Earlier we voted on #125, #229 and #345 separately without regard to the formal semantics of eqv? from a top level. We need to first decide what the definition of eqv? is, and consider if there should be any exception cases as a secondary effect.
The debate is fundamentally one of whether we define eqv? in terms of "operational equivalence" as in R6RS or a simpler rule (e.g. resolve by =) as in earlier standards.
R2RS had the simplest historical rule which was simply to use =.
The term "operational equivalence" appears in R3RS but for numbers the definition is the same as in R4RS and R5RS, which is = plus the same exactness. This is the r5rs option, with the "true" cases written formally as:
The `eqv?` procedure returns #t if: (1) obj1 and obj2 are both booleans and are the same according to the `boolean=?` procedure. (2) obj1 and obj2 are both symbols and are the same symbol according to the `symbol=?` procedure. (3) obj1 and obj2 are both numbers, have the same exactness, are numerically equal (see `=`). (4) obj1 and obj2 are both characters and are the same character according to the `char=?` procedure. (5) obj1 and obj2 are both the empty list. (6) obj1 and obj2 are pairs, vectors, bytevectors, records, or strings that denote the same location in the store. (7) obj1 and obj2 are procedures whose location tags are equal.Note that (7) is an exception case which will be decided separately in #125. Furthermore, an exception to make NaNs unspecified regardless of the semantics here will be decided in #229.
The r6rs vote replaces (3) with the following operational equivalence semantics:
(3.1) obj1 and obj2 are both exact numbers and are numerically equal (see `=`) (3.2) obj1 and obj2 are both inexact numbers, are numerically equal (see `=`), and yield the same results (in the sense of `eqv?`) when passed as arguments to any other procedure that can be defined as a finite composition of Scheme’s standard arithmetic procedures.where "standard arithmetic procedures" refers arguably to either
section 6.2.6. R6RS further adds an extra case which is not applicable because we don't guarantee record-types are first-class objects:
(8) obj1 and obj2 are record-type descriptors that are specified to be `eqv?` in library section on “Procedural layer”.The r6rs/all option changes (3.2) to a finite composition of any of the implementations arithmetic procedures. The intention is that decode-float if provided could distinguish NaNs, but something like eq? (which could distinguish the same bit pattern in different locations) would not be considered arithmetic and not apply. This does leave the definition "arithmetic" open to some interpretation.
In contrast to R6RS, R7RS does not require the full numeric tower. This means that any definition of operational equivalence would render many numbers unspecified from the perspective of the standard, yet users could rely on consistency within their own implementation, and broad agreement amongst most implementations which provide the full tower.
Finally, the same-bits option replaces (3) with:
(3.1) obj1 and obj2 are both exact numbers and are numerically equal (see `=`) (3.2) obj1 and obj2 are both inexact real numbers conforming to the IEEE 754-2008 standard, and they have the same radix, precision, maximum exponent, sign, exponent, and significand as described in IEEE 754-2008 (3.3) obj1 and obj2 are both inexact real numbers, are not implemented using IEEE 754-2008, and are numerically equal (see `=`) (3.4) obj1 and obj2 are both complex numbers whose real and imaginary parts are `eqv?`Keep in mind the semantics of eqv? also affect memv, assv and case.
Rationale: I was impressed by Bradley's arguments that same-bits matches IEEE 754 and is therefore superior.
The R6RS semantics are defined too indirectly and are too dependent on the specific combination of numeric features supported by the implementation. The R5RS semantics are clearer.
I would argue for an option that is the same as r5rs but distinguishes between positive and negative zero in the same way as we already distinguish between exact and inexact, but that does not appear on the ballot.
I don't agree with choosing r6rs/all over r6rs. Implementation-specific procedures like decode-float, the example given above, are specifically designed to expose implementation details, whereas eqv? has generally been used to compare numbers arithmetically. If we add implementation-specific procedures to the requirement, the definition of eqv? becomes even more indirect, and adding a new procedure to an implementation may change the meaning of eqv? for existing code.
This whole debate illustrates the well-known futility of designing an equivalence predicate that works for everyone's purposes. Regardless of the outcome of this ballot, someone who wants reliable, portable control over exactly what numbers are considered equivalent will not be able to use eqv?.
By the way, I commend the authors of this ballot item. It has always been, through several rewrites, well written, and the references were particularly helpful.
As announced previously this is being re-opened due to incorrect formulation in the previous ballot, and in response to formal comment #423.
Regardless of the result of #460, the semantics implies that eqv? return #f on comparing any two NaN objects. It is reasonable to want to consider any two NaNs as the "same" since they behave the same under any operation, even though none of the results are =. Moreover, it is very common to use a shortcut eq? pointer comparison before falling back on general eqv? logic. In deference to this R6RS makes an exception and allows the result to be unspecified, and we should consider allowing this exception.
This proposal is only to allow an explicit exception to make NaN comparisons unspecified, regardless of the semantics. Vote no-exception (or anything other than unspecified) to require NaN comparisons to follow directly from #460.
The default of unspecified still holds from the previous invalidated ballot.
Rationale: There is not enough agreement about this to make a requirement. NaN's can be addressed specially by code that uses them.
