4.1 Command-Line Parsing🔗ℹ

One small difference is that :args-in is used to specify a list of incoming arguments instead of #:argv for an incoming vector of arguments. The default :args-in uses (hash-ref (runtime-env) 'args '()). Another difference is the addition of :preamble, which supplies a string to be shown before a “usage” line, and :usage, which supplies a usage-options string as an alternative to the one inferred from an :args clause.

A more significant difference is that zuo does not have mutable data structures, so an explicit accumulator must be threaded through flag parsing. An :init clause provides the initial accumulator value defaulting to (hash). Each flag-spec either starts with an accum-id, which is bound to the value accumulated so far, or its body produces a function to receive the accumulated value; either way, the result of the body or procedure is a new accumulated value. Finally, the body of an args-clause must produce a function to receive the accumulated value.

Changed in version 1.3: Added :preamble.