7.7
cond: what it should have been
| (require cond-strict) | package: cond-strict |
This module provides cond/strict, a version of cond
that raises an error when all the clause conditions return false,
instead of returning #<void>.
syntax
(cond/strict cond-clause ...)
cond-clause = [test-expr then-body ...+] | [else then-body ...+] | [test-expr => proc-expr] | [test-expr]
Exactly like cond, except for one thing:
If there is no else clause and every test-expr returns false, cond/strict raises an error instead of returning #<void>.
Examples:
> (require cond-strict)
> (cond/strict [else 5]) 5
> (cond/strict [#false 42] [else 5]) 5
> (cond/strict [#false 42]) cond: all clause conditions were false
> (cond/strict [(positive? -5) (error "doesn't get here")] [(zero? -5) (error "doesn't get here, either")] [(positive? 5) 'here]) 'here
> (cond/strict [(member 2 '(1 2 3)) => (lambda (l) (map - l))]) '(-2 -3)
> (cond/strict [(member 2 '(1 2 3))]) '(2 3)
> (cond/strict [(member 9.75 '(1 2 3)) 42]) cond: all clause conditions were false