Commit 11a2c8b5 by Robert Goldman

Comments with questions for Faré.

Comments so far limited to proposal 1.
parent c95698ed
......@@ -118,6 +118,12 @@ This means that if some component side-effects the `*readtable*` variable
and/or the state of the data structure it's bound to,
the effects will be seen by all components compiled with ASDF,
*including components that do not "depends-on" support functions* that the reader output produces.
<!-- I'm not sure I understand the preceding sentence. I get it -->
<!-- that this will be seen by all components compiled by ASDF, but I'm not -->
<!-- sure what "components that do not `depends-on' support function" -->
<!-- means. ASDF doesn't define what it means to depend on a function... -->
<!-- I think you have an intuitive meaning here, but I don't know what -->
<!-- it is. - RPG -->
This causes catastrophic failure, when at the REPL you e.g.
```
......@@ -198,9 +204,24 @@ either as part of the shared readtable or as part of private readtables:
4. Free software libraries will register these changes in
a suitable page of cliki.net: < http://cliki.net/Macro%20Characters >
<!-- Does the above actually protect users? -->
<!-- Even if all the libraries play by the rules, absent your -->
<!-- mechanism below ("ASDF enforces that the same readtable will be -->
<!-- used whenever building Lisp software"), if you ever accidentally -->
<!-- invoke ASDF in a context where *readtable* is rebound, the above -->
<!-- steps don't protect you, do they? IIUC, it seems like people -->
<!-- who obey the above, but don't control the readtable themselves -->
<!-- can still end up with bad outcomes, but with some cognitive -->
<!-- load. So is it worth introducing this, or should we try to -->
<!-- simply move people to controlling their readtables when needed? - RPG -->
* Optionally, declare a moratorium on defining any further such extension,
except as part of a [CDR](https://common-lisp.net/project/cdr/);
let's call that option 1.1.1 (and no such option 1.1.0).
<!-- Don't favor this declaration because I think it would just give -->
<!-- programmers a false sense of security: they might think they were -->
<!-- safer, but they have no real way of telling whether any library -->
<!-- obeys these constraints. - RPG -->
* Have ASDF itself enforce that the same readtable will be used
whenever building Lisp software, by defining a `uiop:*shared-readtable*`
......@@ -208,6 +229,15 @@ either as part of the shared readtable or as part of private readtables:
allowing developers who want to keep using the above shared modifications
and developers who prefer to use private readtables
to work without interfering with each other anymore.
<!-- I believe you mean here that the variable UIOP:*SHARED-READTABLE*
will be bound around all loading, so that users can count on it,
but it's arguably a consistent interpretation that you mean that
*READTABLE* will be bound to UIOP:*SHARED-READTABLE*. Rewrite to
clarify? Also, is this worth doing? If we fix the readtable
issue, then people need to rewrite their systems ANYWAY* to use
UIOP:*SHARED-READTABLE*: wouldnt it be better for them to go the
whole way and simply control the readtable? In which case,
UIOP:*SHARED-READTABLE* is just technical debt for ASDF.- RPG -->
* Optionally, have a similar mechanism for the `*print-pprint-dispatch*`,
for all variables modified by `with-standard-io-syntax`, and/or
......@@ -223,6 +253,12 @@ at which point changes to syntax variables can still backward-compatibly escape
from one system to the other, and it remains the responsibility of the user
to make sure that it happens in a deterministic fashion.
<!-- If this does indeed maintain backward compatibility, then it must be -->
<!-- because the "bind *READTABLE* to UIOP:*SHARED-READTABLE*" -->
<!-- interpretation of the above is correct. Right? Because if the -->
<!-- programmer has to know to use UIOP:*SHARED-READTABLE*, then we're out -->
<!-- of the territory of backward compatibility? -->
My vote is for next version of ASDF (i.e. ASAP) to implement this proposal 1,
with options 1.1.1 and 1.2.2 (and maybe later 1.2.3, if the code is ready).
......@@ -246,6 +282,10 @@ as opposed to when publishing free software libraries.
But this approach is indeed possible, and we may want to keep supporting it,
at least until we have better alternatives to offer.
<!-- Good point: since ASDF can be used to build both "composite standalone -->
<!-- systems" -- systems that consume dependencies, but are not intended to -->
<!-- be themselves depended upon -- or libraries -- systems that may or may -->
<!-- not consume dependencies, but are intended to be depended upon. -->
### Details of the proposed implementation of Proposal 1
......@@ -256,7 +296,18 @@ This readtable is presumably the
This readtable comes with all the restrictions described above.
UIOP also remembers a read-only `uiop:*standard-readtable*`
with only the standard characters.
The two above variables are not mean to be re-bound after initialization.
The two above variables are not mean to be re-bound after
initialization.
<!-- Why the use of the current value of cl:*readtable* instead of binding -->
<!-- with (copy-readtable nil)? Do we not expect -->
<!-- UIOP:*STANDARD-READTABLE* and UIOP:*INITIAL-READTABLE* to be -->
<!-- initially identical in contents (but not to be the same actual -->
<!-- object)? I take it that the initial value of `cl:*readtable*` is -->
<!-- used so that side effects happen exactly as before. If I am -->
<!-- right about this, let's document the rationale. -->
<!-- How do we go about making UIOP:*STANDARD-READTABLE* be read-only? -->
Last but not least, UIOP maintains a `uiop:*shared-readtable*`.
Its default value is `uiop:*initial-readtable*` which is backward compatible.
......@@ -275,6 +326,8 @@ a `#!` ignorer sometimes, or importantly in CCL the `#$` and `#_` readers, etc.
A strict reading of the CLHS might make this non-conformant, but
many systems might rely on it, as the ITA codebase for QRes used to.
<!-- This explains why the use of the initial readtable. -->
Systems that want to modify a persistent readtable
in ways not permitted with respect to the initial readtable
*must* arrange to use their own private readtable, e.g. via `named-readtables`.
......
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