We decided on module earlier, and the current draft reflects that, but some comments from the community suggest we revisit this issue.
Emails from Aaron Hsu and Denis Washington:
[AH] I do not buy the argument that we are making things better by using `module` instead of `library` in this case. The module term is much more common throughout, including systems in Chez, PLT, Scheme48 (I believe), among others. [...] [DW] (Bigloo and Chicken are two others which use `module` for existing forms.) I feel that clashing with all of these implementations substantially increases the burden for these systems' implementors to adopt to R7RS. [...] [DW] What about `define-library`? It might be slightly confusing as it sounds a bit procedural for a purely syntactic construct, but it does not seem to clash with any existing implementation (as far as a quick Google search reveals, at least [as well as direct testing --JC]) and preserves the "library" term, which is common, well-known, clear and in line with previous Scheme specs (R6RS and, in a way, R5RS' usage of the term "library procedure").If we choose a unique name such as define-library then there is no chance of conflicts, but the name itself may not be aesthetically pleasing.
If we choose an existing name, implementations may have difficulty distinguishing between their native form and the R7RS module syntax, possibly requiring a command-line flag for "R7RS mode" or some such.
TODO: Create a list of existing names used, and ways implementations may detect the difference in the event of a conflict.
If the name isn't already being used _anywhere_, it means it's a bad name.
R6RS introduces a description of requirement levels following RFC 2119 use of the modal verbs "may", "should", "must", "shall", "should not", "must not", "shall not."
Do we want to incorporate this? If so, we'll also need to revise existing uses of those phrases, and possibly introduce them where needed.
We are re-opening the sixth "centered" division operator:
These correspond to the R6RS operators div0, mod0 and div0-and-mod0 defined as in the Guile manual:
These procedures accept two real numbers x and y, where the divisor y must be non-zero. centered-quotient returns the integer q and centered-remainder returns the real number r such that x = q*y + r and -|y/2| <= r < |y/2|. centered/ returns both q and r, and is more efficient than computing each separately. Note that centered-quotient returns x/y rounded to the nearest integer. When x/y lies exactly half-way between two integers, the tie is broken according to the sign of y. If y > 0, ties are rounded toward positive infinity, otherwise they are rounded toward negative infinity. This is a consequence of the requirement that -|y/2| <= r < |y/2|.Vote centered to add the sixth operator, no to stick with the five operators, and remove to drop the full five sets of operators from the small language.
We need to use and understand all of these operators more before deciding. Some of the newly proposed operators have no known use in existing programs to my knowledge.
A suggestion was made to specify that arguments in a procedure call and "init bindings" (presumably in let and friends) should evaluate to exactly one value. Currently it is "an error" to pass a non-single value to any continuation not created with call-with-values, which means implementations are free to add their own handling of this (e.g. raising an error or taking just the first value as in CL).
Do we want to require implementations to signal an error in these cases? Not currently many implementations of MV would not be able to detect these cases efficiently.
No, this is silly.
These date back to R4RS, when Scheme had a fixed syntax and it made sense to enumerate it here. Are they still doing useful work, now that syntax forms can be changed at will?
Vote yes to remove them.
Drop these, they don't belong when describing a language without fixed syntax.
Change load to take a second argument which is the environment to load into. The default is (interaction-environment).
See also #161.
