GBBopen 1.5 Reference -- case-using

case-using

case-using test keyform {normal-clause}* [otherwise-clause] => result* or nil [Macro]

Purpose
Conditionally execute the forms in a clause that is selected by matching the result of evaluating keyform according to test.

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 or `nil`

Returns
The values returned by the last form in the matching normal-clause; otherwise the values returned by the last form in the otherwise-clause, if specified; otherwise nil.

Detailed syntax

`normal-clause` ::=	`(keys form`*`)`
`otherwise-clause` ::=	`(`{`otherwise` \| `t`} `form`*`)`

Terms

test-key		An object produced by evaluating `keyform`
keys		An object or a proper list of objects. To refer to the symbols `t` and `otherwise` by themselves as the sole key object for a `normal-clause`, `(t)` and `(otherwise)`, respectively, must be specified as the `keys` for the clause.
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 normal-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 case-using form.

Case-using is a generalization of Common Lisp's case macro.

Examples

  > (case-using string= "a"
      ("a" 1)
      (("b" "c" "d") 2))
  1
  > (case-using string= "d"
      ("a" 1)
      (("b" "c" "d") 2))
  2
  > (case-using string= "C"
      ("a" 1)
      (("b" "c" "d") 2))
  nil
  > (case-using string= "C"
      ("a" 1)
      (("b" "c" "d") 2)
      (otherwise -1))
  -1
  > (case-using equalp "C"
      ("a" 1)
      (("b" "c" "d") 2)
      (otherwise -1))
  2
  >

The GBBopen Project

case-using