Version 8 (modified by alaric, 6 years ago) (diff)

A bit more thinking


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WG1 Ballot Items To Finalize by July 1st

Previous Undecided and Re-opened Ballot Items

#32 user-defined types

Do we support any means of creating disjoint user-defined types, such as in SRFI-9, SRFI-99 or the R6RS record system?

WG1 voted srfi-9 before. New arguments against filter constructors were raised, so the ticket was re-opened.


#28 Binary I/O ports

Do we provide any binary input or output ports, and if so how do we construct them and operate on them? Can binary and textual operations be mixed on the different port types?

BinaryPortsCowan provided binary port operations, being a mild revision of the relevant parts of PortsCowan. It has been removed by Cowan in favor of PortsShinn.

PortsShinn provides binary port operations, with similar operations to BinaryPortsCowan but keeping the binary/textual ports disjoint.

R6RS provides an entirely new I/O system, as well as a separate R5RS-compatible I/O system.

The withdrawn SRFI-91 provides yet another I/O system supporting binary ports.

Note this item as well as #29 and #31 specify semi-orthogonal aspects of I/O systems which are typically specified together by individual proposals. If the same proposal doesn't win for all three, the aspects will be merged as needed.

WG1 voted weakly in favor of PortsCowan before.

#83 Auxiliary Keywords

In R6RS auxiliary keywords (such as else in cond and case forms) are explicitly exported from the (rnrs base (6)) library. Do we want to bind and export these from the core library?

If else is bound in the default module, then it must be imported at the call site whenever using it in cond or it won't match hygienically.

If else is not bound in the default module, then it must not be bound or imported at the call site whenever using it in cond or it won't match hygienically.

Another option is to specify for cond and case that they match the else identifier literally, ignoring any hygiene. This breaks compatibility with R5RS and R6RS.

WG1 voted unbound previously. New issues were brought up on the list so the ticket was re-opened.


  • Options: bound, unbound, unhygienic, undecided
  • Default: unbound
  • Preferences: bound, unbound, unhygienic

#3 module naming convention

We need a naming convention for the core modules and standard libraries of the new module system.

The existing break down is based on John Cowan's earlier proposal of factorings in items #71, #72, #73, #74, #75, #76, #77, as well as an I/O module breakdown in PortsCowan. There have been various tickets proposing changing this, so we are re-opening the ticket.

New Ballot Items

WG1 - Core

#85 Blobs, bytevectors, byte-vectors, octet-vectors, or something else?

Now that we have blobs, we have to decide what to call them. R6RS uses bytevector, SRFI-4 and SRFI-68 uses u8vector, while the original WG1 proposal used blob (which is therefore the default).

  • Options: blob, bytevector, byte-vector, u8vector, octet-vector, undecided
  • Default: blob
  • Preferences: blob, u8vector, bytevector|byte-vector|octet-vector

I think it's important to keep blobs distinct from typed arrays. A blob is a region of memory; u8vectors are a particular interpration thereof. Blobs may be measured in bytes, but that's just due to the granularity of access - they aren't necessarily composed of independent u8s (they might be composed of u16s, or floats, or a complex structure).

However, if we have to conflate them, I'd rather go with SRFI-4 names.

#118 Simple literals must be explicitly delimited.

In R5RS syntax such as #t#f is left unspecified - some readers may parse this as the true literal followed by false. R6RS requires identifiers, characters, booleans, number objects, and . to be terminated with a "delimiter" or by the end of input.


  • Options: delimited, unspecified, undecided
  • Default: unspecified
  • Preferences: delimited,unspecified

#119 Whether to treat # as a delimiter.

In R5RS foo#f is a valid identifier, whereas R6RS requires # to act as a delimiter, so that this would parse as the identifier foo followed by the false literal.

  • Options: delimiter, no, undecided
  • Default: no
  • Preferences: no,delimiter

#123 Extend unquote and unquote-splicing to multiple arguments

This is a change also made by R6RS (and CL).


  • Options: multiple, single, undecided
  • Default: single
  • Preferences: multiple

#124 Nested quasiquote semantics


  • Proposals:
    • r5rs: unspecified
    • r6rs: strict and multiple (implies multiple for #123)
    • chicken: strict at level 0 (option 2 in second reference)
    • strict: strict at all levels (R6RS with single for #123)
  • Options: r5rs, r6rs, chicken, strict, undecided
  • Default: r5rs
  • Preferences: r6rs

#125 Allow procedures not to be locations (making EQV? unspecified in some additional cases)

This is a change also made by R6RS, specifically:

A quasiquote expression may return either fresh, mutable objects or literal structure for any structure that is constructed at run time during the evaluation of the expression. Portions that do not need to be rebuilt are always literal

  • Options: r6rs, r5rs, undecided
  • Default: r5rs
  • Preferences: r6rs

#126 Partly specify the mutability of the values of quasiquote structures

This is a change also made by R6RS.

