This site is a static rendering of the Trac instance that was used by R7RS-WG1 for its work on R7RS-small (PDF), which was ratified in 2013. For more information, see Home. For a version of this page that may be more recent, see WG1Ballot5Results in WG2's repo for R7RS-large.

WG1Ballot5Results

alexshinn
2012-04-09 18:46:13
4updating missing Shinn vote for #275history
source

Notes about Results

See WG1BallotExplanation.

WG1 Ballot Items To Finalize By Mar. 31

WG1 - Core

#229 Are NaN values EQV?

We voted that eqv? return #t if both arguments are any value which writes as +nan.0. The description of this item was ill-formed and confusing, as objected to in:

http://lists.scheme-reports.org/pipermail/scheme-reports/2011-September/001507.html

We therefore are re-opening the item, with amended descriptions.

The different proposal is that we add a single clause requiring (eqv? +nan.0 x) to return #f for any x. This is the behavior that results for any R5RS implementation that adds support for +nan.0 as an IEEE float without any special handling for it in eqv?.

The unspecified proposal is to make the results explicitly unspecified, as specified in R6RS.

The same proposal, contrary to both standards, is that we add a clause to the definition of eqv? saying that if both arguments are NaN values with the same bit pattern, eqv? must return #t. Thus eq? implies eqv?. However, if two values both print as +nan.0 they may or may not be eqv?. This also requires additional checks for floating point comparisons.

Testing with (equal? (/ 0.0 0.0) (/ 0.0 0.0)) to get the same bit pattern but non-object-identity, we get the following results:

The following 8 implementations return #t: Chez, Gambit, Guile, Ikarus/Vicare, Kawa, Larceny, Racket, STklos.

The following 6 implementations return #f: Bigloo, Chibi, Chicken, Gauche, MIT Scheme, Scheme48.

SigScheme and Scheme 9 don't have +nan.0. SISC currently has a bug where (= nan.0 x) is true for any x.

Gleckler
I don't see any reason to differ with R6RS here. It's easy for implementations that follow the "different" option to switch to supporting the "same" option. Furthermore, Bradley Lucier and Will Clinger appear to have thought about it a lot and have come to the same conclusion, so I'm more confident.
Lucier
I believe that I now understand what this issue is about. First of all, Gambit might return #f or #t on a PowerPC system, depending on how the NaN is computed; I suspect the same might be true for other Schemes. Depending on the computer system, many values that print as +nan.0 may have different bit patterns. So, if (number->string x) => "+nan.0" and (number->string y) =? "+nan.0" and the bit patterns of x and y differ, then I believe that (eqv? x y) => #f On the other hand, eqv? is supposed to be an equivalence relation, so it is reflexive, so (let* ((x (/ 0. 0.)) (y x)) (eqv? x y)) => #t and both x and y satisfy (number->string x) => +nan.0 (number->string y) => +nan.0 So I believe that unspecified is the best option.
Medernach
NaNs are provided as a diagnostic tool to help understand errors in number computation. As such we need to have a way to distinguish different NaNs, therefore the 'same' vote.
Shinn
We need to handle this directly in the definition of eqv?. As the current definition stands, if specified at all it must be different.

#275 Support -nan.0 as a synonym for +nan.0

Excluding -nan.0 was an oversight, and it's gratuitously incompatible with R6RS as well as current practice. Racket, Gauche, Chicken, Guile, Chez, Ikarus, Larceny, Ypsilon, STklos all support +nan.0 and -nan.0 as equivalent forms. MIT, Bigloo, Scheme48/scsh, SISC, SCM, Scheme 9 don't support either form. Only Gambit and Chibi support +nan.0 but not -nan.0.

STklos prints both +nan.0 and -nan.0 as -nan.0.

Vote yes to allow -nan.0, no to disallow it.

Cowan
If -nan.0 is not a number, it's an identifier -- but almost all Schemes that handle +nan.0 at all treat -nan.0 as a number. We don't want to demand that they allow code treating it as an identifier. Nobody needs to remember -nan.0 except not to use it as an identifier.
Gleckler
I agree with Alex. There's no point in having this extra identifier. It has no meaning. If the option were option, I'd rather that we replaced "+nan.0" (and "-nan.0") with the identifier "NaN" now that we're case-sensitive. It would be unlikely to conflict with existing code, and it wouldn't be quite as ugly.
Lucier
Eventually, some Scheme should allow one to see all the bits of a NaN (as this is true for all other floating-point numbers). This is a good step in that direction.
Medernach
The sign bit of NaNs is meaningless in the IEEE Standard 754 floating-point formats, but in order to avoid using it as an identifier we may consider both as synonymous. However I really would prefer using NaN instead of +nan.0 or -nan.0 (as it is not a number but an indication of failure, to help diagnostic, it is neither signed in general, nor exact nor inexact, isn't it ?)
Shinn
I don't understand the motivation behind this. NaN can neither be positive nor negative - the "+" is just a hint that the value is numeric (which is no longer true with the symbol extensions that now allow an initial "+"). Thus "-" serves no purpose and does not simplify the syntax - if we allow multiple forms, do we also allow "nan.0", "+nan.", "+nan", "+nan.1", etc.? One is easier to remember than two.

#278 Shrink division routines to just truncate and floor

Bradley Lucier says:

I don't see the centered-* operators as somehow a "completion" of the other division operators. In the small language I'd recommend only the truncate-* and floor-* operators for two reasons: they are the only division operators that have an established history of use in computer programming and mathematics, and they form a minimal extension of R5RS. (I'm not saying that the other division operators have never been used in mathematics or programming (see CL), but small Scheme is not supposed to be a kitchen-sink language.)

Vote shrink to prune to truncate-* (R5RS) and floor-* (R5RS modulo), moving the extra operators to the large language; shrink/core to do the same as shrink but move the remaining operators to the core language; or keep to keep all 18 division operators in the small language.

Cowan
I think enough justification exists for each of the six operations. I agree that if we do shrink, we should get rid of the division module.
Gleckler
I see no new evidence justifying a change from our initial vote. I encourage people to read the cited paper, "The Euclidean definition of the functions div and mod," <http://dl.acm.org/citation.cfm?id=128862>. Here's an excerpt: Indeed, the functions div and mod are very important concepts in discrete mathematics for certain problems in number theory, in computer science for reasoning about number representation systems, in communications engineering for a variety of issues ranging from coding to sampling and multiplexing, and so on. Hence it is unfortunate that the definition of these functions appears to be handled rather casually in the computer science literature and in the design of programming languages, as one might infer from various poor "definition...
Lucier
I've read Taylor Campbell's reply and I don't find it compelling. To paraphrase one of his arguments somewhat, I don't find "If we have floor-divide we need ceiling-divide" compelling---we've gotten along reasonably well without either of them so far, but we could get floor-divide from R5RS quotient and modulo from (define (floor-divide x y) (quotient (- x (modulo x y)) y) Module is an important operation, there should be a division operator associated with it. I can't say that the other non-R5RS remainder or division operators are "important". I do believe that R7RS small scheme should just complete the three division/remainder operators in R5RS with floor-divide (or whatever the name should be ) and leave the rest to R7RS big scheme.
Medernach
Relegate additional operators to the large language and put truncate-* and floor-* back to the core.
Shinn
I agree completely. The operators need more use and individual rationales before they are promoted to the small language. I'm also voting shrink/core to suggest we put them back in the core language, iff we shrink.

#280 Make vectors self-quoting

Currently vectors are the only type represented by a readable datum that are neither self-quoting nor meaningful Scheme expressions (i.e. symbols and lists). The proposal is to make them self-quoting as well.

Currently Racket, Gauche, MIT, Guile, Kawa, Chibi, SCM, STklos, Scheme 9, Scheme 7, UMB, VX, Oaklisp treat vectors as self-quoting.

