From a977e34b04fadb135bc8c209499652a777e81443 Mon Sep 17 00:00:00 2001
From: Simon Byrne <simonbyrne@gmail.com>
Date: Fri, 3 Jul 2015 10:51:33 +0100
Subject: [PATCH] Create AlephNull type for length of unbounded iterators.

---
 base/exports.jl    |  2 ++
 base/iterator.jl   | 39 ++++++++++++++++++++++++++++++++++++---
 test/functional.jl | 14 ++++++++------
 3 files changed, 46 insertions(+), 9 deletions(-)

diff --git a/base/exports.jl b/base/exports.jl
index 2971b68c4194a..78db50604ec53 100644
--- a/base/exports.jl
+++ b/base/exports.jl
@@ -28,6 +28,7 @@ export
     AbstractSparseVector,
     AbstractVector,
     AbstractVecOrMat,
+    AlephNull,
     Array,
     Associative,
     Bidiagonal,
@@ -198,6 +199,7 @@ export
     catalan,
     φ, golden,
     I,
+    ℵ₀,
 
 # Operators
     !,
diff --git a/base/iterator.jl b/base/iterator.jl
index 4fb2bcb8c34a5..75f83e5b33941 100644
--- a/base/iterator.jl
+++ b/base/iterator.jl
@@ -1,5 +1,38 @@
 # This file is a part of Julia. License is MIT: http://julialang.org/license
 
+# For unbounded length iterators
+immutable AlephNull <: Number
+end
+
+show(io::IO, ::AlephNull) = print(io, ℵ₀)
+const ℵ₀ = AlephNull()
+
+==(::Integer,::AlephNull) = false
+==(::AlephNull,::Integer) = false
+==(::AlephNull,::AlephNull) = true
+
+<(::Integer,::AlephNull) = true
+<(::AlephNull,::Integer) = false
+<(::AlephNull,::AlephNull) = false
+
+<=(::Integer,::AlephNull) = true
+<=(::AlephNull,::Integer) = false
+<=(::AlephNull,::AlephNull) = true
+
+min(x::Integer, ::AlephNull) = x
+min(::AlephNull, x::Integer) = x
+min(::AlephNull, ::AlephNull) = AlephNull()
+
+max(x::Integer, ::AlephNull) = AlephNull()
+max(::AlephNull, ::Integer) = AlephNull()
+max(::AlephNull, ::AlephNull) = AlephNull()
+
++(x::Integer, ::AlephNull) = AlephNull()
++(::AlephNull, ::Integer) = AlephNull()
++(::AlephNull, ::AlephNull) = AlephNull()
+
+-(::AlephNull, ::Integer) = AlephNull()
+
 isempty(itr) = done(itr, start(itr))
 
 # enumerate
@@ -120,7 +153,7 @@ countfrom(start::Number)               = Count(start, one(start))
 countfrom()                            = Count(1, 1)
 
 eltype{S}(it::Count{S}) = S
-length(it::Count) = Inf
+length(it::Count) = AlephNull()
 
 start(it::Count) = it.start
 next(it::Count, state) = (state, state + it.step)
@@ -184,7 +217,7 @@ end
 cycle(xs) = Cycle(xs)
 
 eltype(it::Cycle) = eltype(it.xs)
-length(it::Cycle) = Inf
+length(it::Cycle) = AlephNull()
 
 function start(it::Cycle)
     s = start(it.xs)
@@ -209,7 +242,7 @@ immutable Repeated{O}
 end
 repeated(x) = Repeated(x)
 eltype{O}(r::Repeated{O}) = O
-length(x::Repeated) = Inf
+length(x::Repeated) = AlephNull()
 
 start(it::Repeated) = nothing
 next(it::Repeated, state) = (it.x, nothing)
diff --git a/test/functional.jl b/test/functional.jl
index db7fe874204d3..ed16f7c127fc1 100644
--- a/test/functional.jl
+++ b/test/functional.jl
@@ -48,8 +48,10 @@ let b = IOBuffer("1\n2\n3\n"), a = []
         push!(a, (i,x))
     end
     @test a == [(1,"1\n"),(2,"2\n"),(3,"3\n")]
-    @test length(enumerate(eachline(b))) == 3
 end
+@test length(enumerate(1:3)) == 3
+@test length(repeated(0)) == ℵ₀
+
 
 # zip eachline (issue #7369)
 let zeb     = IOBuffer("1\n2\n3\n4\n5\n"),
@@ -83,8 +85,8 @@ let i = 0
         i <= 10 || break
     end
 end
-@test length(countfrom(0,2)) == Inf
-@test length(countfrom(0)) == Inf
+@test length(countfrom(0,2)) == ℵ₀
+@test length(countfrom(0)) == ℵ₀
 
 # take
 # ----
@@ -124,7 +126,7 @@ end
 
 @test length(drop(1:10,5)) == 5
 @test length(drop(1:10,15)) == 0
-@test length(drop(countfrom(0),5)) == Inf
+@test length(drop(countfrom(0),5)) == ℵ₀
 
 
 # cycle
@@ -138,7 +140,7 @@ let i = 0
     end
 end
 
-@test length(cycle(0:3)) == Inf
+@test length(cycle(0:3)) == ℵ₀
 
 # repeated
 # --------
@@ -158,5 +160,5 @@ let i = 0
     end
 end
 
-@test length(repeated(1)) == Inf
+@test length(repeated(1)) == ℵ₀
 @test length(repeated(1,10)) == 10