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Source for wiki WG1Ballot6Gleckler version 1




Added copy of sixth ballot.







= 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 July 31 =

== WG1 - Core ==

=== #460 Semantics of `eqv?` ===

Earlier we voted on #125, #229 and #345 separately without regard to
the formal semantics of `eqv?` from a top level.  We need to first
decide what the definition of `eqv?` is, and consider if there should
be any exception cases as a secondary effect.

The debate is fundamentally one of whether we define `eqv?` in terms
of "operational equivalence" as in R6RS or a simpler rule
(e.g. resolve by `=`) as in earlier standards.

R2RS had the simplest historical rule which was simply to use `=`.

The term "operational equivalence" appears in R3RS but for numbers the
definition is the same as in R4RS and R5RS, which is `=` plus the same
exactness.  This is the `r5rs` option, with the "true" cases written formally as:

  The `eqv?` procedure returns #t if:

  (1) obj1 and obj2 are both booleans and are the same according
  to the `boolean=?` procedure.

  (2) obj1 and obj2 are both symbols and are the same symbol
  according to the `symbol=?` procedure.

  (3) obj1 and obj2 are both numbers, have the same exactness, are
  numerically equal (see `=`).

  (4) obj1 and obj2 are both characters and are the same
  character according to the `char=?` procedure.

  (5) obj1 and obj2 are both the empty list.

  (6) obj1 and obj2 are pairs, vectors, bytevectors, records,
  or strings that denote the same location in the store.

  (7) obj1 and obj2 are procedures whose location tags are equal.

Note that (7) is an exception case which will be decided
separately in #125.  Furthermore, an exception to make NaNs
unspecified regardless of the semantics here will be decided in

The `r6rs` vote replaces (3) with the following operational
equivalence semantics:

  (3.1) obj1 and obj2 are both exact numbers and are numerically
  equal (see `=`)

  (3.2) obj1 and obj2 are both inexact numbers, are numerically
  equal (see `=`), and yield the same results (in the sense of
  `eqv?`) when passed as arguments to any other procedure that
  can be defined as a finite composition of Scheme’s standard
  arithmetic procedures.

where "standard arithmetic procedures" refers arguably to either
11.7 or  For R7RS it would apply to the "Numbers"
section 6.2.6.  R6RS further adds an extra case which is not
applicable because we don't guarantee record-types are first-class

  (8) obj1 and obj2 are record-type descriptors that are
  specified to be `eqv?` in library section on “Procedural

The `r6rs/all` option changes (3.2) to a finite composition of
any of the implementations arithmetic procedures.  The intention
is that `decode-float` if provided could distinguish NaNs, but
something like `eq?` (which could distinguish the same bit
pattern in different locations) would not be considered
arithmetic and not apply.  This does leave the
definition "arithmetic" open to some interpretation.

In contrast to R6RS, R7RS does not require the full numeric tower.
This means that any definition of operational equivalence would render
many numbers unspecified from the perspective of the standard, yet
users could rely on consistency within their own implementation, and
broad agreement amongst most implementations which provide the full

Finally, the `same-bits` option replaces (3) with:

  (3.1) obj1 and obj2 are both exact numbers and are numerically
  equal (see `=`)

  (3.2) obj1 and obj2 are both inexact real numbers conforming to the
  IEEE 754-2008 standard, and they have the same radix,
  precision, maximum exponent, sign, exponent, and significand as
  described in IEEE 754-2008

  (3.3) obj1 and obj2 are both inexact real numbers, are not implemented using
  IEEE 754-2008, and are numerically equal (see `=`)

  (3.4) obj1 and obj2 are both complex numbers whose real and imaginary
  parts are `eqv?`

Keep in mind the semantics of `eqv?` also affect `memv`, `assv` and

  * '''References:'''
    * [ eqv? issues summarized]
    * [ the history of eqv? on numbers]
  * '''Options:''' r5rs, r6rs, r6rs/all, same-bits
  * '''Default:''' r5rs
  * '''Preferences:''' same-bits, r5rs, r6rs, r6rs/all

Rationale: I was impressed by Bradley's arguments that same-bits
matches IEEE 754 and is therefore superior.

The R6RS semantics are defined too indirectly and are too
dependent on the specific combination of numeric features supported by
the implementation.  The R5RS semantics are clearer.

I would argue for an option that is the same as r5rs but distinguishes
between positive and negative zero in the same way as we already
distinguish between exact and inexact, but that does not appear on the

I don't agree with choosing `r6rs/all` over `r6rs`.
Implementation-specific procedures like `decode-float`, the example
given above, are specifically designed to expose implementation
details, whereas `eqv?` has generally been used to compare numbers
arithmetically.  If we add implementation-specific procedures to the
requirement, the definition of `eqv?` becomes even more indirect, and
adding a new procedure to an implementation may change the meaning of
`eqv?` for existing code.

This whole debate illustrates the well-known futility of designing an
equivalence predicate that works for everyone's purposes.  Regardless
of the outcome of this ballot, someone who wants reliable, portable
control over exactly what numbers are considered equivalent will not
be able to use `eqv?`.

By the way, I commend the authors of this ballot item.  It has always
been, through several rewrites, well written, and the references were
particularly helpful.

=== #229 eqv? and NaN ===

As announced previously this is being re-opened due to incorrect
formulation in the previous ballot, and in response to formal comment

Regardless of the result of #460, the semantics implies that `eqv?`
return `#f` on comparing any two NaN objects.  It is reasonable to
want to consider any two NaNs as the "same" since they behave the same
under any operation, even though none of the results are `=`.  Moreover,
it is very common to use a shortcut `eq?` pointer comparison before
falling back on general `eqv?` logic.  In deference to this R6RS makes
an exception and allows the result to be unspecified, and we should
consider allowing this exception.

This proposal is only to allow an explicit exception to make
NaN comparisons unspecified, regardless of the semantics.
Vote `no-exception` (or anything other than `unspecified`)
to require NaN comparisons to follow directly from #460.

The default of `unspecified` still holds from the previous invalidated

  * '''Options:''' no-exception, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' unspecified

Rationale: There is not enough agreement about this to make a
requirement.  NaN's can be addressed specially by code that uses them.

=== #125 Allow procedures not to be locations (making EQV? unspecified in some additional cases) ===

Procedures are another case for contention with `eqv?`.  In R3RS, an
operational equivalence was defined for procedures, and this was
subsequently removed.

R6RS went the other direction and allowed the exact same procedure `x`
to return `#f` for `(eqv? x x)`, and R7RS currently reaffirms this.
The rationale behind this is for compiler optimizations such as
inlining local procedures, that is given:

(let ((square (lambda (x) (* x x))))
  (eqv? square square))

it is reasonable for a compiler to perform the optimization:

(eqv? (lambda (x) (* x x)) (lambda (x) (* x x)))

in which case the result would naturally return `#f`.

Vote `yes` to allow the result to be `#f`.

The default of `yes` still holds from the previous invalidated ballot.

  * '''Options:''' yes, no, undecided
  * '''Default:''' yes
  * '''Preferences:''' no

Rationale: Absolutely not.  This would mean that even `eq?` wouldn't
work after such an optimization.