Gambit, Chicken, Bigloo, Scheme48/scsh, SISC, Ikarus, Larceny, Ypsilon, IronScheme, Mosh, KSi, SigScheme, Elk treat unquoted vectors as errors.

Vote yes to make them self-quoting, no to make it an explicit error, or unspecified to leave unspecified as in R5RS.

The only other reasonable alternative semantics for this unspecified case would be to treat #(...) as (vector ...) (i.e. in contrast to this proposal to evaluate the contents rather than quoting them). No known implementations make this extension, and it is dubious due to the fact that it makes what appears to be quoted data to be evaluated, and so is not listed as an option. The possibility of this extension, however, could serve as an argument to leave it unspecified.

Cowan
I think this will be awkward for the R6RS implementations, since R6RS requires an error to be signalled. Other than that, I'm for this and always have been. I proposed it during the R6RS formal-comment process, and it was rejected with "Generally, Scheme has often favored uniformity over succinctness". Still, what's done is done. I'm still voting "yes".
Gleckler
Alex assured us that this wouldn't make things like `#(1 ,(+ 2 3)) fail, so I'm voting yes.
Hsu
I am unsure whether I am willing to say that vectors are inherently not meaningful Scheme expressions. I can imagine an extension that allows one to say something like #(5 (+ 1 2)) ; => '#(5 3). Implicit quoting would disallow this extension and others.
Medernach
What about square brackets syntax ? This is natural notation for vectors.
Shinn
This is fairly widely supported and is the only reasonable semantics for unquoted vectors.

#282 Map and friends should call their procedures in the same dynamic environment

The specifications of map, for-each, and other procedures that accept a procedure as an argument and call it, should specify that the argument procedures will always be called in the dynamic environment of the call to map, for-each, etc.

This is an R6RS fix.

Vote yes to add the clarification and no to leave it out.

Gleckler
This is too obvious to be worth specifying. Furthermore, if we specify it here, what are we implying about other procedures like this?
Hsu
This is a good clarification and not harmful.
Shinn
That the semantics are desired is obvious, but I don't see how they could be interpreted otherwise and I'm not convinced it's worth writing this.

#283 Initial characters in non-ASCII identifiers should exclude digits and combiners

Identifiers beginning with a character of type Nd, Mc, or Me should be forbidden. This is an R6RS issue.

Nd is a numeric character, which in the case of ASCII 0-9 is already forbidden, but currently unspecified for non-ASCII digits.

Mc and Me are enclosing marks and spacing combining marks respectively, which are logically attached to the preceding character.

Vote yes to forbid (which would still allow this as an implementation-dependent extension for either numbers or symbols).

Gleckler
This is an obvious choice for consistency of implementations that support Unicode.
Hsu
I do not know enough about how this will affect things to say for sure.
Shinn
This makes sense - such identifiers would look like numbers which would be misleading.
SnellPym
I still feel that any character should be legal in a symbol, if not necessarily possible to represent without quoting, and that any symbol should be legal as an identifier!

#285 R6RS base compatibility: symbol=?

This is equivalent to eq? on symbols, and provides R6RS base compatibility as well as completing the set of type-specific comparisons. See also #316.

Vote yes to add this procedure.

Cowan
This helps with type-inference, although in practice the large language will want to provide some form of identifier=?.
Ganz
I agree with Arthur's comment on uninterred symbols
Gleckler
I agree that this is needed to complete the set of type-specific comparisons. Since the standard specifically mentions the possibility of uninterned symbols, the description of symbol=? should say something about what it means in implementations with uninterned symbols. It would probably be best to say that its behavior is unspecified when either argument is an uninterned symbol. Normally, we wouldn't have to say anything about an extension to the language, but since we already talk about this extension, it's justified.
Lucier
We need this why?
Medernach
I feel that non composed types doesn't need type-specific comparisons functions as we have generic 'eq?' or 'eqv?'. This looks unnecessary to provide a trivial composition of symbol? and eq?.
Shinn
This helps with type-inference, although in practice the large language will want to provide some form of identifier=?.
SnellPym
Consistency is good.

#286 Numeric *-valued procedures for R5RS and R6RS-base compatibility

Real-valued?, rational-valued?, and integer-valued? test whether a given number object can be coerced to the specified type without loss of numerical accuracy. They are equivalent to the versions of real?, rational?, and integer? that exist in R5RS.

Specifically, the behavior of these predicates differs from the behavior of real?, rational?, and integer? on complex number objects whose imaginary part is inexact zero.

These procedures provide R6RS base compatibility as well.

Cowan
It's inconsistent to vote for the R6RS-base library without providing these. In addition, the R5RS library can and should export them as real, rational, and complex. This is one of the places where we made a silent change to the semantics of a procedure (silent in the sense that code will behave differently without any warning), and there should be an easy way to recover the old semantics.
Ganz
The example given is too narrow to support both sets of predicates.
Gleckler
These names are awful. I'll never be able to remember that real-valued?' means something different than real?', and even if I do, I won't remember which one is which. I'm sure others will have the same problem. If we come up with better names, I might be willing to vote yes. After John's edit: The "strictly-*" names don't make things any less confusing, so I'm voting to revert to r5rs or at least to leave out the new names.
Shinn
If nothing else the names are too confusing - the difference is too small, and I don't think people will be able to keep these straight.

#287 R6RS base compatibility: assert

Assert raises an error if its argument is #f. This provides R6RS base compatibility.

Vote basic to add this syntax. Vote optionals to make assert optionally accept, after its expression argument, a single message argument and zero or more irritant arguments in the same manner as the error procedure. Vote no in order not to add assert.

Cowan
It's inconsistent to vote for r6rs-base without adding this. People who don't like it are free to import the base library without it and define their own.
Gleckler
We shouldn't include assert' without making it at least equal to error' in its ability to describe a problem. If we can't do that, we should wait for implementations to come to agreement rather than specifying something anemic.
Hsu
Assert is very useful, but much less so without message arguments.
Medernach
However I agree that 'assert' is popular, it is superfluous in the WG1 language because it adds little to 'error', and WG2 may come with something more powerful like contracts (a la Eiffel as in "Contracts for Higher-Order Functions" and as provided by Racket).
Shinn
There are numerous assert macros, and it's not clear which is best - in particular, the best ones allow friendlier reporting. This isn't ready for the small language.
SnellPym
I vote for the optionals as I think it should provide all the functionality of the inner error.

#288 R6RS base compatibility: infinite?

Infinite? returns #t if its value is a real number, or if its value is a complex number and either the real or the imaginary part would return #t to infinite?. This provides R6RS base compatibility, with extensions for complex numbers analogous to that provided by finite? and nan?.

This was in the draft at one point, but was never actually voted on, so the editors removed it.

Vote yes to add this procedure.

Gleckler
Sounds reasonable.
Shinn
I more often want to check infinite? than finite?.

WG1 - Numerics

#290 Proposed square procedure

Bradley Lucier writes (lightly edited):

A square primitive is useful in calculating with bignums because squaring a bignum is generally cheaper than multiplying two different bignums of the same size. For example, Gambit's runtime checks trivially whether the two arguments in (* a b) are eq? before calling the appropriate algorithm. Generally, it may be better to be able to express this primitive directly.

[He also points out that given square in the small language, we can have flsquare in the large language, though having the latter doesn't actually require having the former.]

In addition, there are 20,340 Google hits for ["(define (square x)" ss|scm].

Vote yes to add this procedure.

Cowan
On the one hand, (expt x 2) is the same thing, and should be just as easy to optimize. On the other, we provide sqrt as an alias for (expt x 1/2) and it seems odd not to have this inverse.
Gleckler
I buy the argument from symmetry with `sqrt'.
Shinn
On the one hand, (expt x 2) is the same thing, and should be just as easy to optimize. On the other, we provide sqrt as an alias for (expt x 1/2) and it seems odd not to have this inverse.

