CLHS: Section 9.1.2.1

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## 9.1.2.1 Condition Designators

A number of the functions in the condition system take arguments which are identified as condition designators. By convention, those arguments are notated as

datum `&rest` arguments

Taken together, the datum and the arguments are ``designators for a condition of default type default-type.'' How the denoted condition is computed depends on the type of the datum:

* If the datum is a symbol naming a condition type ...

  The denoted condition is the result of

       (apply #'make-condition datum arguments)

* If the datum is a format control ...

  The denoted condition is the result of

       (make-condition defaulted-type
                       :format-control datum
                       :format-arguments arguments)

  where the defaulted-type is a subtype of default-type.

* If the datum is a condition ...

  The denoted condition is the datum itself. In this case, unless otherwise specified by the description of the operator in question, the arguments must be null; that is, the consequences are undefined if any arguments were supplied.

Note that the default-type gets used only in the case where the datum string is supplied. In the other situations, the resulting condition is not necessarily of type default-type.

Here are some illustrations of how different condition designators can denote equivalent condition objects:

    (let ((c (make-condition 'arithmetic-error :operator '/ :operands '(7 0))))
      (error c))
    ==  (error 'arithmetic-error :operator '/ :operands '(7 0))

    (error "Bad luck.")
    ==  (error 'simple-error :format-control "Bad luck." :format-arguments '())

The following X3J13 cleanup issue, not part of the specification, applies to this section:

- FORMAT-STRING-ARGUMENTS:SPECIFY

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