hello-world values variables mutation literal constant reading-input for if-else case arrays sum range floats slices maps ok-guards nesting functions returns varadic closures recursion defer panic recover pointers new structs fields methods embedding interfaces goroutines concurrency channels buffering directions synchronization select timeout string-fns bytes command-line-args burstable-rate-limiting dns elapsed email enumerable env epoch errors exec exit file-open file-read file-write flags http-client-basic http-client http-server-basic http-server-canonical-host http-server-graceful-shutdown http-server-log http-server-middleware http-server-routing http-server-static-dynamic http-server-static-select http-server-static http-server-status-code http-server https-client https-server json number-parsing postgres rand rate-limiting redis regexs scatter-gather sha1 signals sort sortby spawn string-formatting tcp-client tcp-server tickers time timers url users worker-pool