| | | ecase-using | |
|
| test keyform {clause}* => result* | [Macro] |
Purpose
Conditionally execute the forms in a clause that is selected by
matching the result of evaluating keyform according to test,
generating an error if no clause is selected.
Package :gbbopen-tools
Module :gbbopen-tools
Arguments and values
| test | A symbol designating a comparison predicate (not evaluated) | |
| keyform | A form; evaluated to produce a test-key (see below) | |
| results | The values returned by evaluating the last form in the selected clause |
Returns
The values returned by the last form in the selected clause.
Errors
No clause was selected.
Detailed syntax
| clause ::= | (keys form*) |
Terms
| test-key | An object produced by evaluating keyform | |
| keys | An object or a list of objects. | |
| form | A form |
Description
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 keyform 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 ecase-using form.
If no clause is selected, a non-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).
Ecase-using is a generalization of Common Lisp's ecase macro.
See also
case-using-failure
case-using
ccase-using
Examples
> (ecase-using string= "a"
("a" 1)
(("b" "c" "d") 2))
1
> (ecase-using string= "d"
("a" 1)
(("b" "c" "d") 2))
2
> (ecase-using string= "C"
("a" 1)
(("b" "c" "d") 2))
Error: "C" fell through an ecase-using string= form;
the valid keys are "a", "b", "c", and "d".
>>
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| | | ecase-using | |