A broader analysis of this: because macros work at compile-time,
not at
runtime, you need to know the number of arguments in advance. That
means
for the case of 'and', it seems like if one had other call-by-*
semantics available in the lisp, then one wouldn't have to use a
compile-time macro?
Depends on why you're using a macro.
Calling semantics don't matter in the case of a macro. The definition
of "macro" is that it generates code prior to runtime. If you don't
know the arguments to be provided (e.g., you're using apply),
macroexpansion simply cannot occur. (You can delay macroexpansion
until runtime, but we've got a word for that: eval.)
You can sometimes avoid the use of a macro by using alternative
evaluation strategies, whether that's provided by odd calling
semantics, by pervasive laziness (e.g., one can implement `if` in
Haskell using a function), or by manual thunking (or the use of
`delay`). If that's what you mean, then the answer is "yes".
For example:
If `and` were a variadic function (defined for illustration's sake,
not efficiency):
(defn and* [& args]
(if (empty? args)
true
(and (first args)
(and* (rest args)))))
then it will evaluate all of its arguments, not short-circuit:
user=> (and* (do (println "One") false) (do (println "Two") true))
One
Two
false
Now, if we explicitly thunk our arguments, and define `and**` to un-
thunk:
(defn and** [& args]
(if (empty? args)
true
(and ((first args)) ; Changed.
(and** (rest args)))))
we get similar short-circuiting behavior to the macro version:
user=> (and** #(do (println "One") false) #(do (println "Two") true))
One
false
Does that answer your question?
-R
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