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lambda-parameters-limit

lambda-parameters-limit Constant Variable

Constant Value:

implementation-dependent, but not smaller than 50.

Description:

A positive integer that is the upper exclusive bound on the number of parameter names that can appear in a single lambda list.

See Also:

call-arguments-limit

Notes:

Implementors are encouraged to make the value of lambda-parameters-limit as large as possible.

defconstant

Expanded Reference: lambda-parameters-limit​

Inspecting the Value​

lambda-parameters-limit is an upper exclusive bound on the number of parameters that can appear in a single lambda list. The standard requires this to be at least 50.

;; Check the implementation's limit
lambda-parameters-limit
=> 1073741824

;; Guaranteed to be at least 50
(>= lambda-parameters-limit 50)
=> T

Relationship to call-arguments-limit​

lambda-parameters-limit constrains the definition side (how many parameters a function can declare), while call-arguments-limit constrains the call side (how many arguments can be passed).

;; Compare the two limits
(values lambda-parameters-limit
        call-arguments-limit)
=> 1073741824
=> 1073741824

Practical Note​

In practice, this limit is astronomically large on most implementations and you will never approach it. However, code generators or macro-writing tools that produce lambda lists programmatically should be aware of this bound.

;; Verify that a generated parameter list is within bounds
(defun check-param-count (n)
  (if (< n lambda-parameters-limit)
      (format nil "~D parameters: OK" n)
      (format nil "~D parameters: exceeds limit" n)))

(check-param-count 100)
=> "100 parameters: OK"