We need a VCS to keep track of changes to the standard as we start drafting it.
As per the charter, we need a module system proposal which allows sharing of code between implementations.
This is one issue where we can't default to the R5RS, since it has no module system. If we can't come to consensus, we will have to take the R6RS module system as-is.
Note the r6rs-- option is just the R6RS module system without versioning or phasing.
Rationale: R6RS-- is our best compromise and the most useful for WG1, but modules should be syntactic entities.
Given equal technical merit and compatible extensibility for WG2, should WG1 prefer SRFIs or standardized behaviors from R6RS when faced with the choice. For example, a version of syntax-violation vs. syntax-error.
This is a meta-item, to be used only as a guideline.
These were relegated to a compatibility library in R6RS. Do we want to keep them, drop them, or move them to a library?
Yes means to keep them in the core, as in R5RS, and no means to remove them entirely.
R6RS added letrec* and defined the semantics of internal define to be equivalent. Do we want to add this?
Choose letrec* just to add the syntax, define to change the behavior of internal define, or yes/both for both.
This extension allows the list arguments to be of unequal length, and stops the procedure whenever any of them run out. R5RS says the lists must be of the same length, R6RS says they should be.
Yes to allow unequal length.
This extension accepts a third argument, the equality predicate to be used. Alternatively we could use the R6RS predicates ASSP and MEMP.
New to R5RS, do we reaffirm the sometimes debated dynamic-wind?
Removing this would require a strong rationale indicating that it's fundamentally flawed.
New to R5RS, do we reaffirm multiple values, specifically the procedures call-with-values and values?
Removing this would require a strong rationale indicating that it's fundamentally flawed.
Note if these forms are removed or placed in a module, for consistency none of the core library should return multiple values (as is the case in R5RS).
Yes to keep them, no to remove them, and module to relegate them to a module.
Scheme's primitive mechanism of improper lambda-lists allows for optional arguments, but only with extra machinery. CL, DSSSL, and some Schemes provide a special word such as #!optional in lambda-lists, showing that the arguments which follow are optional and may have default values. SRFI-89 provides both optional and keyword arguments via lambda* and define* and without introducing #!foo special tokens.
Note the original ticket description mentions case-lambda, but this is easily provided as a separate module, and will be a separate item.
Student programs often want a small amount of randomness, not necessarily of very high quality. Shall we provide a simple interface to a random variables in WG1 Scheme?
Rationale: Randomness without seeds is not useful. We should have a complete, functional, but simple interface rather than one that is over done.
Pretty much all Schemes except embedded ones provide a notion of current error distinct from current output. Should this be exposed as a Scheme output port?
Should WG1 provide a module equivalent to the (rnrs files) module? This provides delete-file and file-exists?, which are pretty much necessities for any file-driven programming.
Note PortsCowan automatically includes these - voting for them here guarantees them even if not included by a specific proposal.
Should we add the 10 procedures mentioned at CompleteSequenceCowan in order to make the Scheme sequence types consistent? They are `make-list copy-list list-set! string-map string-for-each string->vector copy-vector vector-map vector-for-each vector->string`, all with the obvious interface and semantics.
R5RS requires that Scheme support five indicators for the precision of floating-point values, not only the default e but also s, f, d, and l. Only a few Schemes actually support more than one precision, so this is mostly noise. Shall we make it an optional feature?
Should we add an EXACT-INTEGER? predicate? Currently, to determine whether a number is both an integer and exact, we must test for both, which requires some hackery or poor pattern matching to optimize in existing Scheme implementations.
We would like a standard for checking function arity. SRFI-102 proposes a way to check function arity:
list?, length, equal? and other fundamental primitives may diverge when given cyclic data. In the former two cases, avoiding this is simple and not inefficient, and the equivalents are already provided in SRFI-1. In the latter case a proposal was made and rejected on the R6RS list. In the former case, R6RS seems to require list? return #f and length raise an error.
Do we want to specify the behavior when these primitives encounter cyclic data?
Options are equal? to specify equal? must not terminate on cyclic input, r6rs to specify R6RS behavior for list? and length, srfi-1 to specify the SRFI-1 semantics (where length returns #f) and equal?+r6rs or equal?+srfi-1 are options for both.
Note: I want R6RS behavior, which requires that all of list?, equal?, and length terminate and return reasonable values. I especially do not like the idea of requiring equal? to not terminate.