=== #393 Defining record equality ===

Currently, R7RS-small says that when `equal?` is applied to records
that are not `eqv?` (that were constructed by different calls to the
record constructor), the result may be `#t` or `#f` at the
implementation's discretion.  The proposal is to treat records of the same
type like pairs, strings, vectors, and bytevectors: that is, their
contents are recursively compared.

Vote `recursive` to require recursive comparison of the record's
fields, `identity` to return `#t` iff `eqv?` does, and `unspecified`
to leave this open.

Note `equal?` is already required to handle cycles regardless.

  * '''Options:''' recursive, identity, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' recursive

Rationale: This is merely making `equal?` on records consistent with
`equal?` on other data types.

=== #306 What does "full Unicode" support mean in Appendix B? ===

Specifically, does it indicate case-folding and normalization support
for the repertoire of any particular version of Unicode, or any
version greater than 5 or 6 or 6.1, or no particular version?

Full unicode refers to the set of characters available.  Case-folding
and character predicates are required to work according to the Unicode
standard for all supported characters.  The question of which version
of Unicode the property refers to is important.  We could require a
specific version (and all further revisions), or always require the
latest official Unicode standard, in which case an implementation
would not be compliant until it was updated with each new standard.  Alternatively, we could parameterize the feature identifier, so that implementations might claim to support (full-unicode 6), (full-unicode 6.1), etc.

  * '''Options:''' at-least-6, at-least-6.1, latest, parameterize, undecided, unspecified
  * '''Default:''' unspecified
  * '''Preferences:''' at-least-6, at-least-6.1, unspecified

Rationale: Specifying `latest` is unrealistic.  That would mean that
existing Scheme implementations would fall out of compliance the
moment a new Unicode standard was promulgated.  Specifying a point
version, e.g. 6.1, is also unrealistic, as the version of Unicode that
a particular implementation is reasonably able to support depends so
much on underlying facilities provided, for example, by the operating

=== #458 Remove the formal semantics from the report ===

There have been a bunch of complaints about the formal semantics: it's
incomplete, it cannot be mechanized with a proof assistant, it doesn't
help either users or implementers very much, and so on.  See in
particular #453.

The semantics have been updated to include `dynamic-wind`, however the
other arguments still hold.

This proposal is to remove it from the report altogether, and to urge
the Steering Committee to create a new WG to produce one, likely in a
"rolling" style with increasingly comprehensive releases, on its own
schedule.  Some members of the current WG have expressed interest in
serving on such a group, and others have expressed their complete lack
of interest, so a new WG seems the best choice if this is done.

Alternately, we can adapt the operational semantics from R6RS.

  * '''Options:''' remove, keep, operational, undecided
  * '''Default:''' keep
  * '''Preferences:''' keep, remove

Rationale: I've never understood the fascination with formal
semantics, particularly considering that they're non-normative,
i.e. that the English has always taken precedence.  We always get the
English right, then adjust the formal semantics to match.  In all my
years of using the RnRS specifications for reference, I have not once
referred to the formal semantics in order to understand some point of
the language.

Nevertheless, the formal semantics do matter a lot to many people in
the community.  Removing them, even temporarily, will probably cause
us to lose support for the draft.  I'm afraid that we're going to have
to find a way -- some volunteers? -- to bring that part of the
document up to date.

There's no point in adopting the operational semantics from R6RS since
it's not compatible with R7RS.

=== #398 Allow repeated keys in `case` ===

R5RS says it's an error for a key to appear in more than one clause of
`case` (or twice in the same clause, but that's trivial).  R6RS allows
the same key to appear more than one clause, but insists on
left-to-right testing throughout, like `cond`.  The R6RS editors
thought this was better for machine-generated code, though worse for
hand-written code.

The proposal is a compromise: allow keys to appear in more than one clause,
but behave as if the key appeared only in the first (leftmost) clause.
This allows hash-table or other non-left-to-right implementations.

  * '''Options:''' r5rs, r6rs, leftmost, unspecified, undecided
  * '''Default:''' r5rs
  * '''Preferences:''' leftmost, r6rs

Rationale: The argument from machine-generated code, e.g. macros,
makes perfect sense, but the `leftmost` proposal gives implementations
more freedom to achieve the same ends.

=== #85 Blobs, bytevectors, byte-vectors, octet-vectors, or something else?

Following exactly in the footsteps of R6RS we voted for a `blob` API
and then changed the name to `bytevector`.

Formal comment #435 argues that `u8vector` is in more common use, so
this item is being re-opened.  The default is the current draft
`bytevector`, and for any member leaving the preferences are left
blank their votes from ballot 3 will be used.

  * '''Options:''' blob, bytevector, byte-vector, u8vector, octet-vector, undecided
  * '''Default:''' bytevector
  * '''Preferences:''' byte-vector, bytevector, u8vector, octet-vector, blob

Rationale: While "blob" is a widely used term these days, I prefer a
properly hyphenated, descriptive term, or at least a descriptive term.
I've never liked "blob," even knowing that it abbreviates "Binary
Large OBject."  Since R7RS is case sensitive, we don't need even more
cases where the capitalization of an abbreviation is not matched in
the names of Scheme identifiers.  Furthermore, it has been ages since
"byte" meant anything other than eight bits, so there's no need to
choose "u8" or "octet."

While Marc's argument that we (and implementers of the widely adopted
SRFI 4) use "#u8(" to prefix literal byte vectors is compelling, the
idea of byte vectors is to provide the basis for a more complete
system in WG2 Scheme that supports reading and writing not only
unsigned bytes, but also other data types, e.g. IEEE floats, and mixed
types as well.  It's useful to distinguish this idea by name even if
the underlying data type is the same.

== WG1 - Library System ==

=== #353 No use before import in libraries ===

For ease of implementation, the proposal is to make it an error for an
imported identifier to be referenced or defined in a library before
the library declaration that imports it.  This allows strict
left-to-right processing of library declarations, with no need to
delay processing till the end of the library.

Therefore, this would be an error (but still permitted as an extension
in Schemes that can easily provide it):

  (begin (define x y))
  (import (library defining y))

This would necessitate replacing the penultimate paragraph of section
5.5.1 with:

One possible implementation of libraries is as follows: After all
`cond-expand` library declarations are expanded, a new environment is
constructed for the library consisting of all imported bindings. The
expressions and declarations from all `begin`, `include`, and
`include-ci` declarations are expanded in that environment in the
order in which they occur in the library declaration.  Alternatively,
`cond-expand` and `import` declarations may be processed in left to
right order interspersed with the processing of expressions and
declarations, with the environment growing as imported bindings are
added to it by each `import` declaration.

Vote `yes` to add the restriction, or `no` to leave it out.

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: I'm not sure why we even allow `begin`, `include`, or
`include-ci` before any `import` or `export` form.  The proposed
restriction is not limiting, and simplifies not only implementing the
library system, but also reading code that uses it.

=== #359 Limit numbers used in library names ===

This is a proposal to limit numbers in library names to the range 0 to
32767.  Currently, there is no portable lower bound which all Schemes
can assume as the maximum size of an integer.

Numbers are mostly used for SRFI-based libraries anyway, which are not
likely to reach either limit.

