cue: implement "front-style" list comprehensions

This now also allows any of the non-JSON keywords
to be used as references. Previously, these were already
supported as field names.

Issue #339
Issue #165

Change-Id: I721d054c8220ba3536f680fe2e3e502a62f99b6b
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/5683
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/doc/tutorial/kubernetes/manual/services/cloud.cue b/doc/tutorial/kubernetes/manual/services/cloud.cue
index bf86197..e16bbff 100644
--- a/doc/tutorial/kubernetes/manual/services/cloud.cue
+++ b/doc/tutorial/kubernetes/manual/services/cloud.cue
@@ -26,7 +26,7 @@
 	port: [string]: int
 
 	arg: [string]: string
-	args: [ "-\(k)=\(v)" for k, v in arg ] | [...string]
+	args: [ for k, v in arg { "-\(k)=\(v)" } ] | [...string]
 
 	// Environment variables
 	env: [string]: string