WG1 - Core

#291 Require an error to be signalled if input files cannot be opened

For with-input-from-file, with-output-to-file, call-with-input-file, call-with-output-file, R5RS just says that the file should exist. However, open-input-file requires an error to be signalled if the file cannot be opened, whether because it does not exist for some other reason like the lack of permissions. This inconsistency doesn't seem useful.

The proposal is to change these wrapper procedures to also require an error to be signalled if the file cannot be opened. All major Schemes already implement this.

Vote yes to require signalling an error if the files cannot be opened.

Gleckler
Yes, this error shouldn't happen silently. Since implementations already signal it, this change won't be a problem.
Shinn
I think R5RS implies this behavior, but it's worth making explicit.
SnellPym
Forcing an explicit error signal means that portable code can know how to handle this error case by catching the signalled condition.

#292 Add case-insensitive normalization-insensitive comparisons

mdmkolbe writes on Slashdot:

Given that on a system with Unicode, you almost never want to do a non-normalizing case-insensitive match and that it is hard for a user to efficiently implement their own normalizing case-insensitive match, it seems an odd corner of the rectangle to omit.

(end quotation)

Alternatively we could specify that -ci procedures always normalize, or that -ni procedures are always case-insensitive, since the details of the normalization are not exposed anyway.

Cowan
Alex says: "I think this point suggests that the normalization API doesn't compose well, and needs to be thought out better. I'd rather remove it and provide something more powerful in the large language." I agree, though I'd like to allow *-ci to do implementation-defined normalization, since it basically exists to do human-friendly matching.
Gleckler
I don't feel confident about Unicode decisions, so my inclination is to remove these procedures if there's any disagreement. If we don't remove them, we should complete the rectangle.
Shinn
I think this point suggests that the normalization API doesn't compose well, and needs to be thought out better. I'd rather remove it and provide something more powerful in the large language. Otherwise, we should leave it as is.
SnellPym
I'm not really sure when I'd want to do a NON-normalising string comparison, to be honest, as it would tend to reflect spurious differences due to the details of Unicode encodings. Whether it's case sensitive or not is the only choice I'd like to make.

#293 Make it an error for <test> values to return other than one value

Currently nothing is said about the <test> of if, cond, and, or, etc. returning zero values or multiple values. The proposal is to make this an explicit error. Remember that this does not mean an error is signalled.

Vote yes to make an explicit error.

Cowan
As the standard already says, "Except for continuations created by the call-with-values procedure [...] all continuations take exactly one value. The effect of passing no value or more than one value to continuations that were not created by call-with-values is unspecified." Repeating this information for every continuation that could not be created by call-with-values is redundant.
Gleckler
The standard already makes this clear in a general way. There's no way to repeat that information for conditionals in particular.
Medernach
This has to be unspecified because many implementations differ on this issue.
Shinn
As the standard already says, "Except for continuations created by the call-with-values procedure [...] all continuations take exactly one value. The effect of passing no value or more than one value to continuations that were not created by call-with-values is unspecified." Repeating this information for every continuation that could not be created by call-with-values is redundant.
SnellPym
I'd like it to be explicitly legal, and that the first value is taken; and this should be reflected consistently everywhere N values are expected, that any extra values are ignored and it's an error only to have less than N.

#294 Make it an error for the <expression> of a set! to return other than one value

Currently nothing is said about what happens if the <expression> of a set! returns zero values or multiple values. The proposal is to make this an explicit error. Remember that this does not mean an error is signalled.

Vote yes to make an explicit error.

Cowan
Same argument as for #293 above.
Gleckler
Same argument as for #293: this is already clear, and repeating it would be redundant.
Shinn
Same argument as for #293 above.
SnellPym
Same rationale

#295 Make it an error for <init>s in binding forms to return other than one value

Right now nothing is said. The proposal is to make this an explicit error. Remember that this does not mean an error is signalled.

Vote yes to make an explicit error.

Cowan
Same argument as for #293 above.
Gleckler
Same argument as for #293: this is already clear, and repeating it would be redundant.
Hsu
This should be tied to our definition of what happens when multiple values are sent to a single valued context. Specifically, there should be no difference in semantics between the lambda transformation of let and normal let.
Shinn
Same argument as for #293 above.
SnellPym
Likewise

#297 Removing case-folding flags

The case-folding flags #!fold-case and #!no-fold-case are the only reader flags in the draft, however their need is reduced (though not eliminated) by the library declaration include-ci. Do we still need flipflop flags to turn case-folding on and off in part of a file?

If we remove these we maintain backwards compatibility with R5RS library code, however we lose the ability to support R5RS programs or toggle case-folding in the REPL or data files, etc.

Cowan
We could only remove these in conjunction with a proposal that allows toggling case-folding in the REPL.
Gleckler
I'm opposed to making Scheme case sensitive, but have lost that argument. However, even R6RS supported these flags at least optionally, and it shouldn't be necessary to construct a module just to load old code that depends on case sensitivity.
Hsu
These are too convenient to remove and not all cases are adequately handled by include-ci.
Shinn
We could only remove these in conjunction with a proposal that allows toggling case-folding in the REPL.
SnellPym
I've never liked these - they just seem inelegant.

#303 "lazy" is a confusing name

[Based on feedback from Marc Feeley.]

delay and force were simple balanced concepts, but the introduction of lazy somewhat confuses the issue - when is delay appropriate and when is lazy? A simple solution would be to rename lazy to delay-force, indicating it is simply the composition of delay and force, and letting people see directly in code the balance of delays and forces.

Cowan
lazy is confusing, delay-force makes the usage and the relation to existing operators obvious.
Gleckler
This name makes the purpose clearer.
Shinn
lazy is confusing, delay-force makes the usage and the relation to existing operators obvious.
SnellPym
I like that reasoning.

#304 symbol literal syntax wastes characters

[Based on feedback from Marc Feeley.]

Currently symbols can either be delimited with pipes |...| with optional hex escapes inside, or include hex escapes directly without the pipes. This wastes two characters that were reserved in R5RS, the pipe and the backslash, when either one by itself would be sufficient to represent all symbols. This is especially unfortunate because both characters are used as extensions in various Schemes - the pipe being another symbol character in SCSH (to represent shell-style pipes and C-style operators) and the backslash used in Gambit's infix syntax. We should reconsider if we really need to take up both of these characters.

We can also consider new sequences, for instance \|...| with optional hex escapes inside uses only \, has the readability advantages of |...|, and still leaves room for other \ escapes since the following | character is required. However, such new sequences have no existing support among implementations.

Cowan
Both is a waste - I prefer either-or. Although the uses in SCSH are nice, the |...| syntax is very widely implemented.
Gleckler
As others have said, the |...| syntax is widely implemented. I don't think the backslash-only syntax is widely implemented.
Hsu
I like both of these forms, but I think that the composition of the two is a mistake. Specifically, you should not be using internal escapes, and as such, I have added my own option here, to remove the use of internal escapes inside of the pipes.
Shinn
Both is a waste - I prefer either-or. Although the uses in SCSH are nice, the |...| syntax is very widely implemented.

#305 Should we move the c...r and c....r procedures into a new library?

They have been required for a long time, but Alex Shinn says:

I definitely think everything but the one and two depth combinations should be removed from (scheme base). Their use is generally a code smell. People should use destructuring, records, or SRFI-1 first..tenth accessors.

Ray Dillinger (Bear) adds:

The historic use of these entities was as accessors for structured aggregates implemented with cons cells. In a language that directly supports records, they have a reduced mission.

Vote base to keep all in the base library or library to move the 3- and 4-letter accessors to a separate library.

Cowan
I think removing them is too strong, but would like to be able to trim down the base library of 24 marginal-use procedures.
Gleckler
They have a long history and are used in lots of code, so we shouldn't remove them. However, moving them to a library is a good idea. What shall we call it?
Shinn
I think removing them is too strong, but would like to be able to trim down the base library of 24 marginal-use procedures.
SnellPym
I concur with the submitted arguments.

