case-using-failureGBBopen Toolscompiler-macroexpandccase-usingGoTo Top

ccase-using   test keyplace {clause}* => result*[Macro]

Conditionally execute the forms in a clause that is selected by matching the result of evaluating keyplace according to test, generating a correctable error if no clause is selected.

Package   :gbbopen-tools

Module   :gbbopen-tools

Arguments and values

test     A symbol designating a comparison predicate (not evaluated)
keyplace     A form; evaluated to produce a test-key and possibly also used later as a place if no keys match (see below)
results     The values returned by evaluating the last form in the selected clause

The values returned by the last form in the selected clause.

No clause was selected.

Detailed syntax

clause ::= (keys form*)


test-key     An object produced by evaluating keyplace
keys     An object or a proper list of objects.
form     A form

The specified test symbol is not evaluated; however the comparison predicate that it designates must be available during expansion of the case-using form.

The keyplace is first evaluated to produce the test-key.

Each of the clauses is then considered in turn. If the test-key matches that clause according to test, then the forms in that clause are evaluated as an implicit progn, and the values it returns are returned as the value of the ccase-using form.

If no clause is selected, a correctable error of type case-using-failure (a subclass of type-error) is signaled. The offending datum is the test-key and the expected type is type equivalent to (member (union keys :test test). Common Lisp's store-value restart can be used to correct the error.

Ccase-using is a generalization of Common Lisp's ccase macro.

See also


  > (defparameter *x* "a")
  > (ccase-using string= *x*
      ("a" 1)
      (("b" "c" "d") 2))
  > (setf *x* "d")
  > (ccase-using string= *x*
      ("a" 1)
      (("b" "c" "d") 2))
  > (setf *x* "C")
  > (ccase-using string= *x*
      ("a" 1)
      (("b" "c" "d") 2))
  Error: "C" fell through an ecase-using string= form; 
         the valid keys are "a", "b", "c", and "d".

  Restart actions (select using :c n):
    0: Supply a new value for *x*.
  >> :c 0
  Enter a form to evaluate as the new value for *x*: "a"
  *x* is now "a"

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case-using-failureGBBopen Toolscompiler-macroexpandccase-usingGoTo Top