From 1d2970b3ed90e53e024a39c97f94f947e5d2d407 Mon Sep 17 00:00:00 2001
From: Takafumi Arakaki <aka.tkf@gmail.com>
Date: Sat, 9 Feb 2019 00:54:39 -0800
Subject: [PATCH 1/2] Allow @: as a macro

---
 src/julia-parser.scm | 7 ++++---
 test/syntax.jl       | 5 +++++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/julia-parser.scm b/src/julia-parser.scm
index 2a4db29d343d5..b2e8697c72f4c 100644
--- a/src/julia-parser.scm
+++ b/src/julia-parser.scm
@@ -2330,9 +2330,10 @@
                  (disallowed-space '@ nxt)))
            (with-space-sensitive
             (let ((startloc  (line-number-node s))
-                  (head (if (eq? (peek-token s) '|.|)
-                            (begin (take-token s) '__dot__)
-                            (parse-atom s #f))))
+                  (head (case (peek-token s)
+			  ((|.|) (begin (take-token s)  '__dot__))
+			  ((:) (take-token s))
+			  (else (parse-atom s #f)))))
               (peek-token s)
               (if (ts:space? s)
                   (maybe-docstring
diff --git a/test/syntax.jl b/test/syntax.jl
index bb8f5a4837636..178fb7c0fa94e 100644
--- a/test/syntax.jl
+++ b/test/syntax.jl
@@ -1832,3 +1832,8 @@ end
     allocs = @allocated identity(p)
     @test allocs == 0
 end
+
+@test Meta.parse("@: a b c") == Expr(:macrocall,
+                                     Symbol("@:"),
+				     LineNumberNode(1, :none),
+				     :a, :b, :c)

From 00f257d603810b564d0e730c3394e8db29546aa6 Mon Sep 17 00:00:00 2001
From: Takafumi Arakaki <aka.tkf@gmail.com>
Date: Fri, 15 Feb 2019 17:47:12 -0800
Subject: [PATCH 2/2] Use @: to construct a non-materialized broadcasted object

---
 base/broadcast.jl | 27 ++++++++++++++++++++++++++-
 base/exports.jl   |  1 +
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/base/broadcast.jl b/base/broadcast.jl
index 24d0424a89727..8a074511ef9e7 100644
--- a/base/broadcast.jl
+++ b/base/broadcast.jl
@@ -11,7 +11,7 @@ using .Base.Cartesian
 using .Base: Indices, OneTo, tail, to_shape, isoperator, promote_typejoin,
              _msk_end, unsafe_bitgetindex, bitcache_chunks, bitcache_size, dumpbitcache, unalias
 import .Base: copy, copyto!, axes
-export broadcast, broadcast!, BroadcastStyle, broadcast_axes, broadcastable, dotview, @__dot__
+export broadcast, broadcast!, BroadcastStyle, broadcast_axes, broadcastable, dotview, @__dot__, @:
 
 ## Computing the result's axes: deprecated name
 const broadcast_axes = axes
@@ -1211,4 +1211,29 @@ end
 end
 @inline broadcasted(::S, f, args...) where S<:BroadcastStyle = Broadcasted{S}(f, args)
 
+function _lazy end  # only used in `@:` macro; does not have to be callable
+# wrap the Broadcasted object in a tuple to avoid materializing
+@inline broadcasted(::typeof(_lazy), x) = (x,)
+
+"""
+    @: broadcasting_expression
+
+Construct a non-materialized broadcasted object from a `broadcasting_expression`
+and [`instantiate`](@ref) it.
+
+# Examples
+```jldoctest
+julia> bc = @: (1:3).^2;
+
+julia> bc isa Broadcast.Broadcasted  # it's not an `Array`
+true
+
+julia> sum(bc)  # summation without allocating an array
+14
+```
+"""
+macro (:)(ex)
+    return esc(:($instantiate(($_lazy.($ex))[1])))
+end
+
 end # module
diff --git a/base/exports.jl b/base/exports.jl
index 8a26eb8fdc73f..ee4da1e8ec10c 100644
--- a/base/exports.jl
+++ b/base/exports.jl
@@ -973,6 +973,7 @@ export
 
     @assert,
     @__dot__,
+    @:,
     @enum,
     @label,
     @goto,