  • Options: r6rs, r5rs, undecided
  • Default: r5rs
  • Preferences: r6rs

#127 Specify the dynamic environment of the before and after procedures of dynamic-wind

R5RS is slightly ambiguous, saying

BEFORE is called whenever execution enters the dynamic extent of the call to THUNK and AFTER is called whenever it exits that dynamic extent.

without saying clearly whether before and after themselves are called before or after the dynamic extent is entered or exited.

  • Proposals:
    • outside: called outside the dynamic extent (R6RS)
    • inside: called inside the dynamic extent
    • unspecified: R5RS
  • Options: outside, inside, unspecified, undecided
  • Default: unspecified
  • Preferences: outside,inside,unspecified

#135 let-values and let*-values

These R6RS procedures were part of #77 (modularization of multiple values), but were never explicitly voted up or down by WG1, so I'm opening a new ticket for them.

  • Options: yes, no, module, wg2, undecided
  • Default: no
  • Preferences: yes,no

#137 Current-seconds semantics still open

In issue #70, WG1 voted to make current-seconds an optional procedure, but there is no guidance about what it returns.

If we choose to specify this further, the big question is whether or not to include leap seconds - i.e. do we specify it as TAI or POSIX time (the choice of the epoch itself is less controversial and defaults to the POSIX epoch). TAI time has the advantage that it measures real, unambiguous time, and two calls to current-seconds more than a second apart are guaranteed to actually differ. POSIX time has the advantage of bug-for-bug compatibility with POSIX systems - the times are ambiguous, but they already have to deal with that.

The other issue is whether to return an integral number of seconds and lose the ability to specify subsecond real times, or return an inexact real (flonum) number of seconds and have to deal with variable precision depending on the date.

TimeCowan is equivalent to the posix-integer option, and in addition changes the name to current-posix-second.

  • Proposals:
    • cowan: TimeCowan
    • posix-integer: POSIX time as an exact integer value
    • posix-flonum: POSIX time as an inexact real value
    • tai-integer: TAI time as an exact integer value
    • tai-flonum: TAI time as an inexact real value
  • Options: cowan, unspecified, undecided, none
  • Default: unspecified
  • Preferences: tai-flonum,posix-flonum,tai-integer,posix-integer

I prefer TAI over POSIX as I hate being bug-compatible with past mistakes. However, regarding the potential implementation difficulties of TAI on a POSIX underlying system, I'd like to shove that under the unavoidable carpet of "Yeah, but implementation accuracy isn't particularly well defined" - so although I'd like current-seconds to monotonically and continuously increase about once a second, the implementation is quite free to return a time counter initially seeded from a POSIX clock without knowing how many leap seconds are in there, and just be inaccurate by a few seconds. As it might simply be wrong anyway due to a bad clock.

#147 Allow literal file spec lists in include and include-ci

This could allow implementation-specific extensions to support files don't have character-string names. On the other hand, such names probably shouldn't be used as source files, and there are other ways to support this.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

The way we specify filenames should be consistent across Scheme.

#148 Allow include-ci at top level

Currently include-ci is allowed as a module declaration but not at top level, as include is.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes,no

#149 blob ports

We've voted to add string ports, which are character ports backed by Scheme strings. Since we have blobs another potential extension is blob ports, which binary ports backed by blobs. These are described in PortsCowan, but it's unclear if they were specifically voted for or against in the previous ballot.

  • Options: cowan, none, undecided
  • Default: none
  • Preferences: cowan

#150 cond-expand at top level

Currently cond-expand is only valid as a module declaration. Should we allow it at top level in a program?

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#153 Renaming blob procedures

The blob procedures don't follow the same system as the rest. I propose these changes:

copy-blob => blob-copy
copy-blob! => blob-copy!
partial-blob => blob-copy-partial
copy-partial-blob! -> blob-copy-partial!

Note this is modulo the choice of "blob" or "bytevector" or whichever.

  • Options: new, original, remove, undecided
  • Default: original
  • Preferences: new,original,remove

#154 Physical newline in a string equivalent to \n (that is, U+000A)

R5RS leaves this situation undefined, but R6RS, CL, and most languages that allow it (C does not) treat physical newline and escaped newline as equivalent, even if the local representation of line endings is \r\n or U+0085 or what not. Another possibility is to treat string literals broken across lines as errors.

  • Options: unix, local, error, unspecified, undecided
  • Default: unspecified
  • Preferences: unix,error,unspecified,local

#155 Make recursively defined code an explicit error

Allowing examples like these will make code-walkers (including compilers and interpreters) excessively complicated:

#1=(begin (display #\x) . #1#)

(lambda #2=(a b c #2#) ...)

(+ . #3=(1 2 3 . #3#))

  • Options: error, unspecified, undecided
  • Default: unspecified
  • Preferences: unspecified,error

#156 Replace "an error is signalled" with "an implementation-dependent object is raised as if by raise"

The following situations are described in draft 1 (and R5RS) with "an error is signalled":

  1. The file-spec given to call-with-input-file, call-with-output-file, open-input-file, or open-output-file represents a file that cannot be opened.
  1. An end of file is read from a port by read after the beginning of an object's external representation, but the external representation is incomplete and therefore not parsable.

