From 513a86423369e813dbf99bf3c90afc6f8cfb089f Mon Sep 17 00:00:00 2001
From: Stephen Paul Weber <singpolyma@singpolyma.net>
Date: Sun, 7 Apr 2019 13:54:19 -0500
Subject: [PATCH] Environment variable failure can fallback

---
 lib/dhall/ast.rb | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/lib/dhall/ast.rb b/lib/dhall/ast.rb
index 853b6ab..1f4333c 100644
--- a/lib/dhall/ast.rb
+++ b/lib/dhall/ast.rb
@@ -1075,12 +1075,16 @@ module Dhall
 			end
 
 			def resolve(resolver)
-				val = ENV.fetch(@var)
-				if val =~ /\Ahttps?:\/\//
-					URI.from_uri(URI(value))
-				else
-					Path.from_string(val)
-				end.resolve(resolver)
+				Promise.resolve(nil).then do
+					val = ENV.fetch(@var) do
+						raise ImportFailedException, "No ENV #{@var}"
+					end
+					if val =~ /\Ahttps?:\/\//
+						URI.from_uri(URI(value))
+					else
+						Path.from_string(val)
+					end.resolve(resolver)
+				end
 			end
 
 			def as_json
-- 
2.38.5