Procedures are another case for contention with eqv?. In R3RS, an operational equivalence was defined for procedures, and this was subsequently removed.
R6RS went the other direction and allowed the exact same procedure x to return #f for (eqv? x x), and R7RS currently reaffirms this. The rationale behind this is for compiler optimizations such as inlining local procedures, that is given:
(let ((square (lambda (x) (* x x)))) (eqv? square square))it is reasonable for a compiler to perform the optimization:
(eqv? (lambda (x) (* x x)) (lambda (x) (* x x)))in which case the result would naturally return #f.
Vote yes to allow the result to be #f.
The default of yes still holds from the previous invalidated ballot.
Rationale: Absolutely not. This would mean that even eq? wouldn't work after such an optimization.
Currently, R7RS-small says that when equal? is applied to records that are not eqv? (that were constructed by different calls to the record constructor), the result may be #t or #f at the implementation's discretion. The proposal is to treat records of the same type like pairs, strings, vectors, and bytevectors: that is, their contents are recursively compared.
Vote recursive to require recursive comparison of the record's fields, identity to return #t iff eqv? does, and unspecified to leave this open.
Note equal? is already required to handle cycles regardless.
Rationale: This is merely making equal? on records consistent with equal? on other data types.
Specifically, does it indicate case-folding and normalization support for the repertoire of any particular version of Unicode, or any version greater than 5 or 6 or 6.1, or no particular version?
Full unicode refers to the set of characters available. Case-folding and character predicates are required to work according to the Unicode standard for all supported characters. The question of which version of Unicode the property refers to is important. We could require a specific version (and all further revisions), or always require the latest official Unicode standard, in which case an implementation would not be compliant until it was updated with each new standard. Alternatively, we could parameterize the feature identifier, so that implementations might claim to support (full-unicode 6), (full-unicode 6.1), etc.
Rationale: Specifying latest is unrealistic. That would mean that existing Scheme implementations would fall out of compliance the moment a new Unicode standard was promulgated. Specifying a point version, e.g. 6.1, is also unrealistic, as the version of Unicode that a particular implementation is reasonably able to support depends so much on underlying facilities provided, for example, by the operating system.
There have been a bunch of complaints about the formal semantics: it's incomplete, it cannot be mechanized with a proof assistant, it doesn't help either users or implementers very much, and so on. See in particular #453.
The semantics have been updated to include dynamic-wind, however the other arguments still hold.
This proposal is to remove it from the report altogether, and to urge the Steering Committee to create a new WG to produce one, likely in a "rolling" style with increasingly comprehensive releases, on its own schedule. Some members of the current WG have expressed interest in serving on such a group, and others have expressed their complete lack of interest, so a new WG seems the best choice if this is done.
Alternately, we can adapt the operational semantics from R6RS.
Rationale: I've never understood the fascination with formal semantics, particularly considering that they're non-normative,
English right, then adjust the formal semantics to match. In all my years of using the RnRS specifications for reference, I have not once referred to the formal semantics in order to understand some point of the language.
Nevertheless, the formal semantics do matter a lot to many people in the community. Removing them, even temporarily, will probably cause us to lose support for the draft. I'm afraid that we're going to have to find a way -- some volunteers? -- to bring that part of the document up to date.
There's no point in adopting the operational semantics from R6RS since it's not compatible with R7RS.
R5RS says it's an error for a key to appear in more than one clause of case (or twice in the same clause, but that's trivial). R6RS allows the same key to appear more than one clause, but insists on left-to-right testing throughout, like cond. The R6RS editors thought this was better for machine-generated code, though worse for hand-written code.
The proposal is a compromise: allow keys to appear in more than one clause, but behave as if the key appeared only in the first (leftmost) clause. This allows hash-table or other non-left-to-right implementations.
Rationale: The argument from machine-generated code, e.g. macros, makes perfect sense, but the leftmost proposal gives implementations more freedom to achieve the same ends.
Following exactly in the footsteps of R6RS we voted for a blob API and then changed the name to bytevector.
Formal comment #435 argues that u8vector is in more common use, so this item is being re-opened. The default is the current draft bytevector, and for any member leaving the preferences are left blank their votes from ballot 3 will be used.
Rationale: While "blob" is a widely used term these days, I prefer a properly hyphenated, descriptive term, or at least a descriptive term. I've never liked "blob," even knowing that it abbreviates "Binary Large OBject." Since R7RS is case sensitive, we don't need even more cases where the capitalization of an abbreviation is not matched in the names of Scheme identifiers. Furthermore, it has been ages since "byte" meant anything other than eight bits, so there's no need to choose "u8" or "octet."
While Marc's argument that we (and implementers of the widely adopted SRFI 4) use "#u8(" to prefix literal byte vectors is compelling, the idea of byte vectors is to provide the basis for a more complete system in WG2 Scheme that supports reading and writing not only unsigned bytes, but also other data types, e.g. IEEE floats, and mixed types as well. It's useful to distinguish this idea by name even if the underlying data type is the same.
For ease of implementation, the proposal is to make it an error for an imported identifier to be referenced or defined in a library before the library declaration that imports it. This allows strict left-to-right processing of library declarations, with no need to delay processing till the end of the library.