#307 "eager" is a confusing name

[Based on feedback from Marc Feeley]

The eager procedure is named particularly unfortunately because it sounds as though it is in some way paired with lazy, and there is anecdotal evidence it was voted in on this misunderstanding. In fact, it is completely unrelated to lazy, being just a utility procedure that has never been seen used in practice. Perhaps a better name for it would be promise or make-promise, since it just creates an (already computed) promise value.

Vote eager, promise or make-promise to specify the name, or remove to remove this procedure altogether.

Gleckler
Names that include the word "promise" are clearer. I prefer make-promise' to promise' because, in other make-foo' vs. foo' cases, e.g. for lists, strings, and vectors, the `foo' name has been used for multiple arguments of the same type.
Medernach
This wording is a lot better.
Shinn
I suspect people voted this in under the false impression it formed a pair of some sort with lazy. The utility is minor so I'd just as soon leave it out, but if we do keep it I'd prefer a self-explanatory name.
SnellPym
I've never felt the need for this anyway.

#308 Allow circular lists in LIST-REF for SRFI-1 compatibility

Allow the argument of list-ref to be circular. It is still an error to use an index >= the length of the list. None of my test implementations has a problem with this.

Vote circular to explicitly allow circular lists, error to add an "is an error" disclaimer, or unspecified to leave as is.

Cowan
A de-facto standard - every implementation allows this anyway.
Ganz
Shouldn't be explicitly allowed unless also allowed for index >= length of list. Making it an error would require performing that check.
Gleckler
This is what implementations already do. We should certainly not make it an error, so the second choice is clearly "unspecified."
Shinn
A de-facto standard - every implementation allows this anyway.

#309 Allow circular lists in MAP and FOR-EACH for SRFI-1 compatibility

Allow circular lists as the list arguments to map and for-each. If all arguments are circular, these procedures will not terminate unless the mapping procedure forces a non-local exit. The result of map is not circular. Implementations that stop when the shortest list runs out and don't make gratuitous tests shouldn't have a problem with this: R5RS allows, R6RS forbids, and R7RS requires this behavior.

Vote circular to explicitly allow circular lists, error to add an "is an error" disclaimer, or unspecified to leave as is. Unspecified leaves open the theoretical extension of returning a new circular list with the corresponding mapped results.

Cowan
The draft R7RS semantics makes this obvious.
Gleckler
This is useful, cheap, and matches R5RS. I've used an approach like this, for example, when constructing HTML with alternating colors for rows in a table.
Shinn
The draft R7RS semantics makes this obvious.

#310 Rationalize start/end/(fill) arguments in sequence procedures

When we approved CompleteSequenceCowan in ticket #64, we adopted SRFI 43 syntax and semantics for vector-copy, meaning that it takes optional start, end, fill arguments. This is inconsistent with various other copier procedures in R7RS as inherited from R5RS, as well as what is provided in SRFI 43 and its relatives SRFI 1 (for lists) and SRFI 13 (for strings). There are four plausible courses of action:

Cowan
Simpler is better in the core - people can always competing SRFIs and utility libraries.
Gleckler
This isn't expensive for implementations to provide, and there's widespread agreement on what it means. Let's have complete consistency and full power.
Hsu
The fill arguments are optional and do not make the language more complicated to use, and implementation is not difficult. It increases greatly the usefulness of these functions.
Shinn
Simpler is better in the core - people can always competing SRFIs and utility libraries.
SnellPym
I think they are relatively minor additions in terms of standard library code bloat, compared to the code bloat of reimplementing them all to provide the extra functionality *in an extra library on top of the core versions*.

#311 Remove tail call guarantee for guard clauses

The current draft guarantees the guard clauses (not the body) of a guard form to be in tail call position, but the need for this is unclear (who needs an unbounded number of active exceptions), and there may be worthwhile guard implementations where this is not the case.

Gleckler
I don't have a strong opinion here, but I buy the argument from lack of need for an unbounded number of active exceptions.
Hsu
We should not eliminate a good condition like this based on an assumption of the common use case of GUARD. Keeping the tail call guarantee makes GUARD more generally useful, though perhaps marginally so.
Shinn
A minor detail, but I think mentioning detracts more than it adds from the standard.

#312 unquoting and identifiers beginning with @

The current draft allows @ to begin an identifier, which would require some comment about unquoting, i.e. to distinguish whether ,@foo is (unquote @foo) or (unquote-splicing foo).

The options are invalid (disallow @ at the beginning of an identifier, as in R5RS), unquote to indicate that ,@foo is (unquote @foo), and unquote-splicing to indicate that ,@foo is (unquote-splicing foo).

If unquote-splicing is chosen, a note will be added saying that if you want to unquote an identifier beginning with @ you need to either insert whitespace or escape the identifier, e.g. either , @foo or ,|@foo|.

Note that if we don't choose invalid then SXML retroactively becomes valid syntax.

Cowan
This is what all implementations I'm aware of do - unquote would be strange and difficult semantics and is not completely speficied here, while invalid is undesirable due to SXML.
Gleckler
Anything other than invalid would be too confusing. If we're not going to do that, let's do what implementations already do, which is the unquote-splicing option.
Hsu
The unquote-splicing form more naturally maps to the way that people will have been used to seeing this. That is, if I have a ,@foo without @foo being defined anywhere, I expect to get (unquote-splicing foo) and not , @foo which will give me an error. This stuff is likely to happen before we get to anything that tells us whether an identifier is bound or not, and so this will be confusing for thos who do not use @foo identifiers. Those who do can easily get the behaviour they want, and they are more likely to know what is going on.
Shinn
This is what all implementations I'm aware of do - unquote would be strange and difficult semantics and is not completely speficied here, while invalid is undesirable due to SXML.
SnellPym
I think that the syntactic sugar 'operators' should have higher precedence than symbol syntax, as it's easier to quote a funny symbol than to write out (unquote-splicing ...) by hand.

#315 null character may not be usable in strings

We should probably make (string-set! str n #\null) unspecified. Note that R7RS implementations can already restrict the set of characters that are allowed in strings.

Vote yes to add a clause to this effect, and no to leave it as legal.

Cowan
R7RS implementations can already restrict the set of string-chars. I don't see any reason to call out null specially. If your implementation doesn't want to allow it, then don't allow it.
Gleckler
Since implementations can already prohibit #\null in strings, there's no need to do this. But the broken semantics of C strings shouldn't become part of the Scheme standard.
Medernach
I see no reason why scheme strings may or may not include #\null in some implementations, but if not you are free to disallow it.
Shinn
Many implementations can represent the null char, and at the same time use C strings as the underlying string representation, which makes this unspecified.
SnellPym
Not that I have any love for the null character, but I don't see a good reason to disallow implementations from supporting it if they want to. Somebody might wish to use Scheme to write test suites for string-processing tools, protocols, etc that might not be as null-transparent as they should be, so generating and examining test strings with nulls in would be a required feature then.

#316 R6RS base compatibility: boolean=?

This is equivalent to eq? on booleans, and provides R6RS base compatibility as well as completing the set of type-specific comparisons. See also #285.

Vote yes to add these three procedures.

Cowan
As in #285, this helps with type-inference.
Gleckler
It's good to complete the set of type-specific comparisons.
Shinn
As in #285, this helps with type-inference.
SnellPym
COnsistency is good.

#317 escape from with-input-from-file

The draft states for with-input-from-file and with-output-to-file:

If an escape procedure is used to escape from the continuation of these procedures, their behavior is implementation-dependent.

but now that we have dynamic-wind there's no particular reason to keep this restriction, nor is it difficult to implement.

Vote parameterize to specify the current-in/output-port are bound dynamically as with parameterize in these cases, or unspecified to leave unspecified.

Cowan
This was just an oversight, and was pretty clearly an oversight in R5RS which already had dynamic-wind.
Gleckler
This seems completely natural. I can't think of a reason that the behavior of these should be different than if they had been defined explicitly in terms of `parameterize'.
Shinn
This was pretty clearly an oversight in R5RS which already had dynamic-wind.

