From 0555a22c9b7ac433b9219e25895e67da118aa3fe Mon Sep 17 00:00:00 2001
From: Stephen Paul Weber <singpolyma@singpolyma.net>
Date: Fri, 29 Mar 2019 19:57:21 -0500
Subject: [PATCH] Refactor Union typecheck

---
 lib/dhall/ast.rb       | 4 ++++
 lib/dhall/typecheck.rb | 6 ++----
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/dhall/ast.rb b/lib/dhall/ast.rb
index 0057bae..551ab6f 100644
--- a/lib/dhall/ast.rb
+++ b/lib/dhall/ast.rb
@@ -613,6 +613,10 @@ module Dhall
 			self == other
 		end
 
+		def merge(other)
+			with(alternatives: alternatives.merge(other.alternatives))
+		end
+
 		def fetch(k, default=nil)
 			if (default || block_given?) && !alternatives.key?(k)
 				return (default || yield)
diff --git a/lib/dhall/typecheck.rb b/lib/dhall/typecheck.rb
index aa1a624..0193495 100644
--- a/lib/dhall/typecheck.rb
+++ b/lib/dhall/typecheck.rb
@@ -620,10 +620,8 @@ module Dhall
 				annotated_value = @value.annotate(context)
 
 				type = Dhall::UnionType.new(
-					alternatives: { @union.tag => annotated_value.type }.merge(
-						@union.alternatives.alternatives
-					)
-				)
+					alternatives: { @union.tag => annotated_value.type }
+				).merge(@union.alternatives)
 
 				# Annotate to sanity check
 				TypeChecker.for(type).annotate(context)
-- 
2.45.2