From 4dd9022d550eb6dcaf6c98b51c3191d032fcf356 Mon Sep 17 00:00:00 2001
From: arikheinss <arikheinss@yahoo.de>
Date: Sun, 29 Oct 2023 13:36:54 +0100
Subject: [PATCH 1/3] Make LinkedList a Union instead of Abstract type

Made Nil and Cons standalone immutable types, with LilnkedList being the Union of the two
---
 src/list.jl | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/list.jl b/src/list.jl
index fbc93b96f..9189b0d99 100644
--- a/src/list.jl
+++ b/src/list.jl
@@ -1,15 +1,16 @@
-abstract type LinkedList{T} end
 
-Base.eltype(::Type{<:LinkedList{T}}) where T = T
 
-mutable struct Nil{T} <: LinkedList{T}
-end
+struct Nil{T} end
 
-mutable struct Cons{T} <: LinkedList{T}
+struct Cons{T}
     head::T
-    tail::LinkedList{T}
+    tail::Union{Nil{T}, Cons{T}}
 end
 
+const LinkedList{T} = Union{Nil{T}, Cons{T}}
+
+Base.eltype(::Type{<:LinkedList{T}}) where T = T
+
 cons(h, t::LinkedList{T}) where {T} = Cons{T}(h, t)
 
 nil(T) = Nil{T}()

From 4e2a4378b9c5051bc742e545f0820417f72e15d1 Mon Sep 17 00:00:00 2001
From: arikheinss <arikheinss@yahoo.de>
Date: Sun, 29 Oct 2023 14:07:52 +0100
Subject: [PATCH 2/3] made == for LinkedLists iterative

---
 src/list.jl | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/list.jl b/src/list.jl
index 9189b0d99..05f23879a 100644
--- a/src/list.jl
+++ b/src/list.jl
@@ -20,7 +20,20 @@ head(x::Cons) = x.head
 tail(x::Cons) = x.tail
 
 Base.:(==)(x::Nil, y::Nil) = true
-Base.:(==)(x::Cons, y::Cons) = (x.head == y.head) && (x.tail == y.tail)
+function Base.:(==)(x::LinkedList, y::LinkedList) 
+    # can be changed to the more elegant
+    # Base.:(==)(x::Cons, y::Cons) = (x.head == y.head) && (x.tail == y.tail)
+    # once julia supports tail call recursions
+    while x  isa Cons && y isa Cons
+        x.head == y.head || return false
+        x = x.tail
+        y = y.tail
+    end
+    if x isa Cons || y isa Cons
+        return false
+    end
+    return true
+end
 
 function Base.show(io::IO, l::LinkedList{T}) where T
     if isa(l,Nil)

From d2f0813ff05f4b7af9ff07c176a38a02d36f9cd2 Mon Sep 17 00:00:00 2001
From: arikheinss <arikheinss@yahoo.de>
Date: Sun, 29 Oct 2023 14:27:31 +0100
Subject: [PATCH 3/3] added test for LinkedLists of different length

Everything for that juicy code coverage
---
 test/test_list.jl | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/test_list.jl b/test/test_list.jl
index 389d481e5..f6cbcb4a2 100644
--- a/test/test_list.jl
+++ b/test/test_list.jl
@@ -56,6 +56,7 @@
         l4 = cat(l1, l2, l3)
         @test length(l4) == 3
         @test l4 == list(1, 2, 3)
+        @test l4 ≠ list(1, 2)
         @test collect(l4) == [1; 2; 3]
         @test collect(copy(l4)) == [1; 2; 3]
         @test sprint(show,l4) == "list(1, 2, 3)"