macros, procedure->macro

[Dirk Herrmann <dirk@sallust.ida.ing.tu-bs.de>]

Hi,

Guile currently supports three types of builtin macros:  "acros", "macros"
and "mmacros".  Of these, only "mmacros" work like real syntax
transformers, i. e. only "mmacros" will lead to a changed code.  Instead,
"acros" and "macros" will not change the code, but instead may even treat
their syntactic expression differently every time the same code is
encountered.

That is, if we plan to split up syntax transformation,
compilation/memoization and execution, we could not remove "acros" and
"macros" from the execution, since they may behave differently every time
the same code is executed.

I therefore strongly suggest to get rid of "acros" and "macros".  As a
first step, I suggest to get rid of "macros" and their scheme-level
representative procedure->macro: As far as I see it, there is only one use
of "macros" in guile, namely in boot-9-scm as a call to procedure->macro.  
And, to me it seems this could be replaced without problems by a call to
procedure->memoizing-macro.

I ask you for the following:

1) Some macro expert should check that replacing the call to
procedure->macro in boot-9.scm by a call to procedure->memoizing-macro is
safe.

2) Every guile user should determine, whether it would be OK if we got rid
of "macros".

3) Decide officially, whether it is OK to remove "macros" from the head
branch.

If all results are positive, I will go ahead and remove the support
for "macros" from guile.  After that, I will take a close look at "acros"
and we will play a similar game with "acros" again...

Best regards, 
Dirk Herrmann


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