Should WG1 include exact-integer-sqrt from R6RS? It allows square root operations in Schemes that don't provide inexact arithmetic, and has different semantics from sqrt, as it rounds its argument down to the nearest exact square.
(exact-integer-sqrt k) => (values s r) ; k = s^2 + r
r6rs/yes for R6RS semantics, list to use a list instead of MV, or single to only return s.
Shall we add these numeric predicates defined on the IEEE floating point values from #20?
Should we allow call/cc as an equivalent to call-with-current-continuation?
In general, in places where an implict BEGIN occurs, it is possible to change this to an implicit LET-NIL and remain backwards compatible. Should we do this?
This is a meta-item to be used as a guideline, and specific places would need to be brought up for review.
R6RS provided a detailed exception system with support for raising and catching exceptions, using a hierarchy of exception types.
Do we use this, or parts of it, or a new exception system? The r6rs option is just for the core exception handling, not the conditions hierarchy.
I propose that we provide exception handling as specified in R6RS without the condition system, or that we consider the condition system separately.
Rationale: R6RS does mostly the right thing here with exceptions. The condition system could use more work, but we should leave that to someone else for now.
Do we support the near ubiquitous SRFI-23 error procedure, and if so should it use the SRFI-23 signature, R6RS, or type-dispatch on the first argument to allow both?
Note ExceptionHandlingCowan currently includes a SRFI-23 compatible error procedure.
Note: I have a problem with type dispatching on both because R6RS allows for any type of value to be the first argument to the error procedure, which can be convenient, especially with regards to strings.
Do we support string ports, as implemented by SRFI-6 or as by R6RS?
Note that currently PortsCowan provides SRFI-6 string ports.
I like the R6RS version better because it separates the port type returned from get-string-output-port and the means of extracting the data. I think this separation is good for a number of reasons, the two primary ones being that we can make it possible for an application to write to an output port without being able to extract the data from the port, easily. Secondly, that the port returned can, if desired, be identical in behavior to a normal textual output port, as opposed to forcing a different port type.
SRFI-38 standardizes the #0=(1 . #0#) shared structure notation for read/write. In the case of write, this can be expensive to compute, but otherwise the common case of the repl printing a cyclic structure results in an infinite loop.
Do we want to add support for this, as an option or separate set of procedures?
srfi-38 for separate procedures or native to require read and write to handle cyclic notation.
Rationale: This is a common extension that should be supported, as it makes the programs more reliable. It should be built in, not tacked on, so native is the way to go.
A popular extension, formalized in the R6RS, is to allow "(... <templ>)" in a syntax-rules template to be an escape for "<templ>". Do we use this, and if so what does (... <t1> <t2>) mean?
Should we have syntax-error parallel to SRFI-23 error? This is evoked when macros are expanded.
This is not something that we should include natively because the normal way to implement this is through a procedure, which does not work with non-procedural macro systems, which are the only types of macro systems on the table for WG1. We could implement it syntactically, but I think it is better to do this procedurally in WG2.
Do we keep syntax-rules in the core, relegate it to a standard module, or leave it out entirely (possibly letting WG2 specify it).
Yes to keep in core, no to remove from Scheme entirely.
R6RS introduced identifier syntax as a way to expand identifiers in non-macro positions.
Orthogonal to the overall macro system and what types of expanders are provided, do we provide a means to specify identifier syntax?
R6RS extends define-syntax to be allowed in local lexical contexts. Do we allow this as well?
R6RS adds _ as a wild-card pattern, breaking some existing R5RS macros. Do we add the _ wildcard, or leave it as a normal identifier as in R5RS?
Yes to add, no for R5RS.
As an alternative to #7, SRFI-46 proposed allowing an optional ellipse specified as an identifier before the literals list in syntax-rules:
(syntax-rules ::: () <ellipse now represented as ::: instead of ...>)
Do we allow this?
This is no longer necessary with the introduction of a proper module system. It is better to do this through the module system than to complicate the syntax of syntax-rules.
Rationale: So long as this doesn't break backwards compatibility, it is useful, but I question how useful.
SRFI-46 and R6RS both allow a fixed number of tail patterns following an ellipsis in a syntax-rules pattern:
(P1 ... Pk Pe <ellipsis> Pm+1 ... Pn)
R6RS further allows dotted tail patterns
(P1 ... Pk Pe <ellipsis> Pm+1 ... Pn . Px)
where Px only matches a dotted list.
Do we allow either or both of these extensions?
Rationale: These are very useful.
