Takes a symbol naming a function, and one or more of the following: :args A regex spec for the function arguments as they were a list to be passed to apply - in this way, a single spec can handle functions with multiple arities :ret A spec for the function's return value :fn A spec of the relationship between args and ret - the value passed is {:args conformed-args :ret conformed-ret} and is expected to contain predicates that relate those values Qualifies fn-sym with resolve, or using *ns* if no resolution found. Registers an fspec in the global registry, where it can be retrieved by calling get-spec with the var or fully-qualified symbol. Once registered, function specs are included in doc, checked by instrument, tested by the runner clojure.spec.test.alpha/check, and (if a macro) used to explain errors during macroexpansion. Note that :fn specs require the presence of :args and :ret specs to conform values, and so :fn specs will be ignored if :args or :ret are missing. Returns the qualified fn-sym. For example, to register function specs for the symbol function: (s/fdef clojure.core/symbol :args (s/alt :separate (s/cat :ns string? :n string?) :str string? :sym symbol?) :ret symbol?)