|<- | <- | -> | ->| |
e : [ f cmd, input, msg: (input[0], msg)' ^ \ out 'OOPS: %s: %s' ]
– Error stream carries tuples containing (command, input, error message)
– [...] groups a sequence of commands into a single command.
– f 'cmd, input, msg: (input[0], msg) discards the command and extracts the first input.
– input and message are passed to 'OOPS: %s: %s' for formatting.