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2012-07-15 02:15:54
1Added copy of fifth ballot.history


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:

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.

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.

#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.

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.

#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.

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," <>. 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 "definitional engineering" decisions down to wrong or erroneous definitions, as in the 1S0 Standard for Pascal [11, 13], Algol 68 [201, and some other languages.

In this paper we clarify the differences between the various definitions, in particular those based on division by truncation (T-definition) and on division by flooring (F-definition) as defined by Knuth [14]. We also propose still another definition, which we call Euclidean because it is based on Euclid’s theorem (E-definition). This alternative is rarely discussed in the literature, yet on closer analysis it is advantageous in terms of regularity and useful mathematical properties, both theoretically and in practical usage. The Euclidean definition usually emerged as the most straightforward choice, over a wide variety of representative application areas where we experienced the need for a div-mod function pair.

Comparison of the various definitions leads to a preference for the E- and F-definitions as the standard convention in mathematics and programming terms of the languages. Secondary definitions can always primary ones to cater for the exceptional cases.

At the computer architecture level, the preferred definitions most important number representation and computer arithmetic uniform way [5]. Although this suggests the possibility of simpler hardware realizations than for the other definitions, verifying this requires a thorough study in ALU design that is clearly beyond the scope of this paper. Difficulties such as the problem with arithmetic shifting pointed out by Steele [17] are also avoided.

The paper goes on to discuss various reasons that the Euclidean option is more practical, matches to the underlying hardware better, and works better in common applications.

Also, I don't buy the argument that only floor-* and truncate-* have an established history in computer programming and mathematics. Scheme has a history of pushing the envelope in mathematicaly computation, e.g. with exact arithmetic, and this fits with that tradition and is not expensive to programs that use the new operators nor to ones that don't.

Finally, Common Lisp supports the ceiling, floor, round, and truncate options. Why should we drop ceiling and round?

#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.

Alex assured us that this wouldn't make things like `#(1 ,(+ 2 3)) fail, so I'm voting yes.

#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.

This is too obvious to be worth specifying. Furthermore, if we specify it here, what are we implying about other procedures like 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).

This is an obvious choice for consistency of implementations that support Unicode.

#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.

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.

#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.

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.

#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.

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.

#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.

Sounds reasonable.

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.

I buy the argument from symmetry with `sqrt'.

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.

Yes, this error shouldn't happen silently. Since implementations already signal it, this change won't be a problem.

#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.

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.

#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.

The standard already makes this clear in a general way. There's no way to repeat that information for conditionals in particular.

#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.

Same argument as for #293: this is already clear, and repeating it would be redundant.

#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.

Same argument as for #293: this is already clear, and repeating it would be redundant.

#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.

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.

#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.

This name makes the purpose clearer.

#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.

As others have said, the |...| syntax is widely implemented. I don't think the backslash-only syntax is 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.

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?

#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.

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.

#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.

This is what implementations already do. We should certainly not make it an error, so the second choice is clearly "unspecified."

#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.

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.

#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:

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.

#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.

I don't have a strong opinion here, but I buy the argument from lack of need for an unbounded number of active exceptions.

#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.

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.

#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.

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.

#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.

It's good to complete the set of type-specific comparisons.

#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.

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'.

#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.

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.

#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.

Feature identifiers are cheap and useful.

#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.

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.

#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.

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."

#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.

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.

#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.

This avoids ambiguity. Clashes are unlikely, but that's exactly what makes debugging them difficult when they do happen. This avoids the problem entirely.

#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.

Consistency makes things easier to remember, and there's no reason not to be consistent with strings here.

#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.

Yes, let's make this consistent.

#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.

I agree with others' comments about list-copy!. However, string-copy! and vector-copy! are quite useful and cheap.

#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


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?

#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.

It's pointless and confusing to have both.

#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.

People don't care much about IEEE Scheme, so we shouldn't force implementations to provide this.

#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.

This will make using old programs easier.

#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.

This might be reasonable for large Scheme, but one of the points of small Scheme is to avoid having to support R6RS.

#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.

Why not be compatible with `rename'?

#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.

Now that #f and '() are of distinct, we've been moving toward disjoint types in general.

#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.

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.

#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.

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.

#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.

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.

#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.

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?

#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.

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.

#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.

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.

#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).

It's better for programmers to address the possible conflict explicitly.

#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!.

Returning an EOF object allows one to distinguish the zero-byte case, which is inmportant.

#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. [T]his would keep the domain in one place and still allow let [sic] 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.

Start-split is a nice compromise.

#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".

Unless we know that most implementations have chosen to do the same thing in this case, we should leave it unspecified.

#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.

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.

#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.

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.

#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 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.

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.