The option `uint15` for the proposal as stated (0 to 32767), `int16`
for -32768 to 32767, int24 for -2^23^ to 2^23^-1, etc.

Vote `unspecified` to make no explicit requirement on the integers
allowed in library names.

  * '''Options:''' uint15, int16, uint16, int24, uint24, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' int16, uint16, unspecified, int24, uint24

Rationale (from my earlier ballot on #349): Twenty-four is too many
bits to require for tiny implementations.  I'm nervous about burdening
the smallest implementations with even a sixteen-bit requirement, but
such implementations typically already leave out significant language
features, so I'm willing to ask for 16 bits.

=== #441 Make sure a program/library loads any imported libraries at most once ===

Add the following text to the discussion of library loading:

 Regardless of the number of times that a library is loaded, each
 program or library that imports bindings from a library will receive
 bindings from a single loading of that library, regardless of the
 number of `import` or `cond-expand` declarations in which it appears.

to make it clear that, for example,

(import (prefix (foo) 'foo:))
(import (only (foo) bar))

will cause `bar` and `foo:bar` to come from the same instantiation of
the library '(foo)'

Vote `yes` to add this requirement.

  * '''Options:''' yes, no, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' yes, unspecified

Rationale: Yes, we don't want people to interpret `import` as a
statement causing an import to happen rather than a declaration that
one should.  However, the wording still isn't clear, and in fact seems
to suggest the opposite of its intent.  I recommend this instead:

 Regardless of the number of times that a library is loaded, all the
 bindings it exports to any loading program or library will come from
 a single loading of that library, regardless of the number of
 `import` or `cond-expand` declarations in which it appears.

=== #402 Add an export-all form. ===

Add an export-all form to the library declaration that means "export
all identifiers that are defined in the library with begin, include,
and include-ci but none that are imported with import."

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: This will be a common usage pattern.  It's much better than
the alternative suggestion, which was to make all identifiers be
exported if none are.  That violates the principle of least

I don't understand Alex's argument that this will be hard to
implement.  If something like that is hard, we're doing something

=== #448 Add library declaration include-library-declarations ===

The proposed `include-library-declarations` allows a library to
incorporate a file containing arbitrary library declarations, not just
Scheme code (definitions and expressions).  This allows, for example,
the exports of a module to be written directly in the library file,
and its imports in a separate file.

An alternative would be something like `(export-from <library>)` to
export the same bindings as another library.  This does require the
clumsiness of actually defining the identifiers in the other library
if it is abstract.

  * '''Options:''' include-library-declarations, export-from, no, undecided
  * '''Default:''' no
  * '''Preferences:''' no

Rationale: I don't understand why writing the imports in a separate
file is a good idea.  I view the imports and exports as part of a
"wiring diagram" showing how parts of the system are connected, not a
way of declaring an abstract interface.  In any case, this is
invention, not something that exists in Scheme implementations
already, so it doesn't belong in the standard.

=== #449 Clarify library loading rules ===

R7RS currently says:

 Within a program, each imported library is loaded at least once, and,
 if imported by more than one program or library, may possibly be
 loaded additional times.

Richard Kelsey thinks this is too liberal, and proposes:

 Regardless of the number of times that a library is loaded, each
 program or library that imports bindings from a library will receive
 bindings from a single loading of that library, regardless of the
 number of `import` or `cond-expand` forms in which it appears.

Aaron Hsu, however, thinks this is too restrictive, and proposes
(backed up by actual R6RS implementations):

 If a library's definitions are referenced in the expanded form of a
 program or library body, then that library must be loaded before the
 expanded program or library body is evaluated. This rule applies

 Similarly, during the expansion of a library, if a syntax keyword
 imported from a library is needed to expand the library, then the
 imported library must be visited before the expansion of the
 importing library.

  * '''Proposals:'''
    * '''one:''' Kelsey's proposal
    * '''one-or-more:''' current draft
    * '''zero-or-more:''' Hsu's proposal, R6RS status-quo
    * '''zero-or-one:''' Kelsey's proposal with Hsu's relaxation
  * '''Options:''' one, one-or-more, zero-or-one, zero-or-more
  * '''Default:''' one-or-more
  * '''Preferences:''' one, zero-or-one, one-or-more, zero-or-more

Rationale: Our library system is designed to have simple semantics,
and divergence from once-and-only-once makes it harder to reason
about.  If we are going to do something else, let's still make sure
that modules aren't loaded more than once.

== WG1 - Numerics ==

=== #366 Add (log z b) for logarithm of z to the base b ===

Coverage for this R6RS feature is currently sparse: only Gauche, Chez,
Vicare, Larceny, Ypsilon, Mosh, !IronScheme, KSi, RScheme, Rep support
it.  But it is convenient when working in bases other than ''e'' such
as 10, 2, or 16, and it is just a few extra lines of code, since `(log
z b)` => `(/ (log z) (log b))` for arbitrary complex numbers ''z, b''.

Vote `yes` to add the optional second argument from R6RS.

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: This is simple, widely useful, and conforms to R6RS.

=== #367 Inexact division by exact zero ===

Draft 6 says that it's an error for an argument of `/` (other than the
first) to be an exact zero.  R6RS, however, says that it's an error
only if ''all'' the arguments are exact.  In other words, `(/ 2.0 0)`
is an error according to the draft, but in R6RS it returns `+inf.0`
(assuming the implementation supports it).  The proposal is to adopt
the R6RS wording.

Cowan tested `(/ 2.0 0)` in the usual set of Schemes:

 * Racket, Gambit, Chicken (with the numbers egg), Guile, Chibi, Elk, Spark report an error.
 * Gauche, Bigloo, Scheme48/scsh, Kawa, SISC, Chez, SCM, !Ikarus/Vicare, Larceny, Ypsilon, Mosh, !IronScheme, NexJ, STklos, RScheme, BDC, UMB, VX return `+inf.0`.
 * MIT, scsh, Shoe, !TinyScheme, Scheme 7, XLisp, Rep, Schemik, Inlab always report an error when dividing by zero, exact or inexact.
 * KSi, Scheme 9 produce incorrect results.
 * !SigScheme, Dream, Oaklisp, Owl Lisp don't support inexact numbers.

Vote `error` for the current draft semantics that it is an error,
`all-error` for the R6RS semantics that it is only an error if all
arguments are exact, or `unspecified` to make this case unspecified.

  * '''Options:''' error, all-error, unspecified, undecided
  * '''Default:''' error
  * '''Preferences:''' error, all-error

Rationale: Division by zero is still typically a mistake, and catching
it as early as possible is a good idea.  Until we specify how an
implementation goes into IEEE non-signalling mode, we should continue
signalling such errors.

=== #369 Require that - and / allow an arbitrary number of arguments ===

R5RS requires that `-` and `/` accept one or two arguments, and labels
support for more than two as "optional".  R6RS requires such support.
The proposal is to require it.

All Schemes in the test suite support more than two arguments except
Scheme48/scsh.  (Owl Lisp does not support variadic procedures of any

Vote `require` for required n-ary behavior and `optional` to leave it
optional as in R5RS.  Alternately, vote `forbidden` to make this
always an error in all implementations.

