },
 });