From bccb3dd8f6e4d0bc7c6267f1c6b404865a14f5f2 Mon Sep 17 00:00:00 2001
From: Stephen Paul Weber <singpolyma@singpolyma.net>
Date: Sun, 31 Mar 2019 14:04:31 -0500
Subject: [PATCH] Refactor OperatorListConcatenate typecheck

---
 lib/dhall/typecheck.rb | 10 ++++------
 lib/dhall/util.rb      | 10 ++++++++++
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/lib/dhall/typecheck.rb b/lib/dhall/typecheck.rb
index a182b61..e861b7c 100644
--- a/lib/dhall/typecheck.rb
+++ b/lib/dhall/typecheck.rb
@@ -284,15 +284,13 @@ module Dhall
 				annotated_rhs = @rhs.annotate(context)
 
 				types = [annotated_lhs.type, annotated_rhs.type]
-				TypeChecker.assert types, Util::ArrayOf.new(IsList),
-				                   "Operator arguments not List: #{types}"
-
-				TypeChecker.assert annotated_lhs.type, annotated_rhs.type,
-				                   "Operator arguments do not match: #{types}"
+				assertion = Util::ArrayOf.new(Util::AllOf.new(IsList, types.first))
+				TypeChecker.assert types, assertion,
+				                   "Operator arguments wrong: #{types}"
 
 				Dhall::TypeAnnotation.new(
 					value: @expr.with(lhs: annotated_lhs, rhs: annotated_rhs),
-					type:  annotated_lhs.type
+					type:  types.first
 				)
 			end
 		end
diff --git a/lib/dhall/util.rb b/lib/dhall/util.rb
index 46e4f66..ca640f5 100644
--- a/lib/dhall/util.rb
+++ b/lib/dhall/util.rb
@@ -2,6 +2,16 @@
 
 module Dhall
 	module Util
+		class AllOf
+			def initialize(*validators)
+				@validators = validators
+			end
+
+			def ===(other)
+				@validators.all? { |v| v === other }
+			end
+		end
+
 		class ArrayOf < ValueSemantics::ArrayOf
 			def initialize(element_validator, min: 0, max: Float::INFINITY)
 				@min = min
-- 
2.38.5