  * '''Options:''' required, optional, forbidden, undecided
  * '''Default:''' optional
  * '''Preferences:''' required, optional

Rationale: It's not hard to make this just work, and almost all
Schemes already support it.

=== #370 Log of exact and inexact zero ===

R5RS and draft 6 of R7RS don't say what `(log 0.0)` and `(log 0)`
return.  R6RS requires `-inf.0` and an exception respectively.  The
proposal is to say that `(log 0.0)` returns `-inf.0` on systems that
have `-inf.0`, and that `(log 0)` is an error.

In Racket, Gambit, Chicken (with the numbers egg), Guile, Chibi, Chez,
!Ikarus/Vicare, Larceny, Ypsilon, Mosh, !IronScheme, STklos, Spark,
`(log 0.0)` returns `-inf.0` and `(log 0)` raises an exception.

Gauche, MIT, Chicken (without the numbers egg), Bigloo, Scheme48/scsh,
Kawa, SISC, SCM, NexJ, KSi, RScheme, XLisp, Rep, VX, SXM, Inlab return
`-inf.0` in both cases.

Elk, UMB, Oaklisp raise an exception in both cases.

Scheme 7 returns the wrong answer in both cases.

!SigScheme, Shoe, !TinyScheme, Dream, BDC, Owl Lisp don't support `log`.

Scheme 9 apparently goes into an infinite loop in both cases.

Vote `r6rs` for the R6RS behavior of returning `-inf.0` and raising an
error, respectively.  Vote `infinity` to always return `-inf.0`.

  * '''Options:''' r6rs, infinity, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' r6rs, unspecified

Rationale: Let's catch errors early.

=== #407 Dividing exact 0 by an inexact number ===

This proposal allows `(/ 0 `''x''`)`, where ''x'' is an inexact
number, to return an exact value.  Currently only Racket, Gambit,
!TinyScheme, Sizzle, Spark do this; see [wiki:Zero Zero] for details.

Vote `zero` to allow (but not require) this to return exact 0.  Vote
`no-nan` to allow it to return 0 except when `x` is `+nan.0`, where it
would return `+nan.0`.

  * '''Options:''' zero, no-nan, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' no-nan, zero, unspecified

Rationale: Zero divided by anything is zero.  We know the answer
exactly given only an exact numerator, so we should return an exact
answer.  However, as John points out, a NaN may indicate an earlier
error, and we shouldn't require masking that.

=== #410 Infinity vs. NaN in max and min ===

Currently R7RS says nothing about the value of `(max +inf.0 +nan.0)`
or `(min -inf.0 +nan.0)`.  R6RS required these functions to return the
infinite value, but this was adopted by some but not all R6RS
implementations (see MaxInfNan for details).  R5RS implementations are
also divided.

The proposal is to allow R7RS implementations to provide either value.

Vote `both` to explicitly add a note that either are allowed,
`infinity` to require the infinite value as in R6RS, `nan` to require
returning `+nan.0`, and `unspecified` leave unspecified (i.e. the same
as `both` but without the note).

  * '''Options:''' both, infinity, nan, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' both, unspecified, nan, infinity

Rationale: I'm changing this for the same reason I changed my answer
to #407, i.e. because a NAN may indicate an earlier error and we
shouldn't lose the information that there was an error.

=== #395 Infinite and NaN complex numbers ===

Currently both `infinite?` and `nan?` return `#t` to a complex number
like `+inf.0+nan.0i`.  Is this the Right Thing, or should `infinite?`
only return `#t` if neither part is a NaN?

Note it is reasonable for an implementation to not support partial nan
complex numbers.

Vote `disjoint` to ensure that `infinite?` and `nan?` are disjoint
predicates as in the proposal, or `overlap` to allow the current

  * '''Options:''' overlap, disjoint, unspecified, undecided
  * '''Default:''' overlap
  * '''Preferences:''' overlap, disjoint

Rationale: I'm not sure how useful it is to ask whether a complex
number is infinite, but the only reasonable interpretation I can see
is that if either part is infinite, the complex number is.  If we
don't agree on that, I can't see any value in leaving this
unspecified, so let's make them disjoint.

=== #364 truncate, floor, ceiling round should return a non-finite argument ===

Currently R7RS is silent on what truncate, floor, ceiling, and round
do when the argument is `+inf.0`, `-inf.0`, or `+nan.0`. R6RS has them
return the argument, which seems reasonable.

Tests were made for `(round (* 1.0e200 1.0e200))` on a variety of

Racket, Gauche, Chicken (with and without the numbers egg), Bigloo,
Guile, Kawa, Chibi, Chez, SCM, Ikarus/Vicare?, Larceny, Ypsilon, Mosh,
IronScheme, !NexJ, STklos, KSi, Shoe, BDC, Rep, Schemik, Elk, Spark
all return the argument.

MIT, Gambit, Scheme48/scsh, SISC, Scheme 9, Scheme 7, signal errors.

SigScheme, TinyScheme, Dream, UMB don't work for one or another

Oaklisp and Owl Lisp don't do flonums.

XLisp only has fixnums and flonums, and returns the largest or
smallest fixnum as the case may be.

RScheme returns a variety of slightly strange values: (round +inf.0),
for example, is 0, but (round -inf.0) is -inf.0.

Vote `input` to return the input, `error` to specify "it is an error",
and `unspecified` to leave unspecified as in the current draft.

  * '''Options:''' input, error, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' error, unspecified

Rationale: Let's catch errors early.  The whole point of these
procedures is to return integers, so returning something that is not
an integer makes no sense.  If we don't do that, we should leave the
result unspecified rather than force implementations to do the wrong
thing even if it is compatible with R6RS.

=== #392 Exact positive and non-negative integer predicates ===

There are two useful subsets of the exact numbers, both of which are
commonly called natural numbers, depending on who's talking.
Logicians, set theorists, and computer scientists include 0, other
mathematicians mostly don't.  This proposal adds the predicates
`exact-positive-integer?` and `exact-non-negative-integer?`, analogous
to `exact-integer?`.  Because of the ambiguity, the name
`natural-number?` is not proposed.

Vote `yes` to add these two procedures.

  * '''Options:''' yes, no, wg2, undecided
  * '''Default:''' no
  * '''Preferences:''' no, wg2

Rationale: We don't need more names in WG1.

== WG1 - Read/Write ==

=== #380 Is support of TAB as a whitespace character required or not? ===

2.2 says:

Whitespace characters include the space and newline characters.
(Implementations may provide additional whitespace characters such as
tab or page break.)

However, 7.1.1 has:

<intraline whitespace> -> <space or tab>
<whitespace> -> <intraline whitespace> | <newline> | <return>

So 2.2 implies that supporting tabs is allowed but not required, yet
7.1.1 implies supporting tabs is required.

Vote `required` to require support for tab as a whitespace character
by `read`.  `char-whitespace?` is required to return `#t` for it

  * '''Options:''' required, optional, undecided
  * '''Default:''' optional
  * '''Preferences:''' required

Rationale: How can this be in question?  It's just basic ASCII, as is
page break, for that matter.

=== #388 Specify what `display` does with circular lists ===

Currently we don't specify what `display` does with circular lists.
Should it generate labels like `write`, or loop like `write-simple`,
or leave it unspecified?