This accepts a character which is a numeric digit and returns its value as a digit, or #f if it's not a digit:
(digit-value #\3) => 3 (digit-value #\x0664) => 4 (digit-value #\x0EA6) => 0You need the following list of zero-value characters to implement this for all of Unicode (currently); implementations that support only a subset of Unicode need only a subset of the list, of course:
(define zeros '( #\x0030 ;DIGIT ZERO #\x0660 ;ARABIC-INDIC DIGIT ZERO #\x06F0 ;EXTENDED ARABIC-INDIC DIGIT ZERO #\x07C0 ;NKO DIGIT ZERO #\x0966 ;DEVANAGARI DIGIT ZERO #\x09E6 ;BENGALI DIGIT ZERO #\x0A66 ;GURMUKHI DIGIT ZERO #\x0AE6 ;GUJARATI DIGIT ZERO #\x0B66 ;ORIYA DIGIT ZERO #\x0BE6 ;TAMIL DIGIT ZERO #\x0C66 ;TELUGU DIGIT ZERO #\x0CE6 ;KANNADA DIGIT ZERO #\x0D66 ;MALAYALAM DIGIT ZERO #\x0E50 ;THAI DIGIT ZERO #\x0ED0 ;LAO DIGIT ZERO #\x0F20 ;TIBETAN DIGIT ZERO #\x1040 ;MYANMAR DIGIT ZERO #\x1090 ;MYANMAR SHAN DIGIT ZERO #\x17E0 ;KHMER DIGIT ZERO #\x1810 ;MONGOLIAN DIGIT ZERO #\x1946 ;LIMBU DIGIT ZERO #\x19D0 ;NEW TAI LUE DIGIT ZERO #\x1A80 ;TAI THAM HORA DIGIT ZERO #\x1A90 ;TAI THAM THAM DIGIT ZERO #\x1B50 ;BALINESE DIGIT ZERO #\x1BB0 ;SUNDANESE DIGIT ZERO #\x1C40 ;LEPCHA DIGIT ZERO #\x1C50 ;OL CHIKI DIGIT ZERO #\xA620 ;VAI DIGIT ZERO #\xA8D0 ;SAURASHTRA DIGIT ZERO #\xA900 ;KAYAH LI DIGIT ZERO #\xA9D0 ;JAVANESE DIGIT ZERO #\xAA50 ;CHAM DIGIT ZERO #\xABF0 ;MEETEI MAYEK DIGIT ZERO #\xFF10 ;FULLWIDTH DIGIT ZERO #\x104A0 ;OSMANYA DIGIT ZERO #\x11066 ;BRAHMI DIGIT ZERO #\x1D7CE ;MATHEMATICAL BOLD DIGIT ZERO #\x1D7D8 ;MATHEMATICAL DOUBLE-STRUCK DIGIT ZERO #\x1D7E2 ;MATHEMATICAL SANS-SERIF DIGIT ZERO #\x1D7EC ;MATHEMATICAL SANS-SERIF BOLD DIGIT ZERO #\x1D7F6 ;MATHEMATICAL MONOSPACE DIGIT ZERO )) (define (digit-value ch) (digit-value* ch zeros)) (define (digit-value* ch zeros) (if (null? zeros) #f (let* ((val (char->integer ch)) (val0 (char->integer (car zeros))) (val9 (+ val0 9))) (if (and (<= val0 val) (<= val val9)) (- val val0) (digit-value* ch (cdr zeros))))))CL provides this as digit-char-p, which is its substitute for char-numeric?.
This belongs in the (scheme char) module.
Page 4 shows a naming convention for procedure parameters:
and so on.
There is no notation convention for characters and strings. It feels a bit funny that the document uses this notation and then x, x_1, x_2 are used for reals, but then uses "char_1" and "char_2" for characters.
I think this is self-explanatory.
The term "textual port" is R6RS compatible.
Bikeshed, go with R6RS.
The standard input and output ports which current-input-port and current-output-port are initially bound to are not opened explicitly. They default to character ports. Should they be replaceable with equivalent binary ports using the following procedures?
It is an error to call either of these if the corresponding current-{input,output}-port is not the original value, or if any I/O has been performed on them, or if they cannot reasonably be treated as binary.
Ugly, but I want to be able to implement cat(1).
See BlobIoShinn, which provides the ability to read and write blobs, and simple conversions between blobs (interpreted as UTF-8) and strings.
Getting rid of file-specs was the motivation for the new binary I/O API we agreed on, but it was not made explicit in the proposal. Consequently, although all references to file-spec have been removed from the current draft, we should vote on this for completeness.
For good reasons, +nan.0 is not = to any other number, including itself. However, eqv? is about "sameness" rather than "equality".
The same proposal is that we add two clauses to the definition of eqv?, one saying that if both arguments are +nan.0, eqv? must return #t, and if one argument is +nan.0 and the other is not, eqv? must return #f. This is what R6RS specifies.
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?.
Note the second clause in the same proposal is universally supported by all implementations with +nan.0 except for SISC, which appears to have a bug (see below), so the only thing to decide is the first clause.
The following 7 implementations return #t: chez, gambit, guile, ikarus, kawa, racket, stklos.
The following 7 implementations return #f: bigloo, chibi, chicken, gauche, larceny, 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.
Since implementations currently disagree on these semantics, it may make the most sense to leave this unspecified.
Do we want to add a clause stating that all module names under the (scheme ...) name are reserved for current and future standards? Do we want to reserve the (srfi ...) names?
Note the name scheme may be changed pending the result of #237.
Several implementations provide a define-values macro. This allows cleanly writing multiple definitions with a shared state for example.
Should we have it on WG1 or not?
Enough with the syntactic sugar! Let people write their own, or refer to the large language for common macros.
eager, like delay, returns a promise object that can be forced by force, but it evaluates its argument up front (it is a procedure, not syntax) and stashes it in the promise in such a way that force can access it.
Semantically, writing (eager expression) is equivalent to writing (let ((value expression)) (delay value)).
