From 2b29af325093994cc48a6b3f6b63b04dfb5254f4 Mon Sep 17 00:00:00 2001
From: Stephen Paul Weber <singpolyma@singpolyma.net>
Date: Sun, 21 Jul 2019 21:36:24 -0500
Subject: [PATCH] List stores full type, allows for unusual annotation

---
 lib/dhall/ast.rb       | 41 ++++++++++++++++++++++++++++++++---------
 lib/dhall/binary.rb    | 12 +++++++++---
 lib/dhall/normalize.rb |  2 +-
 3 files changed, 42 insertions(+), 13 deletions(-)

diff --git a/lib/dhall/ast.rb b/lib/dhall/ast.rb
index b0444b1..745886f 100644
--- a/lib/dhall/ast.rb
+++ b/lib/dhall/ast.rb
@@ -373,9 +373,18 @@ module Dhall
 
 		include(ValueSemantics.for_attributes do
 			elements     Util::ArrayOf.new(Expression, min: 1)
-			element_type Either(nil, Expression), default: nil
+			type         Either(nil, Expression), default: nil
 		end)
 
+		def initialize(attrs)
+			if attrs.key?(:element_type)
+				et = attrs.delete(:element_type)
+				attrs[:type] = self.class.as_dhall.call(et) if et
+			end
+
+			super
+		end
+
 		def self.of(*args, type: nil)
 			if args.empty?
 				EmptyList.new(element_type: type)
@@ -388,11 +397,13 @@ module Dhall
 			Builtins[:List]
 		end
 
-		def type
-			Dhall::Application.new(
-				function: self.class.as_dhall,
-				argument: element_type
-			)
+		def element_type
+			if type.nil?
+			elsif type.is_a?(Application) && type.function == Builtins[:List]
+				type.argument
+			else
+				raise "Cannot get element_type of: #{type.inspect}"
+			end
 		end
 
 		def as_json
@@ -400,9 +411,10 @@ module Dhall
 		end
 
 		def map(type: nil, &block)
+			type = type.nil? ? nil : Builtins[:List].call(type.as_dhall)
 			with(
-				elements:     elements.each_with_index.map(&block),
-				element_type: type&.as_dhall
+				elements: elements.each_with_index.map(&block),
+				type:     type
 			)
 		end
 
@@ -450,11 +462,22 @@ module Dhall
 
 	class EmptyList < List
 		include(ValueSemantics.for_attributes do
-			element_type Either(nil, Expression)
+			type Either(nil, Expression)
 		end)
 
+		def initialize(attrs)
+			if attrs.key?(:element_type)
+				et = attrs.delete(:element_type)
+				attrs[:type] = self.class.as_dhall.call(et) if et
+			end
+
+			super
+		end
+
 		def as_json
 			[4, element_type.as_json]
+		rescue
+			[28, type.as_json]
 		end
 
 		def map(type: nil)
diff --git a/lib/dhall/binary.rb b/lib/dhall/binary.rb
index 9bdfb85..c544ce9 100644
--- a/lib/dhall/binary.rb
+++ b/lib/dhall/binary.rb
@@ -85,15 +85,21 @@ module Dhall
 
 	class List
 		def self.decode(type, *els)
-			type = type.nil? ? nil : Dhall.decode(type)
+			type = type.nil? ? nil : Builtins[:List].call(Dhall.decode(type))
 			if els.empty?
-				EmptyList.new(element_type: type)
+				EmptyList.new(type: type)
 			else
-				List.new(elements: els.map(&Dhall.method(:decode)), element_type: type)
+				List.new(elements: els.map(&Dhall.method(:decode)), type: type)
 			end
 		end
 	end
 
+	class EmptyList
+		def self.decode(type)
+			EmptyList.new(type: Dhall.decode(type))
+		end
+	end
+
 	class Optional
 		def self.decode(type, value=nil)
 			if value.nil?
diff --git a/lib/dhall/normalize.rb b/lib/dhall/normalize.rb
index 86b50c4..f5d102f 100644
--- a/lib/dhall/normalize.rb
+++ b/lib/dhall/normalize.rb
@@ -245,7 +245,7 @@ module Dhall
 
 	class EmptyList
 		def normalize
-			super.with(element_type: element_type.normalize)
+			super.with(type: type.normalize)
 		end
 	end
 
-- 
2.34.5