  * '''Options:''' labels, loop, unspecified
  * '''Default:''' unspecified
  * '''Preferences:''' unspecified, labels

Rationale: Why are we requiring that basic I/O operations be
expensive?  I shouldn't have to allocate memory just to print a list.

=== #447 #!fold-case and #!no-fold-case have no final delimiter ===

The `#!fold-case` and `#!no-fold-case` directives are read as
comments, which means that they are treated as whitespace (section
2.2).  Unlike the other kinds of comments, their final delimiter is
implicit.  This means that `(1#!no-fold-cases)` reads as `(1 s)`.
This seems unfortunate.

  * '''Proposals:'''
    * '''identifier:''' add the formal syntax `<lexical-directive> --> #! <identifier>` and then make the interpretation of `<identifier>` implementation-dependent, except for the standard cases `#!fold-case` and `#!no-fold-case`. (Per Bothner, Richard Kelsey)
    * '''delimiter:''' the directives must be followed by delimiter (John Cowan)
    * '''comment:''' the draft status-quo
  * '''Options:''' identifier, delimiter, comment, undecided
  * '''Default:''' comment
  * '''Preferences:''' delimiter, identifier

Rationale: Requiring a delimiter (presumably including end of file) is
simple and consistent.  Even if we don't do that, we shouldn't stick
with the status quo, which is bizarre.

=== #442 write procedure is not backwards compatible ===

There is concern that the output of `write` cannot be read by non-R7RS
implementations.  This is not a strict requirement, but is reasonable
if using simple sexp-based file/interchange formats.

Specifically, even though there are no cycles in

  `(let ((x (list 2))) (write (list x x)))`

it previously output "((2) (2))" but now outputs "(#0=(2) #0#)".

The WG concern is that R5RS write is unsafe, easily causing infinite
loops, and should therefore not be the default.  Thus we renamed this
"write-simple", requiring programmers to know they are writing a
"simple" data structure up front.

Arguably, there are three procedures desired:

  * write-cyclic: uses labels only to avoid cycles
  * write-shared: uses labels for all shared structure
  * write-simple: won't use labels - it is an error to pass a cyclic structure

although even for `write-shared` people sometimes want to treat
containers such as strings separately.

Note the algorithms for detecting shared structure differ from those
for detecting cycles, so providing both -shared and -cyclic imposes an
additional implementation burden.

  * '''Proposals:'''
    * '''write+simple:''' the current draft status quo
    * '''write+shared:''' change `write` back and add `write-shared` to explicitly handle sharing
    * '''write+cyclic:''' change `write` back and add `write-cyclic` to handle only cycles
    * '''write+shared+cyclic:''' change `write` back and add both `write-shared` and `write-cyclic`
    * '''write+simple+shared:''' `write` handles cycles only, provide `write-simple` and `write-shared` separately
  * '''Options:''' write+simple, write+shared, write+cyclic, write+shared+cyclic, write+simple+shared, unspecified, undecided
  * '''Default:''' write+simple
  * '''Preferences:''' write+shared, write+cyclic, write+shared+cyclic, write+simple+shared

Rationale: We shouldn't make such a basic, incompatible change in a
core language feature (i.e. `write`) even in the interests of
preventing infinite loops.  Furthermore, `write` shouldn't have to
allocate memory just to print something, particularly considering that
the vast majority of uses will have no cycles.

=== #219 Bring back readable boolean literals ===

Scheme used to use `#!true` and `#!false` before abbreviating to
the `#t` and `#f` syntax.

In draft 4 we added these back in as aliases, without the "!" now
that tokens are required to be delimited so there would be no ambiguity.

Some objections were made to the new syntax which generated
a lot of discussion, so we are re-opening this ticket.  The default
is the previous decision to add `#true` and `#false` as aliases.

The primary objection is that boolean literals are very common,
and this introduces needless incompatibilities with non-R7RS
systems, and potential confusion in documentation.

The counter-argument is that these are more readable and
friendly to beginners, and allow easy visual distinction in long lists
of booleans.  We retain full backwards compatibility and are
under no obligation for non-R7RS systems to be able to run R7RS code.

Note that Racket and Chibi independently adopted this same
syntax unaware of each other.  Chicken also supports this via
its SRFI-38 implementation.

  * '''References:'''
  * '''Proposals:'''
     * '''long:''' #true and #false
     * '''bang-long:''' #!true and #!false
  * '''Options:''' long, bang-long, none, undecided
  * '''Default:''' long
  * '''Preferences:''' long, bang-long

Rationale: The long form is more readable, I suppose.  However, I'm
worried that non-R7RS implementations will no longer be able to read
values of this most basic type.

=== #443 Recommend sources of character names ===

Currently, we allow implementations to provide their own names for
characters, but provide no guidance for them.  There are two plausible
sources: the [ names in
the Unicode Standard], and the [
entity names specified by W3C] for use in HTML, MathML, and other
markup standards (ultimately derived from ISO SGML character entity

The Unicode names are in all upper case and contain significant spaces
and apostrophes as name characters, which would require some mapping
to make valid Scheme identifiers.  The W3C name list is incomplete
though fairly large (currently 2237 names), covering mainly the Greek
and Cyrillic scripts and non-ASCII punctuation and symbols.  It
distinguishes between iota (small) and Iota (capital).

Vote `w3c` for the W3C list, `unicode` to use the Unicode list with
names mapped by converting to lowercase and replacing any
non-identifier character (space and apostrophe) with hyphens.  Vote
`unspecified` to leave the character name extensions entirely up to
the implementation.

  * '''Options:''' w3c, unicode, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' unspecified, unicode

Rationale: There isn't agreement among implementations on this.  If we
do specify it, we should specify Unicode to be consistent with all our
other support for Unicode, which is the most carefully thought out
standard in any case.

== WG1 - Base Library ==

=== #140 Removing `quotient`, `remainder`, `modulo` ===

With the acceptance of #278, we reduced the set of division operators
to `truncate-*` and `floor-*` and move these into the base library.
Three of these procedures are simply aliases for `quotient`,
`remainder` and `modulo`, so it is worth considering removing the old

Since the old names are in IEEE Scheme we need strong justification
for removing them from (scheme base), and even if we do so they will
remain available in (scheme r5rs).

We have precedence for changing names, but only in the case when the
existing names were both actively misleading and had already been
changed in R6RS.  Specifically, in ticket #328 we replaced the names
`inexact->exact` and `exact->inexact` with the more accurate `exact`
and `inexact`.

Arguably the new division operator names are clearer, but the old
names are not actually misleading.

Vote `yes` to remove the old names from (scheme base), or `no` to
leave them in as aliases.

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' no

Rationale: I don't have a strong preference, so I'll go with not
breaking existing code.

=== #378 Rename GET-FEATURES to just FEATURES ===

This is compatible with Chicken, and "more Scheme-like, less
Java-like".  Okay, it's bikeshedding.

  * '''Options:''' features, get-features, undecided
  * '''Default:''' get-features
  * '''Preferences:''' features

Rationale: Yes, the "get-" prefix adds nothing here.