#319 Make special treatment of CAPITAL SIGMA optional

Currently we require that if the characters GREEK LETTER CAPITAL SIGMA, SMALL SIGMA, and SMALL FINAL SIGMA are supported by an implementation, that a CAPITAL SIGMA in a string passed to string-downcase be changed to SMALL FINAL SIGMA just before a word break, and SMALL SIGMA otherwise. Word breaks are defined by UAX #29, and are no simple matter. The proposal is to make this behavior optional, allowing CAPITAL SIGMA to be downcased to SMALL SIGMA in every case.

Vote yes to make optional.

Cowan
Alex says: "There are other complexities in case folding, I don't see why we should single out just this case." On the contrary, the rest of case folding for strings is trivial: there are 1027 characters to replace with another character, 88 characters to replace with a sequence of two characters, and 16 characters to replace with a sequence of three characters, all independent of the context. This can be executed in a single loop. By contrast, case-folding CAPITAL SIGMA requires determining whether a word-break follows: it cannot be done without look-ahead. To implement the word-breaking algorithm, one must keep around 13 character classes and implement 17 rules, all to get one character right -- and not even completely reliably: "φιλοσ." is right if t...
Gleckler
If John's argument that case folding sigma is AI-complete is even partially correct, then this makes sense. Furthermore, it is strange to incorporate this kind of language-specific Unicode-ism into the standard.
Shinn
I think this needs more discussion, but if we're defining string-*case in terms of an AI-complete word-break operator then that's the real problem, not what to do with sigma.
SnellPym
I know the full Unicode rules are complex, but if we don't support them properly, then it'll be difficult for users to get hold of full Unicode semantics when they need them - they'll have to implement it from scratch. Which means that, in effect, string-downcase is unreliable and can't be trusted and you have to use your own implementation if you care.

#320 Add new cond-expand feature to Appendix B: exact-complex

(In this ticket, "complex" is used for readability; it is synonymous with "non-real".)

This feature is true in implementations that support complex numbers such that both the real and the imaginary parts are exact; that is, if (eqv? 3+4i 3.0+4.0i) evaluates to #f. This feature is false if complex numbers are not supported or if only inexact complex numbers are supported. Most of the applications of complex numbers use inexact numbers, but some applications may require exactness: this feature allows those applications to fail fast on implementations that cannot support them.

Existing implementations:

Vote yes to add this feature.

Gleckler
Feature identifiers are cheap and useful.
Shinn
This is handy - it is already being used in the Chibi codebase.
SnellPym
Failing fast is what cond-expand is for, so let's give it the tools to do the job.

#321 Add get-features from EnvironmentEnquiriesCowan to R7RS-small

This procedure returns a list of symbols corresponding to the feature identifiers which the implementation treats as true. More details at EnvironmentEnquiriesCowan.

Vote yes to add this procedure.

Cowan
This can be useful for debugging and version info.
Gleckler
I'd like to be able to print the list of features on start-up, for example. This information will certainly be available to the implementation, so it should be made available programmatically. However, this should be called features' or feature-list', not `get-features'. The latter sounds like Java.
Shinn
This can be useful for debugging and version info.
SnellPym
This is useful, but I have a hunch it shouldn't be required as it might be an expensive operation to do on systems that dynamically load features on demand etc.

#322 Add EnvironmentEnquiriesCowan (other than get-features) to R7RS-small

EnvironmentEnquiriesCowan is a library providing at run time what Common Lisp calls environment enquiries such as the name of the OS. Implementations can currently expose these as cond-expand feature identifiers, but there is no way to determine things like the name of the implementation at run time so that it can be written to a log file, for example.

Vote yes to add EnvironmentEnquiriesCowan (other than get-features), and no to leave out.

Cowan
This needs more use and investigation, and as a library has no advantage being in the small language (as opposed to features). Let's add this to the large language.
Ganz
Seems good to have.
Gleckler
This information is easy and cheap for any implementation to provide inexpensively, and is highly useful. However, implementation-type' should be called implementation-name'. After all, the description at EnvironmentEnquiriesCowan starts "Returns the name [not the type] of the Scheme implementation."
Shinn
This needs more use and investigation, and as a library has no advantage being in the small language (as opposed to features). Let's add this to the large language.
SnellPym
My answer to the previous nonwithstanding, it's good to be able to provide information that the implementation should generally have trivial access to.

#323 Eliminate some cond-expand feature identifiers

Reduce the standardized cond-expand feature identifiers to r7rs, exact-closed, ratios, ieee-float, and full-unicode, plus the name and name-plus-version of the implementation. The others can't affect the behavior of strictly conforming programs, and it's not clear if they apply to compile time or run time on implementations that distinguish the two. See also ticket #320 for exact-complex.

Argument against: Keeping them in the standard encourages all implementations that use them to spell them the same way: darwin, not macosx.

Vote full to keep the full list as in draft-6, implementation to keep only the implementation features, or numerics to keep the list described above.

Cowan
Pending a better list, I think many of the features are useful, and are actively in use in several implementations.
Gleckler
The list is useful. The argument that the other features identifiers can't affect the behavior of strictly conforming programs misses the point. The whole point of those identifiers is dealing with places where implementations differ.
Shinn
Pending a better list, I think many of the features are useful, and are actively in use in several implementations.

#259 Remove (library <name>) cond-expand features

The (library <name>) feature test which is true if the given library is available (at compile time). This was used because we voted for CondExpandCowan, but the original syntax was just <name> which is ambiguous and therefore invalid. The switch to (library <name>) was added editorially, but not officially voted on.

Vote keep to keep and remove to remove.

Cowan
I personally don't care if users are forbidden to name libraries (not ...), (and ...), or (or ...), but this is a sensible way to avoid a minor problem.
Gleckler
This avoids ambiguity. Clashes are unlikely, but that's exactly what makes debugging them difficult when they do happen. This avoids the problem entirely.
Shinn
A formality - we basically already voted this in.

#324 allow |\ as escape for | within a |-escaped identifier

Allow \| to represent a vertical bar in an identifier enclosed in vertical bars (the current BNF disallows | anywhere in the escape).

Note this item is nullified if |...| escapes are removed in item #304.

Vote pipe to allow just the vertical bar escaped, string to allow the same set of escapes as in string literals (plus pipe), and none to leave as is.

Cowan
I think this was an oversight.
Gleckler
Consistency makes things easier to remember, and there's no reason not to be consistent with strings here.
Hsu
this defeats the purpose of |...| in my opinion.
Shinn
I think this was an oversight.

#325 Eliminate bytevector-copy!

(bytevector-copy! from to) is equivalent to (bytevector-copy-partial! from 0 (bytevector-length) to 0).

The proposal is to remove the existing bytevector-copy! from the small language, and rename bytevector-copy-partial! to bytevector-copy!, with the order of arguments `to at from start end, the same order used in SRFI 43's vector-copy!`. Note that SRFI 43 will be part of the large language.

Vote yes to eliminate and rename as proposed, and no to leave as-is.

Cowan
There were many complaints against the existing API, we should simplify this.
Gleckler
Yes, let's make this consistent.
Shinn
There were many complaints against the existing API, we should simplify this.

#326 Add destructive list-copy!, string-copy!, and vector-copy!

From Per Bothner:

Copying a slice from one vector/string into another is such a fundamental operation that it should be added, IMO, considering that it's tedious to write if "by hand", and that a standard library routine is likely to be much more efficient (especially for strings, since that avoids the need for boxing and unboxing the characters). [JC: Many implementations represent characters as immediates, however.]

One could also argue that "character" operations don't really make semantic sense in a Unicode world, and so string-set! has limited usefulness. Thus string-copy [with start/end arguments] and string-copy! are the actual useful "primitive" operations.

JC: These would be the five-argument versions based on the current bytevector-copy-partial!, possibly with renumbering of arguments depending on the outcome of #325.

