From 4f9e3f8cf89f946d71512f297626291772791e34 Mon Sep 17 00:00:00 2001
From: Jacob Quinn <quinn.jacobd@gmail.com>
Date: Fri, 24 Jun 2016 21:13:24 -0400
Subject: [PATCH] Tests and documentation for generators with guards and
 nesting.

---
 base/generator.jl  |  5 +++--
 test/functional.jl | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/base/generator.jl b/base/generator.jl
index 732aefca93903..75625c2c40525 100644
--- a/base/generator.jl
+++ b/base/generator.jl
@@ -5,8 +5,9 @@
 
 Given a function `f` and an iterator `iter`, construct an iterator that yields
 the values of `f` applied to the elements of `iter`.
-The syntax `f(x) for x in iter` is syntax for constructing an instance of this
-type.
+The syntax `f(x) [if cond(x)::Bool] for x in iter` is syntax for constructing an instance of this
+type. The `[if cond(x)::Bool]` expression is optional and acts as a "guard", effectively
+filtering out values where the condition is false.
 """
 immutable Generator{I,F}
     f::F
diff --git a/test/functional.jl b/test/functional.jl
index a266acbc04f26..56dab158f1064 100644
--- a/test/functional.jl
+++ b/test/functional.jl
@@ -435,6 +435,43 @@ let i = 1
     @test i == 1
 end
 
+# generators and guards
+
+let gen = (x for x in 1:10)
+    @test gen.iter == 1:10
+    @test gen.f(first(1:10)) == next(gen, start(gen))[1]
+    for (a,b) in zip(1:10,gen)
+        @test a == b
+    end
+end
+
+let gen = (x * y for x in 1:10, y in 1:10)
+    @test collect(gen) == collect(1:10) .* collect(1:10)'
+    @test first(gen) == 1
+    @test collect(gen)[1:10] == collect(1:10)
+end
+
+let gen = Base.Generator(+, 1:10, 1:10, 1:10)
+    @test first(gen) == 3
+    @test collect(gen) == collect(3:3:30)
+end
+
+let gen = (x for x in 1:10 if x % 2 == 0), gen2 = Filter(x->x % 2 == 0, x for x in 1:10)
+    @test collect(gen) == collect(gen2)
+    @test collect(gen) == collect(2:2:10)
+end
+
+let gen = ((x,y) for x in 1:10, y in 1:10 if x % 2 == 0 && y % 2 == 0),
+    gen2 = Filter(x->x[1] % 2 == 0 && x[2] % 2 == 0, (x,y) for x in 1:10, y in 1:10)
+    @test collect(gen) == collect(gen2)
+end
+
+# generators with nested loops (#4867)
+
+@test [(i,j) for i=1:3 for j=1:i] == [(1,1), (2,1), (2,2), (3,1), (3,2), (3,3)]
+
+@test [(i,j) for i=1:3 for j=1:i if j>1] == [(2,2), (3,2), (3,3)]
+
 # partition(c, n)
 let v = collect(Base.partition([1,2,3,4,5], 1))
     @test all(i->v[i][1] == i, v)