Therefore, this would be an error (but still permitted as an extension in Schemes that can easily provide it):
(module (begin (define x y)) (import (library defining y))This would necessitate replacing the penultimate paragraph of section
One possible implementation of libraries is as follows: After all cond-expand library declarations are expanded, a new environment is constructed for the library consisting of all imported bindings. The expressions and declarations from all begin, include, and include-ci declarations are expanded in that environment in the order in which they occur in the library declaration. Alternatively, cond-expand and import declarations may be processed in left to right order interspersed with the processing of expressions and declarations, with the environment growing as imported bindings are added to it by each import declaration.
Vote yes to add the restriction, or no to leave it out.
Rationale: I'm not sure why we even allow begin, include, or include-ci before any import or export form. The proposed restriction is not limiting, and simplifies not only implementing the library system, but also reading code that uses it.
This is a proposal to limit numbers in library names to the range 0 to
can assume as the maximum size of an integer.
Numbers are mostly used for SRFI-based libraries anyway, which are not likely to reach either limit.
The option uint15 for the proposal as stated (0 to 32767), int16 for -32768 to 32767, int24 for -223 to 223-1, etc.
Vote unspecified to make no explicit requirement on the integers allowed in library names.
Rationale (from my earlier ballot on #349): Twenty-four is too many bits to require for tiny implementations. I'm nervous about burdening the smallest implementations with even a sixteen-bit requirement, but such implementations typically already leave out significant language features, so I'm willing to ask for 16 bits.
Add the following text to the discussion of library loading:
Regardless of the number of times that a library is loaded, each program or library that imports bindings from a library will receive bindings from a single loading of that library, regardless of the number of import or cond-expand declarations in which it appears.
to make it clear that, for example,
(import (prefix (foo) 'foo:)) (import (only (foo) bar))will cause bar and foo:bar to come from the same instantiation of the library '(foo)'
Vote yes to add this requirement.
Rationale: Yes, we don't want people to interpret import as a statement causing an import to happen rather than a declaration that one should. However, the wording still isn't clear, and in fact seems to suggest the opposite of its intent. I recommend this instead:
Regardless of the number of times that a library is loaded, all the bindings it exports to any loading program or library will come from a single loading of that library, regardless of the number of import or cond-expand declarations in which it appears.
Add an export-all form to the library declaration that means "export all identifiers that are defined in the library with begin, include, and include-ci but none that are imported with import."
Rationale: This will be a common usage pattern. It's much better than the alternative suggestion, which was to make all identifiers be exported if none are. That violates the principle of least astonishment.
I don't understand Alex's argument that this will be hard to implement. If something like that is hard, we're doing something wrong.
The proposed include-library-declarations allows a library to incorporate a file containing arbitrary library declarations, not just Scheme code (definitions and expressions). This allows, for example, the exports of a module to be written directly in the library file, and its imports in a separate file.
An alternative would be something like (export-from <library>) to export the same bindings as another library. This does require the clumsiness of actually defining the identifiers in the other library if it is abstract.
Rationale: I don't understand why writing the imports in a separate file is a good idea. I view the imports and exports as part of a "wiring diagram" showing how parts of the system are connected, not a way of declaring an abstract interface. In any case, this is invention, not something that exists in Scheme implementations already, so it doesn't belong in the standard.
R7RS currently says:
Within a program, each imported library is loaded at least once, and, if imported by more than one program or library, may possibly be loaded additional times.
Richard Kelsey thinks this is too liberal, and proposes:
Regardless of the number of times that a library is loaded, each program or library that imports bindings from a library will receive bindings from a single loading of that library, regardless of the number of import or cond-expand forms in which it appears.
Aaron Hsu, however, thinks this is too restrictive, and proposes (backed up by actual R6RS implementations):
If a library's definitions are referenced in the expanded form of a program or library body, then that library must be loaded before the expanded program or library body is evaluated. This rule applies transitively.
Similarly, during the expansion of a library, if a syntax keyword imported from a library is needed to expand the library, then the imported library must be visited before the expansion of the importing library.
Rationale: Our library system is designed to have simple semantics, and divergence from once-and-only-once makes it harder to reason about. If we are going to do something else, let's still make sure that modules aren't loaded more than once.
Coverage for this R6RS feature is currently sparse: only Gauche, Chez, Vicare, Larceny, Ypsilon, Mosh, IronScheme, KSi, RScheme, Rep support it. But it is convenient when working in bases other than e such as 10, 2, or 16, and it is just a few extra lines of code, since `(log z b) => (/ (log z) (log b))` for arbitrary complex numbers z, b.
Vote yes to add the optional second argument from R6RS.
Rationale: This is simple, widely useful, and conforms to R6RS.
Draft 6 says that it's an error for an argument of / (other than the first) to be an exact zero. R6RS, however, says that it's an error only if all the arguments are exact. In other words, (/ 2.0 0) is an error according to the draft, but in R6RS it returns +inf.0 (assuming the implementation supports it). The proposal is to adopt the R6RS wording.
