Define the macro key-ifto have the form
(key-if test
:then exp1 exp2...
:else exp3 exp4...)
This does about the same thing as:
(cond test (do exp exp)
:else (do else-exp else-exp))
Almost everything is optional in key-ifexcept the test. Here are some legal forms and their
results:
user=> (key-if (> 3 1) )
nil
user=> (key-if (> 3 1) :then 'ok)
ok
user=> (key-if (< 5 3) :else 'ok)
ok
user=> (key-if (> 3 1) :else 'oops)
nil
user=> (key-if (> 3 1) :then)
nil
user=> (key-if (> 3 1) :else 'oops :then 'ok)
ok
user=> (key-if (> 3 1) :else 'oops :then (println 'hi) 'ok)
hi
ok
Note that a macro is required in order to only evaluate the relevant section. For example,
defining keyifas a function would cause launchingmissilesto be printed, as follows:
user=>(key-if (>39) :then (println 'launching-missiles)
:else 'ok)
launching-missiles
ok
This is not the desired behavior.
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