We should consider removing it from `get-output-string`,
`get-output-bytevector`, `get-environment-variable`, and
`get-environment-variables` as well.

=== #384 Merge `bytevector-copy` and `bytevector-copy-partial` ===

Under this proposal, the name would be `bytevector-copy` and the
signature would be

  `(bytevector-copy `''bytevector'' [''start'' [''end'']]`)`

Vote `yes` for this simplification.

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: The naming convention "-partial" is neither widely used nor
consistent with naming elsewhere in the draft.

=== #385 Merge `write-bytevector` and `write-bytevector-partial` ===

One proposal is `port-last` with a signature of:

  `(write-bytevector ''bytevector'' [''start'' [''end'' [''port'']]])`

This has the disadvantage of being required to call
`bytevector-length` when writing to a specific port.

Alternately we could do `offsets-last`:

  `(write-bytevector ''bytevector'' [''port'' [''start'' [''end'']]])`

which has the disadvantage of separating the bytevector from its

Alternately, vote `separate` to keep these as two separate procedures.

  * '''Options:''' port-last, offsets-last, separate, undecided
  * '''Default:''' separate
  * '''Preferences:''' port-last

Rationale: Alex says that we should optimize for the most common use
case, and I agree, but I believe that that's writing a range of the
byte vector, not writing to a different port.  After all, as John
points out, the latter can be accomplished using a parameter.

=== #387 Add start/end arguments to string->vector and vector->string ===

This is a proposal to add optional start (inclusive) and end
(exclusive) arguments to `string->vector` and `vector->string`.  We
now have start (inclusive) and end (exclusive) arguments for
`string->list` and `vector->list`, but our non-R5RS and non-SRFI
procedures to convert directly between strings and vectors don't
provide these.

Vote `yes` to add these optional arguments.

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: Yes, these are useful, and we should be consistent.  Alex
says that using indexes with strings is a mistake, but I disagree.
Arbitrarily indexing into a string and expecting to find a well-formed
substring may be a mistake, but it should still be possible to
remember safe offsets while creating a string and use them later.

=== #391 Add predicates for R7RS signalled conditions ===

R7RS requires an error to be signalled (which means an exception is
raised as if by `raise`) in the following circumstances:

 1. Trying to open for input or delete a file that does not exist or is otherwise inaccessible.
 1. Specifying an argument to `scheme-report-environment` that the implementation doesn't support.  (It must support 7 and may support other values.)
 1. An EOF is encountered while `read` is in the middle of a datum.
 1. Using `expt` to raise zero to the power of a non-real number (alternatively an arbitrary number may be returned).

This proposal is to provide four standard predicates that identify
these specific conditions, to be used in `guard` clauses or in
`with-exception` handlers as a portable means of detecting these
errors.  Although these predicates may return `#t` on other objects,
if one reports `#t` on an object, the others must report `#f`.
Proposed names are `file-error?`, `scheme-report-error?`,
`read-error?`, and `expt-error?` respectively.

Vote `yes` to add these procedures, or `file-only` to only add the
`file-error?` predicate, and file+read to add the `file-error?` and
`read-error?` predicates.

  * '''Options:''' yes, file-only, file+read, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes, file+read, file-only

Rationale: I'm disappointed that we have an exception system without a
standard taxonomy even in WG1, so this will provide at least some
relief.  Alex argues that all of these situations can be checked for
in advance, but that's not true.  For example, checking that a file
exists and is accessible before opening it opens one up to a race
condition.  Also, the only way to determine whether EOF will be found
in the middle of reading a datum is to implement a separate parser, at
which point `read` becomes useless.

=== #400 Define record? . ===

We should define the predicate record? so that it's possible to
distinguish instances of record types from all other types.  It should
not be necessary to enumerate all record type predicates in order to
determine whether an object is an instance of a record.

This is Alexey Radul's suggestion.

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: Why shouldn't one be able to distinguish instances of
record types from instances of other types?  John says that having
`record?` would prevent WG2 Scheme from supporting opaque records
because it would be possible to recognize them as instances of record
types.  So what?  What's the harm in being able to recognize them as
such?  Could a programmer do anything malicious with that information?

=== #425 Add read-string, read-string!, write-string procedures to (scheme base) ===

This was requested by Formal Comment #424.

These procedures would be provided for parallelism with the
byte-vector I/O operations:


If #385 passes, optional ''start'' (inclusive) and ''end'' (exclusive)
index arguments would be added to `write-string`.  Otherwise
`write-partial-string` would be provided.

Vote `yes` to add all three, `immutable` to add only `read-string` and
`write-string`, or `no` to leave them out.

  * '''Options:''' yes, immutable, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes, immutable

Rationale: I'm alarmed that we made it this far without

=== #433 full conversion cycle for containers ===

Marc Feeley proposes it should be possible to convert from any
container type to another, possibly via an intermediary such as

  `(list->B (A->list a))`

proposing specifically "list" be the universally available
intermediary, although "vector" would also be worth considering.

The container types are list, vector, string and bytevector.  String
and bytevector are second-class in that they are not general-purpose
container types, and may raise errors converting from lists or

Vote `list` for the proposal to add the following procedures to
complete the cycle:

  * list->bytevector
  * bytevector->list

Vote `vector` to add the equivalent procedures to allow converting
between any of the types and vectors, specifically the following two
new procedures:

  * vector->bytevector
  * bytevector->vector

Vote `list+vector` to add both list and vector conversions.

The `latin-1` proposal also adds the Latin-1-centric ideas of string to
bytevector conversion, where each element of the bytevector is
converted to/from a character with char->integer/integer->char.

The `matrix` proposal requires all 4^3^=64 conversions.

  * '''Options:''' matrix, list, vector, list+vector, latin-1, no, undecided
  * '''Default:''' no
  * '''Preferences:''' no, list+vector, vector

Rationale: I don't see the point.  These conversions are generally
wasteful, especially as simple intermediate values, and direct
conversions would be better.  However, we shouldn't include the full
direct conversions matrix because that's just too large, especially
for WG1.

=== #444 Add vector-append procedure ===

This is for completeness with `append` and `string-append`.  See #436
for the Formal Comment that triggered this ticket.

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: Yes, for consistency and completeness.

=== #451 Add bytevector-append procedure ===

This is for consistency with `append`, `string-append`, and
`vector-append` (per ticket #444) procedures.

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: Yes, for consistency and completeness.

=== #445 Bidirectional ports and port-open? ===

Replace `port-open?` with `input-port-open?` and `output-port-open?`,
since a bidirectional port can be closed on one side without the
other.  See Formal Comment #439.

Vote `replace` to replace `port-open?` with just the two new versions,
or `add` to have all three.

  * '''Options:''' replace, add, no, undecided
  * '''Default:''' no
  * '''Preferences:''' replace

Rationale: Otherwise it's unclear what `port-open?` means on a
bidirectional port.

=== #450 Eliminate default for fill argument in vector-copy ===

Marc Feeley writes:

It is a bad idea for the ''fill'' parameter of `vector-copy` to have a
default. When ''fill'' is absent, it should be an error when ''start''
and ''end'' are not within the bounds of the sequence. Otherwise, some
index calculation errors (off-by-one on ''end'') may go
unnoticed. Moreover, when it is supplied, ''fill'' should also be used
when ''start'' is less than 0, for consistency with the case where
''end'' is greater to the length of the sequence.