Cowan tested (/ 2.0 0) in the usual set of Schemes:
Vote error for the current draft semantics that it is an error, all-error for the R6RS semantics that it is only an error if all arguments are exact, or unspecified to make this case unspecified.
Rationale: Division by zero is still typically a mistake, and catching it as early as possible is a good idea. Until we specify how an implementation goes into IEEE non-signalling mode, we should continue signalling such errors.
R5RS requires that - and / accept one or two arguments, and labels support for more than two as "optional". R6RS requires such support. The proposal is to require it.
All Schemes in the test suite support more than two arguments except Scheme48/scsh. (Owl Lisp does not support variadic procedures of any kind.)
Vote require for required n-ary behavior and optional to leave it optional as in R5RS. Alternately, vote forbidden to make this always an error in all implementations.
Rationale: It's not hard to make this just work, and almost all Schemes already support it.
R5RS and draft 6 of R7RS don't say what (log 0.0) and (log 0) return. R6RS requires -inf.0 and an exception respectively. The proposal is to say that (log 0.0) returns -inf.0 on systems that have -inf.0, and that (log 0) is an error.
In Racket, Gambit, Chicken (with the numbers egg), Guile, Chibi, Chez, Ikarus/Vicare, Larceny, Ypsilon, Mosh, IronScheme, STklos, Spark, (log 0.0) returns -inf.0 and (log 0) raises an exception.
Gauche, MIT, Chicken (without the numbers egg), Bigloo, Scheme48/scsh, Kawa, SISC, SCM, NexJ, KSi, RScheme, XLisp, Rep, VX, SXM, Inlab return -inf.0 in both cases.
Elk, UMB, Oaklisp raise an exception in both cases.
Scheme 7 returns the wrong answer in both cases.
SigScheme, Shoe, TinyScheme, Dream, BDC, Owl Lisp don't support log.
Scheme 9 apparently goes into an infinite loop in both cases.
Vote r6rs for the R6RS behavior of returning -inf.0 and raising an error, respectively. Vote infinity to always return -inf.0.
Rationale: Let's catch errors early.
This proposal allows (/ 0 x), where x is an inexact number, to return an exact value. Currently only Racket, Gambit, TinyScheme, Sizzle, Spark do this; see Zero for details.
Vote zero to allow (but not require) this to return exact 0. Vote no-nan to allow it to return 0 except when x is +nan.0, where it would return +nan.0.
Rationale: Zero divided by anything is zero. We know the answer exactly given only an exact numerator, so we should return an exact answer. However, as John points out, a NaN may indicate an earlier error, and we shouldn't require masking that.
Currently R7RS says nothing about the value of (max +inf.0 +nan.0) or (min -inf.0 +nan.0). R6RS required these functions to return the infinite value, but this was adopted by some but not all R6RS implementations (see MaxInfNan for details). R5RS implementations are also divided.
The proposal is to allow R7RS implementations to provide either value.
Vote both to explicitly add a note that either are allowed, infinity to require the infinite value as in R6RS, nan to require returning +nan.0, and unspecified leave unspecified (i.e. the same as both but without the note).
Rationale: I'm changing this for the same reason I changed my answer to #407, i.e. because a NAN may indicate an earlier error and we shouldn't lose the information that there was an error.
Currently both infinite? and nan? return #t to a complex number like +inf.0+nan.0i. Is this the Right Thing, or should infinite? only return #t if neither part is a NaN?
Note it is reasonable for an implementation to not support partial nan complex numbers.
Vote disjoint to ensure that infinite? and nan? are disjoint predicates as in the proposal, or overlap to allow the current behavior.
Rationale: I'm not sure how useful it is to ask whether a complex number is infinite, but the only reasonable interpretation I can see is that if either part is infinite, the complex number is. If we don't agree on that, I can't see any value in leaving this unspecified, so let's make them disjoint.
Currently R7RS is silent on what truncate, floor, ceiling, and round do when the argument is +inf.0, -inf.0, or +nan.0. R6RS has them return the argument, which seems reasonable.
Tests were made for (round (* 1.0e200 1.0e200)) on a variety of implementations.
Racket, Gauche, Chicken (with and without the numbers egg), Bigloo, Guile, Kawa, Chibi, Chez, SCM, Ikarus/Vicare?, Larceny, Ypsilon, Mosh, IronScheme, NexJ, STklos, KSi, Shoe, BDC, Rep, Schemik, Elk, Spark all return the argument.
MIT, Gambit, Scheme48/scsh, SISC, Scheme 9, Scheme 7, signal errors.
SigScheme, TinyScheme, Dream, UMB don't work for one or another reason.
Oaklisp and Owl Lisp don't do flonums.
XLisp only has fixnums and flonums, and returns the largest or smallest fixnum as the case may be.
RScheme returns a variety of slightly strange values: (round +inf.0), for example, is 0, but (round -inf.0) is -inf.0.
Vote input to return the input, error to specify "it is an error", and unspecified to leave unspecified as in the current draft.
Rationale: Let's catch errors early. The whole point of these procedures is to return integers, so returning something that is not an integer makes no sense. If we don't do that, we should leave the result unspecified rather than force implementations to do the wrong thing even if it is compatible with R6RS.
