Commit 7351b73d authored by Glenn Morris's avatar Glenn Morris
Browse files

Document eager macro expansion

* doc/lispref/loading.texi (How Programs Do Loading): Add eager macro expansion.
* doc/lispref/macros.texi (Expansion): Mention eager macro expansion.

* etc/NEWS: Related edit.
parent 7f6705c3
2012-11-18 Glenn Morris <rgm@gnu.org>
* loading.texi (How Programs Do Loading): Add eager macro expansion.
* macros.texi (Expansion): Mention eager macro expansion.
2012-11-17 Glenn Morris <rgm@gnu.org>
* minibuf.texi (Basic Completion): Mention misc completion-table funcs.
......
......@@ -113,6 +113,25 @@ When loading a source file (not compiled), @code{load} performs
character set translation just as Emacs would do when visiting the file.
@xref{Coding Systems}.
@c This is referred to from the Macros chapter.
@c Not sure if it should be the other way round.
@cindex eager macro expansion
When loading an uncompiled file, Emacs tries to expand any macros
that the file contains (@pxref{Macros}). We refer to this as
@dfn{eager macro expansion}. Doing this (rather than deferring
the expansion until the relevant code runs) can significantly speed
up the execution of uncompiled code. Sometimes, this macro expansion
cannot be done, owing to a cyclic dependency. In the simplest
example of this, the file you are loading refers to a macro defined
in another file, and that file in turn requires the file you are
loading. This is generally harmless. Emacs prints a warning
(@samp{Eager macro-expansion skipped due to cycle@dots{}})
giving details of the problem, but it still loads the file, just
leaving the macro unexpanded for now. You may wish to restructure
your code so that this does not happen. Loading a compiled file does
not cause macroexpansion, because this should already have happened
during compilation. @xref{Compiling Macros}.
Messages like @samp{Loading foo...} and @samp{Loading foo...done} appear
in the echo area during loading unless @var{nomessage} is
non-@code{nil}.
......
......@@ -86,6 +86,10 @@ macro.
calls to other macros. It may even be a call to the same macro, though
this is unusual.
Note that Emacs tries to expand macros when loading an uncompiled
Lisp file. This is not always possible, but if it is, it speeds up
subsequent execution. @xref{How Programs Do Loading}.
You can see the expansion of a given macro call by calling
@code{macroexpand}.
......
......@@ -923,13 +923,13 @@ Previously, they returned NaNs on some platforms but signaled errors
on others. The affected functions are acos, asin, tan, exp, expt,
log, log10, sqrt, and mod.
** Interpreted files are eagerly macro-expanded during load.
+++
** Emacs tries to macroexpand interpreted (non-compiled) files during load.
This can significantly speed up execution of non-byte-compiled code,
but can also bump into harmless and previously unnoticed cyclic
dependencies. These should not be fatal: they will simply cause the
macro-calls to be left for later expansion (as before), but will also
result in a warning ("Eager macro-expansion skipped due to cycle")
describing the cycle.
but can also bump into previously unnoticed cyclic dependencies.
These are generally harmless: they will simply cause the macro calls
to be left for later expansion (as before), but will result in a
warning ("Eager macro-expansion skipped due to cycle") describing the cycle.
** Miscellaneous new functions:
+++
......
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