Vote `required` to make the fill parameter required, `error` to make
it an error in the case that fill is absent yet needed, `remove` to
remove the fill parameter and signal a runtime error if end is longer
than the input vector, or `default` for the current status quo.

  * '''Options:''' required, error, remove, default, undecided
  * '''Default:''' default
  * '''Preferences:''' remove, error, required

Rationale: While allowing the `fill` parameter to have a default value
is compatible with SRFI 43, Marc's argument about detecting errors is
strong.  However, I disagree that the idea of allowing `start` to be
negative is somehow more consistent.  The obvious application of the
`fill` parameter is implementing variable-length data structures out
of vectors, extending the original in the process.  However, using the
name `vector-copy` for this purpose is an awkward overloading.  A
separate procedure, not defined in WG1 Scheme, should be used for that

I've updated WG1Ballot, so others should adjust their votes if they
see fit.

=== #404 Make handlers take a raise-continuable? argument. ===

Pass exception handlers a second, Boolean argument that declares
whether the exception is continuable.

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' no

Rationale: I would like to see this, too, but agree that passing it to
every handler is overly verbose considering how rarely it would be
used.  We should address this in WG2 where we will, I hope, have a
more powerful exception system.

=== #464 Add optional start and end parameters to utf8->string and string->utf8. ===

Per ticket 464, add optional start and end arguments to `utf8->string`
and `string->utf8`.

Vote `both` to add optional start and end arguments to both,
`string->utf8` or `utf8->string` to add them to only one procedure, or
`neither` to leave both unchanged.

  * '''Options:''' both, string->utf8, utf8->string, neither
  * '''Default:''' neither
  * '''Preferences:''' both, utf8->string, neither

Rationale: As Marijn says, it's useful to be able to avoid extra
copying while decoding a string.  We should change both for symmetry.

== WG1 - Optional Libraries ==

=== #373 (exit #t) should be the same as (exit) ===

See Formal Comment #372 for the argument.  Cowan writes: "I support this proposal.  I
don't support the alternative proposal to just say that any true value
reports success and only #f reports failure, for there is usually only
one kind of success (0 on Posix and Windows, "" on Plan 9, 2 on VMS)
and many kinds of failure."

It is reasonable and convenient to use `#t`/`#f` as generic
success/failure for portable programs, with `(exit)` as a shorthand
for the "normal" completion `(exit #t)`.

Another reasonable extension is fallback for certain success values
that the implementation cannot understand.  Specifically, `0` is
commonly used for success on Posix systems, and the empty string "" as
success on Plan9.  We could require that if the implementation does
not know how to pass these value types (string or number) to the OS,
then it should recognize `0` and `""` as true.  Any value other than
these which cannot be passed to the OS should be treated as a generic
error.  That way, a program written for Posix that alternatively uses
`(exit 0)` and `(exit <n>)` will still work as desired on a Plan9
system, only losing details of the type of failure (and likewise for
Plan9 programs running on Posix).

In either case, unless someone makes a proposal to the contrary,
unknown values should always be treated as generic failure, and never
raise an exception or fail to exit (from #374).

  * '''Proposals:'''
    * '''boolean:''' Only `#t`/`#f` are as described as above, and all other values are passed (as best as possible) to the OS and therefore implementation-defined
    * '''extended-true:''' `#f` is generic failure, `#t` generic success, and `""` and `0` are generic success if not otherwise understood by the OS
  * '''Options:''' boolean, extended-true, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' boolean, unspecified

Rationale: Making `(exit #t)` have the same effect as `(exit)` is a
no-brainer.  I can see no portable reason to treat the empty string
and zero specially.

=== #375 Add EMERGENCY-EXIT procedure ===

This procedure provides instant guaranteed process exit without
running `dynamic-wind` thunks.  This is a low-level and dangerous

Vote `emergency-exit` to add this procedure, or `no` to leave it out.
If you want to write in an alternate name, be sure to include
`emergency-exit` as a secondary option after it.

  * '''Options:''' emergency-exit, no, undecided
  * '''Default:''' no
  * '''Preferences:''' exit-immediately, emergency-exit

Rationale: I hate the name, but it makes sense to be able to exit
immediately.  Frankly, I'd rather that `exit` did this, or that its
behavior with regard to `dynamic-wind` was unspecified.  It's my
impression that people use `exit` when they want their program to stop
immediately.  They don't want a `dynamic-wind` form to prevent their
exit, for example.

I suggest the name `exit-immediately`.


Cowan writes:

"I have reluctantly come to the same conclusion as the R6RS editors:
that in a Scheme with libraries, `scheme-report-environment` and
`null-environment` don't make much sense.  They are not in IEEE Scheme
or R4RS, so there is no formal barrier to removing them.

"Semantically, `scheme-report-environment` holds all the identifiers in
R5RS, excepting any which the implementation doesn't provide, like
`make-rectangular` if it does not have complex numbers.
`Null-environment`, on the other hand, contains only the syntax
keywords with none of the standard procedures: it is not an empty
environment.  R6RS preserves these procedures only in the R5RS
compatibility library, where they expose only R5RS content.

"When adapting the definition to R7RS, I changed
`scheme-report-environment` to contain all the identifiers in all the
standard libraries that the implementation provides, and
`null-environment` all the syntax keywords in those libraries.  This
was the best I thought I could do, but now I think that it provides
very little utility.

"It's possible to construct any specific environment you want by using
the `environment` procedure, which turns a sequence of import-specs
into an environment.  In particular, we now have the `(scheme r5rs)`
library, which essentially provides what
`(scheme-environment-procedure 5)` should provide, and there is no
portable use of any argument other than 5."

Vote `remove` to remove these two procedures entirely, or `move` to
move them from (scheme eval) and provide them only as portability
options in `(scheme r5rs)`, where only the argument 5 is required to
be supported.  Vote `keep` to leave them as-is.

  * '''Options:''' remove, move, keep, undecided
  * '''Default:''' keep
  * '''Preferences:''' move, remove

Rationale: I see John's point, but we shouldn't break compatibility
with R5RS.

=== #413 EVAL accepts DEFINE ===

The proposal is to require `eval` to accept definitions as well as
expressions, as long as the specified environment is mutable.  See
EvalDefine for which Schemes already handle this.

  * '''Options:''' yes, no, unspecified, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: `eval` should accept the full language, including defines.

=== #399 clarify which primitives are allowed to implicitly force ===

The standard allows the following extension to force:

  Some implementations may implement "implicit forcing," where the
  value of a promise is forced by primitive procedures like `cdr'
  and `+'

We should remove this note or tighten the definition.

A simple definition is any primitive that would require a type-check
can perform implicit forcing.  This would include all type predicates
themselves except for `promise?`.  Note if #405 passes, then in
implementations which support this extension an object could return
`#t` for `promise?` in addition to one other type.

  * '''Options:''' remove, type-check, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' unspecified

I don't see any reason to change this.

