hello-world values variables mutation literals constants 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 timeouts string-functions bytes command-line-arguments burstable-rate-limiting elapsed email enumerable env epoch errors exec exit file-open file-read file-write command-line-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-hashes signals sort sort-by-function spawn string-formatting tcp-client tcp-server tickers time timers urls users worker-pool line-filter