Vote yes to add these destructive operations as proposed, nolist to add string-copy! and vector-copy! only, or no for none of them.

Cowan
I added list-copy! to this ballot for uniformity, but on reflection I agree that it's not that useful, whereas string-copy! and vector-copy! are.
Gleckler
I agree with others' comments about list-copy!. However, string-copy! and vector-copy! are quite useful and cheap.
Shinn
list-copy! is very rarely used and usually indicative of a broken algorithm. string-copy! is a step away from immutable strings, and terrible performance for utf8 implementations. vector-copy! is more useful but probably better left to a general vector library, though I could be convinced to include just it.
SnellPym
I want cons cells and strings, to be less mutable, but am open to mutability in vectors.

#327 Specify that read, the program reader, and string->number accept the same syntax

Currently there is no guarantee of this. Obviously the string->number only applies to the case where the radix is 10 or specified.

Specifying same is problematic in the presence of batch compilation

tower.

Cowan
Basically all we can and should say is that string->number with a radix of 10 should behave the same as read.
Ganz
Programs can be data.
Gleckler
I don't understand why we should support having different numerics tower at compile time and run time. That seems like a recipe for confusion. What implementations make this distinction?
Shinn
Basically all we can and should say is that string->number with a radix of 10 should behave the same as read.
SnellPym
Implementations having different numeric towers and compile and run time, I feel, is already a recipe for pain and suffering, so effort spent pandering to it is probably not well spent!

#328 names for inexact->exact and exact->inexact

R6RS changed these names to the more sensible exact and inexact. We need to decide if we want to follow suit, or provide both names, or write a disclaimer.

Vote r6rs for the short names, r5rs for the long names, or both for both.

Cowan
We have a library system now, we shouldn't be too afraid to clean up names. The (scheme r5rs) library can be voted in if we want easy 100% compatibility.
Ganz
The long names seem more consistent with other function names.
Gleckler
It's pointless and confusing to have both.
Lucier
Actually, I'd prefer ->exact and ->inexact.
Medernach
I like the long names as it shows clearly that it is conversion procedures. Ok, this is kind of bike-shedding.
Shinn
We have a library system now, we shouldn't be too afraid to clean up names. The (scheme r5rs) library can be voted in if we want easy 100% compatibility.
SnellPym
I prefer the R6RS names.

#329 Add IEEE compatibility library

The (scheme ieee) library exports the standard identifiers of IEEE 1178-1990. By my current reckoning, those identifiers are as follows:

`- * / + < <= = > >= abs acos and angle append apply asin assoc assq assv atan begin boolean? call-with-current-continuation car case cdr ceiling char->integer char-alphabetic? char-ci<? char-ci<=? char-ci=? char-ci>? char-ci>=? char-downcase char-lower-case? char-numeric? char-upcase char-upper-case? char-whitespace? char? char<? char<=? char=? char>? char>=? close-input-port close-output-port complex? cond cons cos current-input-port current-output-port define denominator display do eof-object? eq? equal? eqv? even? exact->inexact exact? exp expt floor for-each gcd if imag-part inexact->exact inexact? input-port? integer->char integer? lambda lcm length let let* letrec list list-ref list? log magnitude make-polar make-rectangular make-string make-vector map max member memq memv min modulo negative? newline not null? number->string number? numerator odd? open-input-file open-output-file or output-port? pair? peek-char positive? procedure? quasiquote quote quotient rational? rationalize read read-char real-part real? remainder reverse round set-car! set-cdr! set! sin sqrt string string->number string->symbol string-append string-ci<? string-ci<=? string-ci=? string-ci>? string-ci>=? string-length string-ref string-set! string? string<? string<=? string=? string>? string>=? substring symbol->string symbol? tan truncate vector vector-length vector-ref vector-set! vector? write write-char zero?`

As with any library other than (scheme base), implementations SHOULD (rather than MUST) provide this.

Vote yes to add this library.

Cowan
It's easier to provide (scheme r5rs).
Gleckler
People don't care much about IEEE Scheme, so we shouldn't force implementations to provide this.
Shinn
I don't think people would ever want to use this instead of (scheme r5rs).

#330 Add R5RS compatibility library

The (scheme r5rs) library exports the standard identifiers of R5RS Scheme other than transcript-{on,off}. By my current reckoning, those identifiers are as follows:

`- * / + < <= = > >= abs acos and angle append apply asin assoc assq assv atan begin boolean? call-with-current-continuation call-with-values car case cdr ceiling char->integer char-alphabetic? char-ci<? char-ci<=? char-ci=? char-ci>? char-ci>=? char-downcase char-lower-case? char-numeric? char-ready? char-upcase char-upper-case? char-whitespace? char? char<? char<=? char=? char>? char>=? close-input-port close-output-port complex? cond cons cos current-input-port current-output-port define define-syntax delay denominator display do dynamic-wind eof-object? eq? equal? eqv? eval even? exact->inexact exact? exp expt floor for-each force gcd if imag-part inexact->exact inexact? input-port? integer->char integer? interaction-environment lambda lcm length let let-syntax let* letrec letrec-syntax list list->string list->vector list-ref list-tail list? load log magnitude make-polar make-rectangular make-string make-vector map max member memq memv min modulo negative? newline not null-environment null? number->string number? numerator odd? open-input-file open-output-file or output-port? pair? peek-char positive? procedure? quasiquote quote quotient rational? rationalize read read-char real-part real? remainder reverse round scheme-report-environment set-car! set-cdr! set! sin sqrt string string->list string->number string->symbol string-append string-ci<? string-ci<=? string-ci=? string-ci>? string-ci>=? string-copy string-fill! string-length string-ref string-set! string? string<? string<=? string=? string>? string>=? substring symbol->string symbol? tan truncate values vector vector->list vector-fill! vector-length vector-ref vector-set! vector? with-input-from-file with-output-to-file write write-char zero?`

As with any library other than (scheme base), implementations SHOULD (rather than MUST) provide this. A disclaimer will be added that the semantics may not be exactly the same.

Vote yes to add this library.

Gleckler
This will make using old programs easier.
Medernach
For compatibility
Shinn
This eases backwards-compatibility greatly.

#331 Add R6RS base compatibility library

The (scheme r6rs base) library exports the standard identifiers of the base library of R6RS. By my current reckoning, those identifiers are as follows:

`- * / + < <= = > >= abs acos and angle append apply asin atan begin boolean? call/cc call-with-current-continuation call-with-values car case cdr ceiling char? char<? char<=? char=? char>? char>=? char->integer complex? cond cons cos define define-syntax denominator dynamic-wind eq? equal? eqv? even? exact exact? exact-integer-sqrt exp expt finite? floor for-each gcd guard if imag-part import inexact inexact? integer? integer->char lambda lcm length let let* let*-values letrec letrec* letrec-syntax let-syntax let-values list list? list->string list->vector list-ref list-tail log magnitude make-polar make-rectangular make-string make-vector map max min nan? negative? not null? number? number->string numerator odd? or pair? positive? procedure? quasiquote quote rational? rationalize real? real-part reverse round set! sin sqrt string string? string<? string<=? string=? string>? string>=? string->list string->number string->symbol string-append string-copy string-for-each string-length string-ref substring symbol? symbol->string tan truncate values vector vector? vector->list vector-fill! vector-for-each vector-length vector-map vector-ref vector-set! zero?`

As with any library other than (scheme base), implementations SHOULD (rather than MUST) provide this. Full compliance will depend on voting for the procedures *-valued, assert, boolean=?, symbol=?. A disclaimer will be added that the semantics will not be exactly the same.

Vote yes to add this library.

Gleckler
This might be reasonable for large Scheme, but one of the points of small Scheme is to avoid having to support R6RS.
Medernach
Really it makes no sense to provide all of this in WG1, but may be provided in WG2
Shinn
I don't agree with including all of the R6RS base exports in the small language, and the small language has no obligation to support R6RS - that's the reason we have a large language.