There are two useful subsets of the exact numbers, both of which are commonly called natural numbers, depending on who's talking. Logicians, set theorists, and computer scientists include 0, other mathematicians mostly don't. This proposal adds the predicates exact-positive-integer? and exact-non-negative-integer?, analogous to exact-integer?. Because of the ambiguity, the name natural-number? is not proposed.
Vote yes to add these two procedures.
Rationale: We don't need more names in WG1.
Whitespace characters include the space and newline characters. (Implementations may provide additional whitespace characters such as tab or page break.)
However, 7.1.1 has:
<intraline whitespace> -> <space or tab> <whitespace> -> <intraline whitespace> | <newline> | <return>
So 2.2 implies that supporting tabs is allowed but not required, yet
Vote required to require support for tab as a whitespace character by read. char-whitespace? is required to return #t for it regardless.
Rationale: How can this be in question? It's just basic ASCII, as is page break, for that matter.
Currently we don't specify what display does with circular lists. Should it generate labels like write, or loop like write-simple, or leave it unspecified?
Rationale: Why are we requiring that basic I/O operations be expensive? I shouldn't have to allocate memory just to print a list.
The #!fold-case and #!no-fold-case directives are read as comments, which means that they are treated as whitespace (section
implicit. This means that (1#!no-fold-cases) reads as (1 s). This seems unfortunate.
Rationale: Requiring a delimiter (presumably including end of file) is simple and consistent. Even if we don't do that, we shouldn't stick with the status quo, which is bizarre.
There is concern that the output of write cannot be read by non-R7RS implementations. This is not a strict requirement, but is reasonable if using simple sexp-based file/interchange formats.
Specifically, even though there are no cycles in
(let ((x (list 2))) (write (list x x)))
it previously output "((2) (2))" but now outputs "(#0=(2) #0#)".
The WG concern is that R5RS write is unsafe, easily causing infinite loops, and should therefore not be the default. Thus we renamed this "write-simple", requiring programmers to know they are writing a "simple" data structure up front.
Arguably, there are three procedures desired:
although even for write-shared people sometimes want to treat containers such as strings separately.
Note the algorithms for detecting shared structure differ from those for detecting cycles, so providing both -shared and -cyclic imposes an additional implementation burden.
Rationale: We shouldn't make such a basic, incompatible change in a core language feature (i.e. write) even in the interests of preventing infinite loops. Furthermore, write shouldn't have to allocate memory just to print something, particularly considering that the vast majority of uses will have no cycles.
Scheme used to use #!true and #!false before abbreviating to the #t and #f syntax.
In draft 4 we added these back in as aliases, without the "!" now that tokens are required to be delimited so there would be no ambiguity.
Some objections were made to the new syntax which generated a lot of discussion, so we are re-opening this ticket. The default is the previous decision to add #true and #false as aliases.
The primary objection is that boolean literals are very common, and this introduces needless incompatibilities with non-R7RS systems, and potential confusion in documentation.
The counter-argument is that these are more readable and friendly to beginners, and allow easy visual distinction in long lists of booleans. We retain full backwards compatibility and are under no obligation for non-R7RS systems to be able to run R7RS code.
Note that Racket and Chibi independently adopted this same syntax unaware of each other. Chicken also supports this via its SRFI-38 implementation.
Rationale: The long form is more readable, I suppose. However, I'm worried that non-R7RS implementations will no longer be able to read values of this most basic type.
Currently, we allow implementations to provide their own names for characters, but provide no guidance for them. There are two plausible sources: the names in the Unicode Standard, and the [http://www.w3.org/TR/xml-entity-names/ entity names specified by W3C] for use in HTML, MathML, and other markup standards (ultimately derived from ISO SGML character entity sets).
The Unicode names are in all upper case and contain significant spaces and apostrophes as name characters, which would require some mapping to make valid Scheme identifiers. The W3C name list is incomplete though fairly large (currently 2237 names), covering mainly the Greek and Cyrillic scripts and non-ASCII punctuation and symbols. It distinguishes between iota (small) and Iota (capital).
Vote w3c for the W3C list, unicode to use the Unicode list with names mapped by converting to lowercase and replacing any non-identifier character (space and apostrophe) with hyphens. Vote unspecified to leave the character name extensions entirely up to the implementation.
Rationale: There isn't agreement among implementations on this. If we do specify it, we should specify Unicode to be consistent with all our other support for Unicode, which is the most carefully thought out standard in any case.
With the acceptance of #278, we reduced the set of division operators to truncate-* and floor-* and move these into the base library. Three of these procedures are simply aliases for quotient, remainder and modulo, so it is worth considering removing the old names.
Since the old names are in IEEE Scheme we need strong justification for removing them from (scheme base), and even if we do so they will remain available in (scheme r5rs).
We have precedence for changing names, but only in the case when the existing names were both actively misleading and had already been changed in R6RS. Specifically, in ticket #328 we replaced the names inexact->exact and exact->inexact with the more accurate exact and inexact.
Arguably the new division operator names are clearer, but the old names are not actually misleading.
Vote yes to remove the old names from (scheme base), or no to leave them in as aliases.
