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Let's proceed on the interaction between active characters and macros with this small macro, which just returns its first argument:
The two pairs of quotes above are not part of the arguments of
define; rather, they are understood by the top level when it
tries to find the arguments of
define. Therefore, it is
equivalent to write:
But, while it is acceptable for a `configure.ac' to avoid unnecessary quotes, it is bad practice for Autoconf macros which must both be more robust and also advocate perfect style.
At the top level, there are only two possibilities: either you quote or you don't:
car(foo, bar, baz) =>foo [car(foo, bar, baz)] =>car(foo, bar, baz)
Let's pay attention to the special characters:
car(#) error-->EOF in argument list
The closing parenthesis is hidden in the comment; with a hypothetical quoting, the top level understood it this way:
Proper quotation, of course, fixes the problem:
The reader will easily understand the following examples:
car(foo, bar) =>foo car([foo, bar]) =>foo, bar car((foo, bar)) =>(foo, bar) car([(foo], [bar)]) =>(foo car(, ) => car([], []) =>
With this in mind, we can explore the cases where macros invoke macros....
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