Some debate was given as to how useful eager is - generally, if something is known in advance to be eager you don't want to make it a promise to begin with. Use cases should be provided if we want to include this.
I'm not convinced the uses for this are common enough to add it as a procedure instead of just writing (let ((value expression)) (delay value)).
They are in R6RS, apparently because they are considered more closely related to strings rather than vectors.
Note currently vectors are not self-quoting.
There's no reason they shouldn't be.
The term "scheme" is already in use in module names on some Scheme implementations. We need to pick something that nobody is using.
The term "rnrs" was used by R6RS, but this was integrated with the library versioning mechanism. It therefore may not be suitable, and either way would cause conflicts with existing R6RS modules.
Feel free to write in a name.
From Denis Washington:
Reading chapter 2 of the third draft, I was thinking: now that we have `#!fold-case` and `#!no-fold-case` and other directives might follow in WG2, wouldn't it be appropriate for section 2.3 (Other notations) to define `#!` as generally introducing a "read directive"? That would encourage implementations to use the same syntax for their own directives, which helps portability (an implementation could just ignore unknown directives which might just be used by another for optimization purposes).Note that since the only use we have alters the reader, the ! is consistent with the existing convention for !.
The procedure, as currently spec'd, may return a fraction of a second, and there should be a mention of TAI in it. Current-tai-time is redundant, since the T in TAI stands for Time (or Temps).
Implementations should be permitted to distinguish 0.0 from -0.0 in accordance with IEEE 754. 0.0 and -0.0 should be the same to = and friends, but should be distinguishable by eqv?.
Mathematically, negative inexact zero represents a number greater than the largest representable negative inexact number and less than or equal to 0. This is different from positive inexact zero, which represents a number greater than or equal to 0 and less than the smallest representable positive inexact number.
Vote yes to adapt the description of -0.0 from R6RS and include examples where appropriate.
Denis Washington said (<http://lists.scheme-reports.org/pipermail/scheme-reports/2011-August/001255.html>):
I would love to see a ticket added about possibly including (some of) the detailed "Overview of Scheme" chapter from R6RS into the report; it helps very much to understand the rest of the report and is invaluable for e.g. students. Would someone from the working group do this (provided that anyone actually agrees with me)? It would be sad if this consideration were forgotten.The "Overview of Scheme" in R6RS contains a similar introduction as in the section of the same name in R5RS, followed by a rough tutorial describing the basic syntax and data types.
This is not a normative part of the report, nor do I feel does it provide a particularly good tutorial, which should be tailored to different types of students. It just presents a watered-down version of the same descriptions provided later in the same, relatively short document.
In the string case conversion, it mentions the context sensitivity of Greek sigma: A small final sigma needs to be used when it is at the end of the word. However, there's no definition of "word", which can lead inconsistent behavior among implementations. We can refer to UAX #29, as R6RS does.
Vote uax-29 for the reference, or unspecified to leave this up to the implementation.
Should we provide the obvious way to fill part of a string or vector?
Fill-string is an abomination, fill-vector belongs in a larger vector library.
Currently this is unspecified, and different implementations behave differently. WG2 will likely provide explicit control for this, but we may want to specify the default behavior in WG1.
Vote overwrite to truncate and overwrite the existing file, or error to require an error be signalled.
This seems to be the most common behavior among implementations.
This is one of several issues raised by ModuleFactoringSummary.
This and the following items ask you to decide whether a current set of procedures under discussion belongs in the core or a separate module. The default is core reflecting the fact that R5RS had no separate modules at all.
Should the basic I/O procedures (not involving file I/O or reading or writing) be in the core or a separate module?
The I/O system is controversial, hence the complete (though unpopular) rewrite in R6RS. We should leave room for people to experiment with alternatives without them being second-class.
This is one of several issues raised by ModuleFactoringSummary (see #262).
Should interaction-environment be in the core, the REPL module, or the eval module?
interaction-environment is an abstract utility, not necessarily restricted to a traditional REPL.
This is one of several issues raised by ModuleFactoringSummary.
Should case-lambda be in the core or a separate module?
case-lambda is one of the worst things that has ever happened to Scheme. It requires a quadratic explosion in duplicate code to handle the optional parameters case, yet it strictly less powerful than alternatives such as match-lambda for more complex cases. It is only useful as a niche form for procedures whose behavior actually changes depending on the number of arguments - an uncommon and debatable type of API, which should not be encouraged.
This is one of several issues raised by ModuleFactoringSummary.
Should values and call-with-values be in the core or a separate module?
Multiple values are another wart in the language, which unecessarily complicate both the implementation and all user code which deals with HOFs.
This is one of several issues raised by ModuleFactoringSummary.
