Re: listing currently defined macros

[Eric Blake]

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According to Gary V. Vaughan on 2/17/2008 2:07 AM:

Hi Gary, and thanks for a review of my ideas, plus some cool ones of your own.

|
| However (breaking my own rule about not introducing additional macros if
| at all possible), I think list sorting and filtering are both useful enough
| idioms that we should break them out into new builtins so that our users
| needn't resort to the hackish things you mention below... which merely
| highlight deficiencys in the current language implementation.  Also,
| m4symbols proper will be faster in the case where the order of returned
| symbols is not important.  So:
|
|  -- Builtin (gnu): m4symbols([NAMES...])
|      With no arguments, `m4symbols' expands to a unordered, comma-separated
|      list of the names of all currently defined macro.  Each macro name is
|      quoted.

In other m4 implementations (I tested Solaris and OpenBSD), dumpdef output
is also unordered - it is only ordered on GNU.  But I would be okay with a
documented change to dumpdef behavior to be unordered, particularly since
we could then do:

define(`dumpdef', `builtin(`dumpdef', sort(m4symbols))')

to recover the former behavior.

|  -- Builtin (list): sort(NAME, [...])
|      Expands to a sorted, comma-separated list of quoted NAME arguments.
|      This macro was added in M4 2.0.
|

At which point, the user can easily create:

define(`cmp', `ifelse(`$1', `$2', `0',
~                      (sort(`$1', `$2')), `($1,$2)', `-1',
~                      `1')')

|
|  -- Builtin (list): uniq(NAME, [...])
|      Expands to an unordered, comma-separated list of quoted NAME
| arguments,
|      with only the first occurrence of duplicate consecutive parameters
|      listed in the expansion.  This macro was added in M4 2.0.
|
|      uniq(m4symbols(`ifndef', `ifdef', `define', `define', `ifdef',
| `undef'))
|      =>ifdef,define,ifdef

Don't you mean
~ =>ifndef,define,ifdef

|  -- Builtin (list): filter(PATTERN, LIST, [PATSYNTAX])
|      Expands to an unordered, comma-separated list of quoted LIST elements
|      that match PATTERN, either according to the current RESYNTAX (*note
|      Changeresyntax::) or PATSYNTAX if passed.
|
|      define(`dquote', ``$@'')
|      =>
|      sort(filter(`*def*', dquote(m4symbols), `GLOB'))
|      =>define,defn,dumpdef,ifdef,popdef,pushdef,undefine

Hmm.  This would be the first builtin that takes a quoted list of
elements.  Maybe it would be worth also making dquote builtin:

- -- Builtin (list): dquote(ELEMENT, ...)
~  Expand to a quoted, comma-separated list of quoted list ELEMENTs.

so that you could use dquote regardless of the current quoting characters
(in your example, it would only work with `').  Then again, dquote is easy
to implement efficiently without needing another builtin, unlike filter
(which can be implemented, but requires a foreach loop).

| I'm sure we can implement several of the m4sugar style list mangling macros
| eventually, hence I've put these new builtins into a separate list module.

Sounds like a good idea to me.  I'll see if I can get some time to write
up such a module.

|> So maybe you could argue that we already have
|> globbing if you can just translate the pattern correctly).
|
| I think this proposal has that covered.

I like the idea of using 'GLOB' as another regex syntax, although it
implies some intelligence in the underlying regex builtins (either we
would do glob->regex translation ourselves, or we would have to decide
between re_search vs. fnmatch).

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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