[erlang-questions] Erlang PP Question

Kannan <>
Wed May 30 12:11:33 CEST 2012


Isn't PP takes place before parsing? Isn't PP is simply a string
replacement?



On Wed, May 30, 2012 at 3:03 PM, Richard Carlsson <
> wrote:

> On 05/30/2012 11:26 AM, Kannan wrote:
>
>> Hi There,
>>
>> If -define does just string replacement, why it does not let me do the
>> following?
>>
>> -define(Z, z() -> io:fwrite("z")).
>> -define(Y, y() -> io:fwrite("y")).
>> -define(X, ?Y. ?Z.).
>>
>
> In the last line, you have ?Y. followed by whitespace. This ends the
> define declaration. Erlang source code is divided into "forms", where each
> form ends with . followed by whitespace (usually newline, but any
> whitespace or even a comment can be used). So you have two forms at the
> end: '-define(X, ?Y.' and '?Z.).' and none of these are syntactically
> valid. It is not possible to make a single macro expand into two forms.
>
>   /Richard
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://erlang.org/pipermail/erlang-questions/attachments/20120530/f390e45a/attachment.html>


More information about the erlang-questions mailing list