a bit o' spruce, from http://play.spruce.cf

spruce.json

{"flavor":"1.29.0","prune":["meta"],"env":["HOME=/home/user"],"cherry_pick":[],"yaml":[{"filename":"file1.yml","contents":"---\nproperties:\n  system_domain: (( defer param \"What is your system domain?\" ))\n  api_url: (( defer concat \"https://api.\" properties.system_domain ))\n\n\n\n"}],"skip_eval":false,"fallback_append":false,"go_patch":false,"debug":false,"trace":false}