Rationale: I don't have a strong preference, so I'll go with not breaking existing code.
This is compatible with Chicken, and "more Scheme-like, less Java-like". Okay, it's bikeshedding.
Rationale: Yes, the "get-" prefix adds nothing here.
We should consider removing it from get-output-string, get-output-bytevector, get-environment-variable, and get-environment-variables as well.
Under this proposal, the name would be bytevector-copy and the signature would be
(bytevector-copy bytevector [start [end]])
Vote yes for this simplification.
Rationale: The naming convention "-partial" is neither widely used nor consistent with naming elsewhere in the draft.
One proposal is port-last with a signature of:
(write-bytevector ''bytevector'' [''start'' [''end'' [''port'']]])
This has the disadvantage of being required to call bytevector-length when writing to a specific port.
Alternately we could do offsets-last:
(write-bytevector ''bytevector'' [''port'' [''start'' [''end'']]])
which has the disadvantage of separating the bytevector from its offsets.
Alternately, vote separate to keep these as two separate procedures.
Rationale: Alex says that we should optimize for the most common use case, and I agree, but I believe that that's writing a range of the byte vector, not writing to a different port. After all, as John points out, the latter can be accomplished using a parameter.
This is a proposal to add optional start (inclusive) and end (exclusive) arguments to string->vector and vector->string. We now have start (inclusive) and end (exclusive) arguments for string->list and vector->list, but our non-R5RS and non-SRFI procedures to convert directly between strings and vectors don't provide these.
Vote yes to add these optional arguments.
Rationale: Yes, these are useful, and we should be consistent. Alex says that using indexes with strings is a mistake, but I disagree. Arbitrarily indexing into a string and expecting to find a well-formed substring may be a mistake, but it should still be possible to remember safe offsets while creating a string and use them later.
R7RS requires an error to be signalled (which means an exception is raised as if by raise) in the following circumstances:
This proposal is to provide four standard predicates that identify these specific conditions, to be used in guard clauses or in with-exception handlers as a portable means of detecting these errors. Although these predicates may return #t on other objects, if one reports #t on an object, the others must report #f. Proposed names are file-error?, scheme-report-error?, read-error?, and expt-error? respectively.
Vote yes to add these procedures, or file-only to only add the file-error? predicate, and file+read to add the file-error? and read-error? predicates.
Rationale: I'm disappointed that we have an exception system without a standard taxonomy even in WG1, so this will provide at least some relief. Alex argues that all of these situations can be checked for in advance, but that's not true. For example, checking that a file exists and is accessible before opening it opens one up to a race condition. Also, the only way to determine whether EOF will be found in the middle of reading a datum is to implement a separate parser, at which point read becomes useless.
We should define the predicate record? so that it's possible to distinguish instances of record types from all other types. It should not be necessary to enumerate all record type predicates in order to determine whether an object is an instance of a record.
This is Alexey Radul's suggestion.
Rationale: Why shouldn't one be able to distinguish instances of record types from instances of other types? John says that having record? would prevent WG2 Scheme from supporting opaque records because it would be possible to recognize them as instances of record types. So what? What's the harm in being able to recognize them as such? Could a programmer do anything malicious with that information?
This was requested by Formal Comment #424.
These procedures would be provided for parallelism with the byte-vector I/O operations:
|
Byte |
Character |
Bytevector |
String |
|
read-u8 |
read-char |
read-bytevector(!) |
read-string(!) |
|
write-u8 |
write-char |
write-bytevector |
write-string |
If #385 passes, optional start (inclusive) and end (exclusive) index arguments would be added to write-string. Otherwise write-partial-string would be provided.
Vote yes to add all three, immutable to add only read-string and write-string, or no to leave them out.
Rationale: I'm alarmed that we made it this far without write-string.
Marc Feeley proposes it should be possible to convert from any container type to another, possibly via an intermediary such as
(list->B (A->list a))
proposing specifically "list" be the universally available intermediary, although "vector" would also be worth considering.
The container types are list, vector, string and bytevector. String and bytevector are second-class in that they are not general-purpose container types, and may raise errors converting from lists or vectors.
Vote list for the proposal to add the following procedures to complete the cycle:
Vote vector to add the equivalent procedures to allow converting between any of the types and vectors, specifically the following two new procedures:
Vote list+vector to add both list and vector conversions.
The latin-1 proposal also adds the Latin-1-centric ideas of string to bytevector conversion, where each element of the bytevector is converted to/from a character with char->integer/integer->char.
The matrix proposal requires all 43=64 conversions.
Rationale: I don't see the point. These conversions are generally wasteful, especially as simple intermediate values, and direct conversions would be better. However, we shouldn't include the full direct conversions matrix because that's just too large, especially for WG1.
This is for completeness with append and string-append. See #436 for the Formal Comment that triggered this ticket.
Rationale: Yes, for consistency and completeness.
This is for consistency with append, string-append, and vector-append (per ticket #444) procedures.
Rationale: Yes, for consistency and completeness.
Replace port-open? with input-port-open? and output-port-open?, since a bidirectional port can be closed on one side without the other. See Formal Comment #439.