#332 Allow multiple name pairs in export renaming

Currently, to export my:foo and my:bar as foo and bar, one must write (export (rename my:foo foo) (rename my:bar bar)). This proposal allows (export (rename (my:foo foo) (my:bar bar))). This is incompatible with R6RS, but compatible with the rename sub-form of import.

Vote multiple to allow multiple renames in one rename clause as with the import version, r6rs to allow the R6RS-compatible syntax in the current draft, or both to allow both forms.

Gleckler
Why not be compatible with `rename'?
Shinn
I like the simplicity of (length export-list) indicating the number of exports.
SnellPym
Consistency with import strikes me as preferable.

#333 Require eof-objects to be disjoint from basic Scheme types

It's already a requirement that an eof-object cannot have an external representation, which means it cannot be any of the basic types in Section 3.2 except procedure or port. This is very improbable, and in fact none of my 40 test Schemes returns either a procedure or a port.

Doing this would allow eof-object? to be added to the list of disjoint type predicates in Section 3.2.

Vote yes to explicitly list the eof-object as a separate disjoint type.

Gleckler
Now that #f and '() are of distinct, we've been moving toward disjoint types in general.
Shinn
This is a useful guarantee and a de-facto standard.

#334 Use proper case for the feature identifiers in Appendix B

Specifically R7RS, IEEE-float, full-Unicode, Windows, POSIX, Unix, Darwin, Linux, BSD, FreeBSD, Solaris, PPC, SPARC, JVM, CLR, LLVM, ILP32, LP64, ILP64.

Note this is incompatible with existing implementations which provide these features. The correct case can often be ambiguous, and it's easiest to keep everything consistently lower case.

Vote mixed for mixed case and lower for lower case.

Cowan
We have enough of a de-facto standard with existing implementation features, and as a general rule I hate mixed-case identifiers. People are inconsistent as to when they use it in different libraries (is it "utf8" or "UTF8"?, etc.), so it's easier to remember if everything is lowercase. It also saves having to touch the shift key.
Gleckler
While this was my proposal, I'm voting against it based on the argument that some of these feature identifiers are already being used in lower case. It feels illiterate to require case sensitivity but then demand that people use case that doesn't match the natural-language names, but since feature identifiers exist for purely practical purposes, we're struck with this.
Shinn
We have enough of a de-facto standard with existing implementation features, and as a general rule I hate mixed-case identifiers. People are inconsistent as to when they use it in different libraries (is it "utf8" or "UTF8"?, etc.), so it's easier to remember if everything is lowercase. It also saves having to touch the shift key.

#335 Specify behavior of default exception handler

If an exception is caught and leaves the current dynamic extent, obviously the after thunk must be run, but an uncaught exception has no semantics and is basically reverting to "is an error" semantics,

  1. e. nasal demon territory.

Possibly we should tighten this up in the standard, i.e. specify that there is a default exception handler which enters a continuation outside the extent of the whole program before exiting.

Vote unwind to specify that there is a default exception handler which leaves the current dynamic extent causing a full unwind (and thus forbidding a debugger), exit to specify that (modulo any diagnostic information) the program must simply exit without unwinding, or unspecified to leave this as is.

Cowan
The default behavior in some existing implementations such as Gambit is to drop into a debugger, even in a batch program, so I don't think we can specify this.
Ganz
The semantics of the inner block should not be dependent on what happens outside afterwards.
Gleckler
Implementations vary too much in this regard, and it's an area where the context of the program and implementation matter a lot, so we should leave it up the implementers.
Shinn
The default behavior in some existing implementations such as Gambit is to drop into a debugger, even in a batch program, so I don't think we can specify this.
SnellPym
unwind doesn't forbid a debugger, but merely makes it non-compliant. However, as a feature one turns on in an implementation by requesting it, it would be a perfectly valid and useful noncompliance. After all, other debugging facilities, such as randomly changing mutable state at any point in program execution, are clearly also in violation of the spec. It's disappointing if dynamic-wind is unreliable.

#344 Should dynamic-wind handlers be invoked from EXIT?

Currently the report is silent about whether dynamic-wind handlers are invoked when exit is called.

The options are the same as in #335 above.

Cowan
Contrary to #335 above, there is no reason not to unwind here. Once finalizers are supported (maybe in the large language) we'd probably want to require them to be run as well. Note this does mean that exit can't be a simple wrapper around the syscall.
Ganz
Like the name says. At least there should be some function that does this; it could be called 'abort'. But it must be specified.
Gleckler
I'm uncomfortable specifying what should be done here without knowing what existing implementations do in general. For some people, `exit' means "get out of here immediately." I don't want something that happens in a dynamic-wind handler to prevent the program from exiting, for example, or to delay exit.
Shinn
Contrary to #335 above, there is no reason not to unwind here. Once finalizers are supported (maybe in the large language) we'd probably want to require them to be run as well. Note this does mean that exit can't be a simple wrapper around the syscall.
SnellPym
Likewise.

#337 Add eof-object procedure

eof-object returns an object which answers #t to eof-object?. This procedure is present in R6RS, where it must return the unique end-of-file object; that is not required here.

From Vincent Manis:

This isn't just an attempt to create a vain orthogonality; there are good reasons why arbitrary code might wish to return an eof object. For example, a DBMS interface might have a routine that returns one row, as a list or a vector, at a time; after the last, it is perfectly reasonable to return an eof object.

An argument against providing this is that the constructor may be trivially written, as shown [below]. A similar argument could be applied to zero?, newline, quotient, remainder, and modulo, among others. R7RS is not afraid to provide easy-to-implement procedures in the name of simplicity, orthogonality, or historical compatibility. The lack of an eof constructor is worth remedying.

(let* ((p (open-input-string "")) (x (read p))) (close-port p) x)

Vote eof-object for a procedure of that name, or none to not add any such procedure.

Cowan
I end up generating this often enough anyway with (read-char (open-input-string "")).
Ganz
Why isn't this 'make-eof-object'?
Gleckler
I don't buy Vincent's argument from the DBMS example. After all, a DBMS is not a file, so returning an end-of-file object is a strange choice. #f or '() would be equally valid. However, people do seem to create EOF objects for file-related purposes, so why not make it easy to construct them in a non-klugerous way?
Shinn
I end up generating this often enough anyway with (read-char (open-input-string "")).

#339 Restrict identifiers in library names for compatibility with file system restrictions

Currently the identifiers in library names can be any identifier. Under this proposal, the identifiers must not include any of `| \ ?* < " : > + [ ] /` or control characters after escapes are expanded.

If this proposal fails, its content will be included non-normatively as a should not.

Vote yes to restrict with must not.

Cowan
R6RS had enough headaches with this and ":", we should avoid the same mistake.
Ganz
'Should not' is sufficient.
Gleckler
Operating-system level naming concerns shouldn't be pushed up to the library level. After all, some R7RS small implementations won't have a file system at all.
Shinn
R6RS had enough headaches with this and ":", we should avoid the same mistake.

#340 Include non-normative note about the file-system based implementations of libraries

Libraries do not necessarily have any mapping to files, nor does an implementation necessarily run on a system with a filesystem, however for those implementations which do so it may be worth adding such a note.

A library file contains a single library. A library named (A1 A2 AN) is in a file named "A1/A2/AN.sld" ("sld" for "Scheme Library Definition" or some other standardized file extension), relative to some "library path". For portability, library component names should be integers or lower-case identifiers that avoid certain prohibited characters. When a library or top-level imports some other library, the corresponding file is found in the obvious way.

Alternately, this can be left entirely to WG2 and/or packaging systems such as Snow.

Vote yes to add such a note or no to leave it out.

