2 files changed, 14 insertions(+), 6 deletions(-)

M lib/dhall/typecheck.rb
M lib/dhall/util.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

@@ 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