Should the Unicode normalization procedures be in the core, the char module, or their own separate module?
This is a controversial new feature, not yet implemented in any Schemes, and thus the option of remove is being added here to remove the feature altogether.
This is one of several issues raised by ModuleFactoringSummary.
Should we provide an aggregate module for the three (or four) proposed I/O modules, where (scheme io) provides all of:
I've changed my mind here. We can leave aggregate modules up to WG2.
This is one of several issues raised by ModuleFactoringSummary.
Should make-parameter and parameterize be in the core or their own separate module?
Note current-in/output/error-port are parameters, though they do not require the parameter API to be useful as is.
This is intertwined with the core language.
This is one of several issues raised by ModuleFactoringSummary.
Should define-record-type be in the core or in its own separate module?
No one thinks SRFI-9 is the one true record system, just that it's the only one we can agree on. We should leave room for other record systems, and not give this one special status.
This is one of several issues raised by ModuleFactoringSummary.
Should the Unicode character case and property utilities be in the core or their own separate module?
These require pretty large tables to load into a small implementation.
Denis Washington made the following proposal for the names of the variants of Scheme defined by WG1 and WG2:
The current draft is written in the same style and layout as all the drafts through R5RS, and by default has kept the same naming convention. Do we want to change the name?
Note the name for WG2 is beyond the scope of this ballot.
I think changing the name at this point would give the misleading impression that the new report somehow deviates from tradition even more so than R6RS.
An incomplete list of the differences between this language and the R6RS is available. Do we want to include this directly into the document? Alternately it can go into a separate document, or be included in the WG2 document.
This would be too long, and more properly belongs in WG2.
Some doubts were raised as to whether reader label cycles were allowed in quasiquote. Since cycles in code are "an error", and quasiquote is just a macro expanding into code, then this case is also an error (and thus implementation dependent).
Do we want to explicitly state that the result is an error for quasiquote? Or make a special exception and try to require handling of some cases for quasiquote? Or make no special note of this since it's already covered?
Vote note to add a note.
If we include error examples for this case, we should include one for quasiquote.
From Felix Winkelmann:
Using "\xX...;" as escape sequence is suboptimal, as it confuses syntax highlighters. I also have no knowledge of any precedent of this syntax. Also: how is this sequence handled inside "|...|"?Prior to R6RS no implementations to my knowledge used this syntax, and "\xXX" with a fixed two characters and no trailing semi-colon, as well as "\x{X...}" were used. The semi-colon specifically conflicts with the existing uses of "\xXX", although this can't represent all characters. Braces would at least allow for backwards compatibility with existing code.
Note the escapes for symbols will be the same unless someone proposed otherwise.
The current BNF for symbol syntax is rather cumbersome, having to account for the fact that +inf.0, -inf.0 and +nan.0 are numbers even though they do not begin with a numeric prefix.
A simple solution would be to use an alternative such as 0/1, 0/-1 and 0/0, respectively. These are shorter, more self explanatory, and do not conflict with the definition of symbol syntax.
Alternately we can just require a numeric prefix on the existing names.
This fits well with our definition of symbol syntax, and keeps the BNF simple and free of exceptions.
Scheme used to use #!true and #!false before abbreviating to the unfortunate #t and #f syntax, which look far too much alike.
We could add these back in as aliases, optionally without the "!" now that tokens are required to be delimited so there would be no ambiguity.
Note - this proposal is to add alternate names. #t and #f will be kept however we vote.
Most languages use true and false spelled out, and #t and #f are maddenlingly difficult to distinguish.
Previously we voted to keep the R5RS # placeholders for "unknown" digits, and leave out the new R6RS mantissa widths.
Feedback suggests that this feature is never used in R5RS programs. It was a leftover from R3RS procedures for formatting numbers when more digits of precision were asked for than were available, and also commonly used in papers on the subject of formatting numbers. These formatters are no longer in the language, and human-written code rarely if ever takes advantage of the feature, so we may want to reconsider removing it from the language.
Vote no to remove the # placeholders.
Previously we voted to keep the R5RS semantics of returning a single, unspecified value for the results of side-effecting expressions.
Some implementors have raised concerns about this. The R6RS semantics allow implementations to return an unspecified number of unspecified values, which allows for the R5RS semantics, as well as for returning zero values.
The argument is that a non-trivial amount of existing R5RS code explicitly depends on these expressions returning a single value.
The counter-argument is that using an unspecified value at all is bad style, and there is likely a large overlap between the programmers who do so and the implementations which will continue to return a single value. The hope is that code using "good style" would be portable, whereas "bad style" would continue to work on existing implementations but not be portable to others.
We should reconsider this item.