Cowan
This belongs in Snow.
Gleckler
We shouldn't constrain files to contain only single libraries. Good Scheme code includes lots of small procedures and macros, and small libraries will be common, too. Forcing each into a separate file unnecessarily constrains the programmer's ability to keep similar concepts grouped naturally.
Shinn
This belongs in Snow.
SnellPym
It will help portability.

#341 Permit ambiguous imports of identifiers which are never used

It is currently an error to attempt to import the same identifier from more than one library into another library or a top-level program, even if the identifier is not used anywhere in the new library or program. That requires programmers to make an arbitrary decision to exclude it from one library or the other.

Vote yes to agree with this proposal to require that, within a single static library (not with the environment procedure where any identifier may be subsequently used), an implementation must allow such multiple imports if the identifier is not referenced and does not occur in a syntax-rules template (which introduces conflicts with low-level macros introduced by WG2).

Cowan
Overall I think this is more of a pain than it's worth.
Gleckler
It's better for programmers to address the possible conflict explicitly.
Medernach
What is important is that references are non ambiguous, there are no risks if unused identifiers collide. If an identifier with multiple meanings is not used, there is no ambiguity, nor real conflict.
Shinn
I think this is too difficult to specify and implement.
SnellPym
This sounds too complex a rule for it to be a good idea, surely?

#342 Have READ-BYTEVECTOR(!) return 0 at EOF

Currently, read-bytevector and read-bytevector! return an EOF object at EOF; otherwise, read-bytevector returns a non-empty bytevector and read-bytevector! returns the number of bytes read. Returning #u8() and 0, respectively, at EOF instead would make the results always the same type. This change would introduce the ambiguity that one would not be able to detect EOF when reading a bytevector of length 0 (which is to say, not reading any bytes at all).

Vote zero to return #u8() and 0 as in the proposal, and eof-object to return the eof-object as in the current draft. Vote zero! to make the change only for read-bytevector!.

Cowan
Returning the eof-object as in the current draft is ubambiguous and consistent with R6RS.
Gleckler
Returning an EOF object allows one to distinguish the zero-byte case, which is inmportant.
Medernach
Reading nothing is not the same as stopping reading.
Shinn
Returning the eof-object as in the current draft is ubambiguous and consistent with R6RS.
SnellPym
Sentinel values should be very obviously distinct, to help avoid accidents.

#343 Editorial: divide domain explanations to be split before and after descriptions

All Scheme standards up to and including R6RS and R7RS draft-6 have consistently placed the full domain at the beginning of each entry. In most cases the domain consists only of the implicit type restrictions from the prototype, but in some cases there are additional domain restrictions that cannot be conveniently included in the prototype such as the following map restrictions:

It is an error if proc does not accept as many arguments as there are lists and return a single value.

It has been suggested to move this to an appropriate later point in the entry, to put more emphasis on the initial entry description. This has the disadvantage of splitting the domain into two places, which can more easily cause oversights and make quick domain confirmations difficult.

An alternative is to separate the additional domain restrictions from the initial description, as a separate short paragraph immediately following the prototype and possibly de-emphasized by making it smaller. his would keep the domain in one place and still allow let the first line of the description stand out prominently in the initial paragraph.

Vote start for the status quo, start-split for the separate de-emphasized option, or later to move additional restrictions to a later point.

Cowan
I want to keep all domain information in a single place - I often know what a procedure does but need to double check only the domain, and having to jump around to find it is inconvenient.
Gleckler
Start-split is a nice compromise.
Shinn
I want to keep all domain information in a single place - I often know what a procedure does but need to double check only the domain, and having to jump around to find it is inconvenient.
SnellPym
The extra conditions tend to be "edge cases" anyway, that would deserve a thorough reading of the whole thing before dabbling with!

#345 Should 0.0 and -0.0 be distinct in the sense of EQV?

Currently, the draft report implies that 0.0 and -0.0 must be the same in the sense of eqv?, because eqv? defers to = for numbers (with the possible exception of NaNs).

Vote same for the status quo, different to change to "must be different", or unspecified to change to "may be different".

Cowan
We should neither require nor forbid implementations from distinguishing -0.0.
Gleckler
Unless we know that most implementations have chosen to do the same thing in this case, we should leave it unspecified.
Lucier
If there are any Schemes with non-IEEE arithmetic, then this should be unspecified.
Shinn
This should fall out naturally from the definition of eqv?, which currently makes it clear that they must be the same, though we'll be revisiting this.

#349 Define exact integers to be at least 24 bits

Currently, R7RS (tracking R5RS) does not constrain the sizes of exact integers beyond being required to represent the indices of strings, vectors and bytevectors.

R6RS requires systems to support "practically unlimited" size exact integers. It also requires that a subset of these exist, called fixnums, which must support at least the range -223 to 223-1. (All practical Schemes have larger ranges for their fixnums). This proposal suggests that we adopt this range as the minimum range of R7RS exact integers.

The immediate issue here is that a library name may contain (non-negative) exact integers as well as identifiers in R7RS. For such names to be portable, there must be a portable range of exact integers.

See FixnumInfo to see what 39 existing Schemes do.

Vote 24 to require 24 bits of precision, 16 to require 16 bits of precision, or none to leave this entirely unspecified.

Cowan
Alex says: "R7RS small does not make the ugly 'fixnum' distinction, and I don't see why we should set such arbitrary minimums, or forbid simplistic Scheme implementations on 16-bit machines." All very well, but as long as we allow numbers in module names (basically introduced for the sake of SRFIs), we need to say something about the portability of such values.
Gleckler
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.
Medernach
Integers in library names are often used as a practical solution to manage dependencies (even if this is not completely satisfactory IMHO). We should have at least be safe to make comparisons between versions, so a portable range is necessary.
Shinn
R7RS small does not make the ugly "fixnum" distinction, and I don't see why we should set such arbitrary minimums, or forbid simplistic Scheme implementations on 16-bit machines.

#354 mutating exports

We define mutating imports to be an error, however the standard currently says nothing about what happens when an exported binding is mutated from within the library where it's defined. In many common library implementations there will be no effect (i.e. the import effectively gets a copy of the original), whereas in a namespace based implementation the change will be reflected, so a conservative approach is to add a note saying the result is unspecified.

Vote shared to force the binding to be shared and the change reflected everywhere it's imported, separate to force the binding to be separate, none to make no comment, and unspecified or error to add a clarification to the standard to that effect.

Cowan
This was the original intention, and leaving it out was an oversight.
Ganz
I don't see any use for separate bindings, other than potential convenience of implementation.
Gleckler
I vote "shared" because a library should be able to mutate its own binding, particularly when the programmer is making changes in a REPL. In addition, "shared" makes importing libraries behave as if they had closed over the binding that will be mutated the way that closures do over lexically enclosing bindings. It's easy to share a cell to make this work.
Hsu
It should be an error that an implementation try to export an assigned variable. This should happen at the time of the library definition IMO.
Shinn
This was the original intention, and leaving it out was an oversight.

#358 change epoch of current-second

A formal comment has proposed changing the epoch of current-second to 1970-01-01 00:00:00 TAI rather than 1970-01-01 00:00:10 TAI (00:00:00 UTC).

The actual time systems are independent of an epoch - the epoch is just convenient for computer systems.

The UTC-centric epoch was chosen (despite the use of TAI time) mostly because it is used in popular TAI times such as libtai and Olson's time library.

See http://lists.scheme-reports.org/pipermail/scheme-reports/2012-March/001943.html for more details.

Vote utc for the current draft's start-of-1970-in-utc epoch, or tai for the proposed start-of-1970-in-tai epoch.

Cowan
I originally proposed TAI - 10, but on reflection I think people implementing this from scratch are less likely to get it wrong if it's based on TAI - UTC (34 seconds at present) rather than TAI - 10 - UTC (24 seconds).
Gleckler
If we're using TAI time, we should use the TAI epoch. The ten-second skew is just random, and leaving it in is just asking for errors in code that is already error-prone for other reasons.
Shinn
I actually haven't been able to find any libraries which use the TAI epoch.