Vote replace to replace port-open? with just the two new versions, or add to have all three.
Rationale: Otherwise it's unclear what port-open? means on a bidirectional port.
Marc Feeley writes:
It is a bad idea for the fill parameter of vector-copy to have a default. When fill is absent, it should be an error when start and end are not within the bounds of the sequence. Otherwise, some index calculation errors (off-by-one on end) may go unnoticed. Moreover, when it is supplied, fill should also be used when start is less than 0, for consistency with the case where end is greater to the length of the sequence.
Vote required to make the fill parameter required, error to make it an error in the case that fill is absent yet needed, remove to remove the fill parameter and signal a runtime error if end is longer than the input vector, or default for the current status quo.
Rationale: While allowing the fill parameter to have a default value is compatible with SRFI 43, Marc's argument about detecting errors is strong. However, I disagree that the idea of allowing start to be negative is somehow more consistent. The obvious application of the fill parameter is implementing variable-length data structures out of vectors, extending the original in the process. However, using the name vector-copy for this purpose is an awkward overloading. A separate procedure, not defined in WG1 Scheme, should be used for that purpose.
I've updated WG1Ballot, so others should adjust their votes if they see fit.
Pass exception handlers a second, Boolean argument that declares whether the exception is continuable.
Rationale: I would like to see this, too, but agree that passing it to every handler is overly verbose considering how rarely it would be used. We should address this in WG2 where we will, I hope, have a more powerful exception system.
Per ticket 464, add optional start and end arguments to utf8->string and string->utf8.
Vote both to add optional start and end arguments to both, string->utf8 or utf8->string to add them to only one procedure, or neither to leave both unchanged.
Rationale: As Marijn says, it's useful to be able to avoid extra copying while decoding a string. We should change both for symmetry.
See Formal Comment #372 for the argument. Cowan writes: "I support this proposal. I don't support the alternative proposal to just say that any true value reports success and only #f reports failure, for there is usually only one kind of success (0 on Posix and Windows, "" on Plan 9, 2 on VMS) and many kinds of failure."
It is reasonable and convenient to use #t/#f as generic success/failure for portable programs, with (exit) as a shorthand for the "normal" completion (exit #t).
Another reasonable extension is fallback for certain success values that the implementation cannot understand. Specifically, 0 is commonly used for success on Posix systems, and the empty string "" as success on Plan9. We could require that if the implementation does not know how to pass these value types (string or number) to the OS, then it should recognize 0 and "" as true. Any value other than these which cannot be passed to the OS should be treated as a generic error. That way, a program written for Posix that alternatively uses (exit 0) and (exit <n>) will still work as desired on a Plan9 system, only losing details of the type of failure (and likewise for Plan9 programs running on Posix).
In either case, unless someone makes a proposal to the contrary, unknown values should always be treated as generic failure, and never raise an exception or fail to exit (from #374).
Rationale: Making (exit #t) have the same effect as (exit) is a no-brainer. I can see no portable reason to treat the empty string and zero specially.
This procedure provides instant guaranteed process exit without running dynamic-wind thunks. This is a low-level and dangerous procedure.
Vote emergency-exit to add this procedure, or no to leave it out. If you want to write in an alternate name, be sure to include emergency-exit as a secondary option after it.
Rationale: I hate the name, but it makes sense to be able to exit immediately. Frankly, I'd rather that exit did this, or that its behavior with regard to dynamic-wind was unspecified. It's my impression that people use exit when they want their program to stop immediately. They don't want a dynamic-wind form to prevent their exit, for example.
I suggest the name exit-immediately.
Cowan writes:
"I have reluctantly come to the same conclusion as the R6RS editors: that in a Scheme with libraries, scheme-report-environment and null-environment don't make much sense. They are not in IEEE Scheme or R4RS, so there is no formal barrier to removing them.
"Semantically, scheme-report-environment holds all the identifiers in R5RS, excepting any which the implementation doesn't provide, like make-rectangular if it does not have complex numbers. Null-environment, on the other hand, contains only the syntax keywords with none of the standard procedures: it is not an empty environment. R6RS preserves these procedures only in the R5RS compatibility library, where they expose only R5RS content.
"When adapting the definition to R7RS, I changed scheme-report-environment to contain all the identifiers in all the standard libraries that the implementation provides, and null-environment all the syntax keywords in those libraries. This was the best I thought I could do, but now I think that it provides very little utility.
"It's possible to construct any specific environment you want by using the environment procedure, which turns a sequence of import-specs into an environment. In particular, we now have the (scheme r5rs) library, which essentially provides what (scheme-environment-procedure 5) should provide, and there is no portable use of any argument other than 5."
Vote remove to remove these two procedures entirely, or move to move them from (scheme eval) and provide them only as portability options in (scheme r5rs), where only the argument 5 is required to be supported. Vote keep to leave them as-is.
Rationale: I see John's point, but we shouldn't break compatibility with R5RS.
The proposal is to require eval to accept definitions as well as expressions, as long as the specified environment is mutable. See EvalDefine for which Schemes already handle this.
Rationale: eval should accept the full language, including defines.
