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Source for wiki WG1BallotSnellPym version 19

author

cowan

comment

Adding #405 to Snell-Pym ballot

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98.14.173.81

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WG1BallotSnellPym

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0

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= Instructions =

    * You may list as many of the options as you want in order of preference.
    * Options are comma-delimited (ignoring space) and case-insensitive.
    * You can pipe-delimit (|) options you want to give equal weight to.
    * You may write in your own option if you announce it to the list first.
    * You may specify a variant with option/variant, for example srfi-1/module to vote for srfi-1 but clarify it should be in a separate module. Please also include the srfi-1 option in this case.
    * You can write a free-form rationale after the "preferences" line,
    * module means "yes, but I want it in a separate module",
    * wg2 means "no, but I think it should go in WG2".
    * undecided means I want to discuss this issue further.
    * Abstain on any item by leaving the preferences blank. 

= WG1 Ballot Items To Finalize By Sep. 18 =

== WG1 - Core ==

=== #121 The semantics of expt for zero bases has been refined ===

The R5RS definition of expt is:

{{{
 -- procedure: expt z1 z2
     Returns Z1 raised to the power Z2.  For z_1 ~= 0

                          z_1^z_2 = e^z_2 log z_1

     0^z is 1 if z = 0 and 0 otherwise.
}}}

however exponents with negative real parts are undefined.
R6RS attempted to clarify this with:

{{{
     0.0^z is 1.0 if z = 0.0, and 0.0 if (real-part z) is positive.
     For other cases in which the first argument is zero, either
     an error is signalled or an unspecified number is returned.
}}}

(Ignore the change in exactness, which was strictly editorial
and the examples clarify that the rules ignore exactness.)

This is unique in all the reports of a result either
signalling an error or returning a value.  The motivation
for this was because R6RS consistently removed uses of the
"is an error" terminology which would more naturally fit
this situation.

An alternative, `r5rs-error`, is to restore the "is an error"
text since we are not avoiding this in R7RS:

{{{
     0.0^z is 1.0 if z = 0.0, and 0.0 if (real-part z) is positive.
     It is an error for the first argument to be zero in other cases.

}}}

  * '''Options:''' r5rs, r5rs-error, r6rs, undecided
  * '''Default:''' r6rs
  * '''Preferences:''' r5rs-error, r5rs, r6rs
  * '''Rationale:'''  The R6RS approach isn't applicable, and I prefer explicit errors.

=== #472 clarify semantics of non-library library declarations ===

In items #91, #148 and #150 we voted to allow the
use of `include`, `include-ci` and `cond-expand`
at the "top-level" respectively, but there remains
some confusion as to their semantics.

Here "top-level" refers to repl and program body
top-levels, but not library bodies.

One interpretation is that these behave like library
declarations, and can expand into `import` forms.
In this case, for a purely static implementation of
R7RS libraries, they must first be statically scanned
from all top-level forms.  They cannot be used
outside the top-level, and are not even available
as bindings otherwise.  This is the `declaration`
proposal.

Another interpretation is that they are just normal
macros with the obvious definitions (cond-expand
in terms of the output of the `features` macro),
are available in the `(scheme base)` library, and
consequently can't be used to expand into `import`
since imports have already been resolved.  This is
the `syntax` proposal.

Alternately, we could provide `both`.  If you think
this is all too confusing you could also vote `remove`,
to drop these extensions.

  * '''Options:''' declaration, syntax, both, remove
  * '''Default:''' 
  * '''Preferences:''' declaration, syntax, both, remove
  * '''Rationale:''' "declaration" seems the simplest. "both" seems the most complex. "remove" seems to be throwing the baby out with the bathwater.


=== #473 library declaration locations in top-level ===

R6RS allows only a single library declaration, `import`,
at the beginning of a program body, and this must
contain all imported libraries.

Pending the result of ticket #472 we may also allow
`include(-ci)` and `cond-expand` to expand into
imports, and so the single form restriction would not
make sense.  However, it would be reasonable to
restrict all library declarations to the beginning of
a program - the first non-declaration would begin
the real body.  This is the `beginning-only` option.

The advantage of the `r6rs` proposal is that it would
not require any changes in existing R6RS program
loading implementations to support.  If the result of
ticket #472 indicates multiple declaration types are
available this option would automatically become
invalid, so you don't need to vote against it on those
grounds.

The advantage of the `beginning-only` option is
that it becomes possible to statically determine
all program imports without expansion, which was
the primary motivation of a static library system.

The final alternative is `any-top-level`, which
allows these forms anywhere at the top-level,
possibly interspersed with definitions.  The advantage
of this is that you can cut&paste repl sessions
(for which interspersed imports are always allowed)
as a program.  The disadvantage is that programs
can no longer be resolved separately from expansion.

  * '''Options:''' r6rs, beginning-only, any-top-level
  * '''Default:'''
  * '''Preferences:''' beginning-only, any-top-level, r6rs
  * '''Rationale:''' beginning-only is a conservative minimum to require; implementations might choose to be more flexible without becoming incompatible.

=== #405 Retract language requiring force to accept non-promises ===

#405 lumped together several issues, one of which was a requirement
(as opposed to an option) to make `force` applied to a non-promise
return its argument, as opposed to it being an error.  Thus, it would
require `(force 2) => 2`.  However, R6RS
requires `(force 2)` to signal an error, and many non-R6RS Schemes also
signal an error (see ForceNonPromise for details).  These facts were not
considered at the time.

Vote `retain` to retain this requirement, or `retract` to retract it
and leave the result of `(force 2)` implementation-dependent.

  * '''Options:''' retain, retract
  * '''Default:''' retain
  * '''Preferences:''' 

time

2012-09-25 11:34:59

version

19