=== #405 Make promises first-class ===

Currently there is no way to inspect an object to see if it's a
promise.  This proposal makes promises first-class by adding a
`promise?` predicate.  It also requires that if the argument to
`make-promise` is a promise, it is returned without rewrapping it, and
that if `force` is given a non-promise argument, it returns it
unchanged.  (These things cannot be provided by the user without a
`promise?` predicate, and are trivial to provide with it.)

Vote `disjoint` to add `promise?` and make it a disjoint type, or
`yes` to add it as a not-necessarily disjoint predicate.

  * '''Options:''' disjoint, yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' disjoint, yes

Rationale: The `promise?` procedure is useful, as the examples above
demonstrate.  Once we support `promise?`, keeping them disjoint seems
easy, since if one implements them directly as procedures, one can't
provide `promise?` without an inefficient table lookup anyway.

=== #462 end of line definition ===

The definition of read-line allows implementation defined extensions
to the set of end of line sequences. This is arguably too loose, as an
implementation could define "a" as and end of line. On the other hand,
if we do want to leave this in it may make sense to remove "\r", which
is no longer used in any contemporary OS.

Vote `no-extensions` to forbid implementation defined extensions,
`no-return` to remove a single return from the list of required end of
lines, and `none` to leave as-is.

  * '''Options:''' no-extensions, no-return, none, undecided
  * '''Default:''' none
  * '''Preferences:''' none, no-return

Rationale: Implementations are going to define extensions, and it's
unreasonable to expect them not to.

=== #452 provide digit-value support for non-decimal-digits ===

In ballot 4, in symmetry with the new Unicode definition of
`char-numeric?` and as an analog to CL's `digit-char-p`, we provided

An informal comment was made questioning this procedure, and
suggesting if provided at all it be extended to hex digits.

Vote `ascii-hex` to support only the ASCII hex digits a-f,A-F (in
addition to full Unicode numeric digits), `unicode-hex` to support all
Unicode variants of a-f,A-F (need to define formally).

Vote `ascii-radix` or `unicode-radix` to have both `digit-value` and `char-numeric?` take a radix argument, such that `char-numeric?` returns #t and `digit-value` returns the appropriate value for characters representing non-numeric digits of that radix under ASCII or Unicode character encodings, respectively, and for characters representing numeric digits under Unicode.  Implementations are required to support at least the radix values: 2, 8, 10, and 16, and may support others.

Vote `remove` to remove `digit-value` entirely, `remove-radix` to remove `digit-value` entirely, but add the radix argument to `char-numeric?` as described above, or `keep` to keep as is.

  * '''Options:''' ascii-hex, unicode-hex, ascii-radix, unicode-radix, remove, remove-radix, keep, undecided
  * '''Default:''' keep
  * '''Preferences:''' remove, ascii-hex

Rationale: We've strayed into invention territory here, providing
something that existing implementations don't.  If we do keep it, it
should support ASCII hex for compatibility with `string->number`.

== WG1 - Non-normative ==

=== #411 Reference implementation ===

Our charter calls for one or more reference implementations.  As of
today, Chibi is very close to being so.  The proposal is to bless it
as a sample or model implementation, but not technically a reference
implementation -- if it disagrees with the standard, the standard

  * '''Options:''' yes, no, undecided
  * '''Default:''' no
  * '''Preferences:''' yes

Rationale: Chibi is the one implementation that be considered a
reference implementation, and we are supposed to provide one, so let's
make it official.  Thank you very much to Alex for doing the work to
make this happen.

=== #463 library naming conventions  ===

We currently use the singular form of data types for library names,
e.g. `(scheme char)` and `(scheme file)`.  R6RS prefers the plural, as
in `(scheme lists)` and `(scheme records)`. We should decide
officially which is preferred.

  * '''Options:''' singular, plural, unspecified, undecided
  * '''Default:''' unspecified
  * '''Preferences:''' singular, plural, unspecified

Rationale: I'll bikeshed for the singular.  (I'm assuming that what
we're saying here is that we'll change all of the data type names we
use, not that we're saying anything about the names people use for
purposes other than standard data types.)

== WG1 - Late additions ==

=== #465 Add jiffy-modulus to specify when, if ever, current-jiffy wraps ===

If the value of `current-jiffy` is to be both space-efficient (that is, a fixnum) and reasonably precise (say, microsecond timing), it needs to wrap around: 30-bit fixnums on a 32-bit system will wrap every 17 minutes.  That means an application needs to know what the maximum value is before it wraps back to zero.  The `jiffy-modulus` function returns the maximum value of the current jiffy plus 1.  Alternatively, jiffies can be signed and wrap from (- (jiffy-modulus) 1) to (- (jiffy-modulus)), which is easier for the implementation but harder for the user.

  * '''Options:''' unsigned, signed, no, undecided
  * '''Default:''' no
  * '''Preferences:''' undecided

Rationale: I don't know what existing implementations do.

=== #466 case folding of character names ===

In ticket #11 we voted to make the reader case-sensitive
by default. In ticket #92 we further added the R6RS
#!fold-case and #!no-fold-case reader extensions. In
both cases the terminology was lax and simply referred
to "reader case sensitivity", and all discussion centered
around symbols, although in R6RS character names were
also affected.

Case folding will apply to numeric literals, booleans and
bytevectors regardless, as they do in both R5RS and R6RS.
We need to clarify how character names and the case
folding directives themselves are handled.

The default is `r6rs`, where character names are case
sensitive by default and folded by the `#!fold-case` flag:


Alternately character names could be made to ignore
the reader directives and always or never fold case.
Never folding case breaks R5RS and earlier compatibility
without any easy workaround.

These same settings apply to the `include-ci` syntax.

  * '''Proposals:'''
    * '''r6rs:''' character names behave like symbols, directives are sensitive
    * '''r6rs+directives:''' like `r6rs` but directives can also be case-folded
    * '''always-fold:''' like `r6rs` but character names and directives always fold case
    * '''never-fold:''' like `r6rs` but character names and directives never fold case
  * '''Options:''' r6rs, r6rs+directives, always-fold, never-fold, undecided
  * '''Default:''' r6rs
  * '''Preferences:''' r6rs, r6rs+directives

Rationale: I see no reason to differ from R6RS here.

=== #467 Allow eqv? and eq? to return different answers on procedures as well as integers and characters ===

This proposal stems from [ remarks] by Alaric Snell-Pym and Will Clinger on the r6rs public mailing list.  If `eq?` is allowed to return `#f` on two procedures when `eqv?` nevertheless returns `#t`, as is already the case for numbers and characters, then more intelligent implementation-specific procedure comparisons using `eqv?` are possible, while still keeping `eq?` simple enough to inline easily.

Note that this is orthogonal to the question of #460, how `eqv?` works on procedures.  There should be little or no backward-compatibility hit for this change.

  * '''Proposals:'''
    * '''same:''' `eq?` and `eqv?` always return the same on procedures, per R5RS and R6RS
    * '''different:''' `eq?` may return `#f` on procedures even when `eqv?` returns `#t` (but not vice versa)
  * '''Options:''' same, different, undecided
  * '''Default:''' same
  * '''Preferences:''' different

Rationale: I will defer to Will's long experience in compiler implementation.


2012-09-16 07:07:09