R6RS provides support for inexact infinities and NaN objects. Do we keep these, and if so do we use the same literal syntax and arithmetic as in R6RS?
Yes to keep them with the same syntax and semantics of R6RS, or write in a separate proposal for some other syntax/semantics.
R6RS provides libraries for limited type arithmetic on fixnums only and flonums only (i.e. fx+, fl* etc.). Do we want these?
R6RS introduced the concept of mantissa widths as an alternative to the R5RS #s in numbers. Do we want either or both of these?
Does the reader fold case by default, and if so how?
Yes to fold-case (R5RS) no to preserve case (R6RS), additional votes to come later from specific proposals.
Rationale: Case sensitivity is more popular, let's go with it. Otherwise, let implementations determine it.
R6RS greatly extends the list of character names, as well as allowing #\xNN numeric escapes for characters. Do we allow any or all of these names?
mnemonic for #\tab and friends, numeric for #\xNN as in R6RS, and yes/both for both.
The exact list of added names is to be decided later.
R6RS allows [] brackets as identical to parenthesis, with the condition that they must balance. Do we accept this extension, propose some other use for brackets, or leave them unspecified?
Yes for R6RS, no for R5RS, or write in a proposal for some other meaning for brackets.
R6RS provides support for #; nested sexp comments, and #| ... |# nested block comments. Do we include either or both of these?
Rationale: These are very useful.
R6RS provides character escapes in symbols of the form \xnnnn;, where nnnn is 1-5 hex digits. Do we accept this extension? Do we also allow |...| to escape a whole symbol or a part of one?
In all existing standards pipes are reserved and the |...| syntax is unspecified. In most implementations it's recognized, but there are at least a few implementations where pipes are normal character constituents.
R6RS provides character escapes in strings of the form \xnnnn;, where nnnn is 1-5 hex digits, as well as \n, \t etc. C-like escapes for common control characters. Do we accept either or both of these extensions?
R6RS provided operations to alter the case of strings and characters (upcase, downcase, titlecase and foldcase) using locale-independent Unicode mappings. Do we provide equivalent mappings?
Note in a Unicode implementation individual character casings are incomplete, and string case is not defined as a simple mapping of case over the constituent characters.
Note UnicodeCowan currently provides mappings at both levels.
R6RS provides procedures to explicitly convert strings back and forth between the four Unicode normalization forms.
The previous phrasing of this option was overly vague, referring to "any form of normalization." I've had to treat yes votes as undecided for lack of a better default. If you voted yes before please choose one of the following options or write in your own proposal.
Note UnicodeCowan currently provides specific normalization procedures.
Rationale: Keep the complexity of unicode down.
R6RS suggests string-ref and string-set! work in O(1) time, implying strings are implemented as character arrays. Do we reaffirm this?
Yes for required constant time.
R5RS said almost nothing about character sets. R6RS specified full Unicode. Do we specify a character set, or limit the options in any way?
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Several SRFIs, R6RS, and most Scheme implementations support some sort of uniform packed integer vectors. In particular, these are necessary for efficient binary I/O, and for memory mapping, so WG2 will certainly want them.
Do we provide a syntax and basic API for these in WG1?
I am in favor of John Cowan's small WG1 proposal provided that we change the term "blob" to "bytevector".
Most Scheme implementations provide some form of dynamic bindings such as those provided by SRFI-39 parameters.
I find very little of use for a parameter that is not mutable, so I can't see a lot of benefit to Cowan's proposal, of immutable parameters, even if we provides some way to mutate them through parameterize. I disagree with the ParametersSnellPym proposal because it suggests to different behaviors for parameters based on whether they are mutated by themselves or with parameterize. I believe that we should have mutable parameters, and that there should not be a difference whether they are mutated by parameterize or not. I think that we should specify that parameters are thread parameters by default in the case of threads, but I am more than happy to have them mutable and have their thread behavior undefined. Programs written in WG1 will continue to run in WG2 in either case. The main issue is whether a parameter based library imported into a WG2 threaded environment will be able to know what is happening. I'd prefer to avoid it being able to tell, which means that I would like to have the threads have their own state. I am assuming of course that a form of global parameters will be made available.
I should develop a proposal on this.
Do we support any means of creating disjoint user-defined types, such as in SRFI-9, SRFI-99 or the R6RS record system?
R6RS and SRFI-69 both provide hash-table interfaces. Do we provide either of these, or try to provide some primitives on which efficient hash-tables can be implemented?