I enjoy special-purpose languages and language-like markups. I have a
great deal of experience at designing, implementing, and evaluating
such things. Accordingly, there's a a lot of stuff about design
principles and pragmatics for language-like markups in my last book,
"The Art of Unix Programming".
So I've been looking at the design of WML with a critical and
analytical eye. Mostly the news is good; the language seems clean,
expressive with its domain, and well-suited to its purpose. I find
this all the more impressive since the record makes it quite clear
that the language has grown by accretion morte than by conscious
design-ahead.
However, there is one glaring exception, one thing about WML
that made me go "Bletch!" first time I saw it -- and my loathing
for it has only increased since.
That is the fact that zero-argument macro references and file
inclusions are syntactically indistinguishable -- {foo} can
mean either "call the macro 'foo'" or "include the file named
'data/foo'"; the preprocessor tries both at runtime in an order
I can't keep straight (which is a symnptom of how confusing this
design is).
Spurious messages due to macros being interpreted as filenames
(or vice-versa, it make my head hurt to try to keep track) have
been impeding our efforts to fix the filesystem port bugs.
Therefore I say let's shoot this misfeature through the head *now*.
I have support from (at least) alink, allefant, and ivanovic on this.
I propose the following new rules:
1. We implement "#include", just as in the C preprocessor and
for consistency with the existing C=like #ifdef/#else/#endif.
2. Once #include is implemented, {} is reserved for macro calls. It
will no longer bracket file inclusions under any circumstances.
3. wmllint will convert any {}-reference to a string beginning with s
lowercase letter occurring on a line by its own to an #include.
4. A call to an undefined macro will become a fatal error. An attempt
to include a file that can't be found will likewise become a fatal error.
5. To handle the mapdata="{foo.map}" case, we introduce a new tag map=
that includes map files by name reference, so the above can be
rewritten as map="foo.map".
--
<a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>
Don't ever think you know what's right for the other person.
He might start thinking he knows what's right for you.
-- Paul Williams, `Das Energi'
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