The standard allows the following extension to force:
Some implementations may implement "implicit forcing," where the value of a promise is forced by primitive procedures like `cdr' and `+'
We should remove this note or tighten the definition.
A simple definition is any primitive that would require a type-check can perform implicit forcing. This would include all type predicates themselves except for promise?. Note if #405 passes, then in implementations which support this extension an object could return #t for promise? in addition to one other type.
I don't see any reason to change this.
Currently there is no way to inspect an object to see if it's a promise. This proposal makes promises first-class by adding a promise? predicate. It also requires that if the argument to make-promise is a promise, it is returned without rewrapping it, and that if force is given a non-promise argument, it returns it unchanged. (These things cannot be provided by the user without a promise? predicate, and are trivial to provide with it.)
Vote disjoint to add promise? and make it a disjoint type, or yes to add it as a not-necessarily disjoint predicate.
Rationale: The promise? procedure is useful, as the examples above demonstrate. Once we support promise?, keeping them disjoint seems easy, since if one implements them directly as procedures, one can't provide promise? without an inefficient table lookup anyway.
The definition of read-line allows implementation defined extensions to the set of end of line sequences. This is arguably too loose, as an implementation could define "a" as and end of line. On the other hand, if we do want to leave this in it may make sense to remove "\r", which is no longer used in any contemporary OS.
Vote no-extensions to forbid implementation defined extensions, no-return to remove a single return from the list of required end of lines, and none to leave as-is.
Rationale: Implementations are going to define extensions, and it's unreasonable to expect them not to.
In ballot 4, in symmetry with the new Unicode definition of char-numeric? and as an analog to CL's digit-char-p, we provided digit-value.
An informal comment was made questioning this procedure, and suggesting if provided at all it be extended to hex digits.
Vote ascii-hex to support only the ASCII hex digits a-f,A-F (in addition to full Unicode numeric digits), unicode-hex to support all Unicode variants of a-f,A-F (need to define formally).
Vote ascii-radix or unicode-radix to have both digit-value and char-numeric? take a radix argument, such that char-numeric? returns #t and digit-value returns the appropriate value for characters representing non-numeric digits of that radix under ASCII or Unicode character encodings, respectively, and for characters representing numeric digits under Unicode. Implementations are required to support at least the radix values: 2, 8, 10, and 16, and may support others.
Vote remove to remove digit-value entirely, remove-radix to remove digit-value entirely, but add the radix argument to char-numeric? as described above, or keep to keep as is.
Rationale: We've strayed into invention territory here, providing something that existing implementations don't. If we do keep it, it should support ASCII hex for compatibility with string->number.
Our charter calls for one or more reference implementations. As of today, Chibi is very close to being so. The proposal is to bless it as a sample or model implementation, but not technically a reference implementation -- if it disagrees with the standard, the standard wins.
Rationale: Chibi is the one implementation that be considered a reference implementation, and we are supposed to provide one, so let's make it official. Thank you very much to Alex for doing the work to make this happen.
We currently use the singular form of data types for library names,
in (scheme lists) and (scheme records). We should decide officially which is preferred.
Rationale: I'll bikeshed for the singular. (I'm assuming that what we're saying here is that we'll change all of the data type names we use, not that we're saying anything about the names people use for purposes other than standard data types.)
If the value of current-jiffy is to be both space-efficient (that is, a fixnum) and reasonably precise (say, microsecond timing), it needs to wrap around: 30-bit fixnums on a 32-bit system will wrap every 17 minutes. That means an application needs to know what the maximum value is before it wraps back to zero. The jiffy-modulus function returns the maximum value of the current jiffy plus 1. Alternatively, jiffies can be signed and wrap from (- (jiffy-modulus) 1) to (- (jiffy-modulus)), which is easier for the implementation but harder for the user.
Rationale: I don't know what existing implementations do.
In ticket #11 we voted to make the reader case-sensitive by default. In ticket #92 we further added the R6RS #!fold-case and #!no-fold-case reader extensions. In both cases the terminology was lax and simply referred to "reader case sensitivity", and all discussion centered around symbols, although in R6RS character names were also affected.
Case folding will apply to numeric literals, booleans and bytevectors regardless, as they do in both R5RS and R6RS. We need to clarify how character names and the case folding directives themselves are handled.
The default is r6rs, where character names are case sensitive by default and folded by the #!fold-case flag:
http://www.r6rs.org/final/html/r6rs-app/r6rs-app-Z-H-4.html#node_chap_B
Alternately character names could be made to ignore the reader directives and always or never fold case. Never folding case breaks R5RS and earlier compatibility without any easy workaround.
These same settings apply to the include-ci syntax.
Rationale: I see no reason to differ from R6RS here.
This proposal stems from remarks by Alaric Snell-Pym and Will Clinger on the r6rs public mailing list. If eq? is allowed to return #f on two procedures when eqv? nevertheless returns #t, as is already the case for numbers and characters, then more intelligent implementation-specific procedure comparisons using eqv? are possible, while still keeping eq? simple enough to inline easily.
Note that this is orthogonal to the question of #460, how eqv? works on procedures. There should be little or no backward-compatibility hit for this change.
Rationale: I will defer to Will's long experience in compiler implementation.