Arity

MzScheme's arity procedure inspects the input arity of a procedure:

• (arity f) returns information about the number of arguments accepted by the procedure f. The result a is either:
  • an exact non-negative integer the procedure always takes exactly a arguments
  • an arity-at-least structure value the procedure takes (arity-at-least-value a) or more arguments
  • a list containing integers and arity-at-least structure values the procedure takes any number of arguments that can match one of the arities in the list
• (procedure-arity-at-least? f n returns #t if the procedure can accept n arguments (where n is an exact integer), #f otherwise.

For example:

  (arity cons) ; => 2 
  (arity list) ; => #<struct:arity-at-least> 
  (arity-at-least? (arity list)) ; => #t 
  (arity-at-least-value (arity list)) ; => 0 
  (arity-at-least-value (arity (lambda (x . y) x))) ; => 1 
  (arity (case-lambda [(x) 0] [(x y) 1])) ; => (1 2) 
  (procedure-arity-includes? cons 2) ; => #t 
  (procedure-arity-includes? display 3) ; => #f