I propose that in both cases the implementation be required to raise an exception as if by applying raise (that is, non-continuably) to an implementation-defined object, which means it can be caught by the R7RS exception system. Note that there is no requirement to create a fresh object.

  • Options: signal, unspecified, undecided
  • Default: unspecified
  • Preferences: signal,unspecified

#162 Remove DELAY and FORCE altogether

They are present in R4RS and R5RS, but not IEEE Scheme (which is our baseline). There are problems with a straightforward implementation that SRFI 45 fixes, but we voted down SRFI 45. Given that, we should consider removing them from the standard altogether. (Of course this does not mean compliant implementations can't provide them, it just means they won't be in a standard module.)

Since the inconsistency was raised and people are going so far as to remove these, we can entertain votes for SRFI-45's lazy again.

  • Options: remove, keep, lazy, undecided
  • Default: keep
  • Preferences: remove,keep,lazy

#164 Meaning of char-numeric?

The current draft, like R6RS, defines char-numeric? according to the nonexistent Unicode Numeric property. That has to be fixed. Options:

  1. Any. char-numeric? returns #t if the character's Numeric_Type property value is other than None. This means that many hanzi are both alphabetic and numeric.
  1. (Omitted, because it does not preserve IEEE Scheme)
  1. ASCII. Define char-numeric? to return #t only for ASCII 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. This retains compatibility witht R5RS, and we can still use char-numeric? to parse numbers, and safely use (- (char->integer c) (char->integer #\0)) to obtain the digit value the character represents. (Note: R5RS programs that use char-numeric? to parse numbers will break if we adopt the current draft's definition of char-numeric?). Gauche, Gambit, and Chicken (without the utf8 egg) work like this.
  1. Digit. Define char-numeric? as equivalent to the Numeric_Digit property (general category value of Nd). Guile 2.0, Kawa, Larceny, Ypsilon, Mosh, and IronScheme? work like this.
  1. Number. Define char-numeric? as equivalent to the Number property (general category values of Nd, Nl, No). Scheme48, Chez, and Ikarus work like this.
  • Options: any, number, digit, ascii, undecided
  • Default: ascii
  • Preferences: digit,any|number,ascii

#166 Add predicate and accessors for error objects

(Email from Vincent Manis)

Problem: It's impossible to write a portable error handler that writes out the message and irritants that were passed to error.

This comes about because error creates an "implementation-defined object". I would assume that this hides the whole exception class hierarchy a WG2 implementation might provide. Since the message and irritants arguments to error are presumably living in this implementation-defined object, it should be simple enough to provide accessors to extract them, so that the above "portable error handler" can be written.

Suggestion: Add the following procedures:

(error-object? object)

Returns #t if object is something created by error, #f otherwise. Any constraints on type disjointness are up to the implementation.

(error-object-message object)

Returns the message of object.

(error-object-irritants object)

Returns a list of the irritants of object.

  • Options: manis, none, undecided
  • Default: none
  • Preferences: manis

#167 Add constructor for error objects

(Email from Vincent Manis)

Problem: Raising arbitrary objects as exceptions has been found to be nasty in some other languages (Python and C++ in particular).

This one is a tad speculative, but I'm reluctant to encourage people to write things like (raise 4), because of course it doesn't respect any module boundaries. I think the intent with the descriptions of raise and raise-continuable was to allow exception hierarchies to be added in WG2 without constraining them here. I would suggest adding a new procedure:

(make-error-object message obj ...)

to creates the implementation-defined object error is supposed to create, and adding a sentence to the raise and raise-continuable entries that says "The effect of applying this procedure to an object not created via make-error-object is implementation-defined." This allows WG2 to do what it wants regarding exception objects, and to limit the types of exception objects allowed, without breaking anything in WG1. Error can be defined as:

 (define (error message . objs)
   (raise (apply make-error-object message objs)))
  • Options: manis, none, undecided
  • Default: none
  • Preferences: manis

#169 Add standard-*-port procedures

These return the initial values of the corresponding current-*-port procedures, and can be used to access the implementation-provided standard input, output, and error streams.

  • Options: r6rs, none, undecided
  • Default: none
  • Preferences: none,r6rs

I wince at the sandboxing implications. Code run with current-*-port parameterised shouldn't be able to get hold of the standard ports again. If you want to keep the original values, do so explicitly in your own code.

#171 Duplicate identifiers in define-record-type

What happens if define-record-type is specified with two fields that have the same accessor identifiers provided for both fields? More generally, we need to say what happens when any two identifiers are non-unique.

This ticket deals specifically with the situation where two identifiers (accessors or mutators) of two field clauses in a define-record-type form are identical. This is not meant to address field names and what happens or what it means if the field names are symbolically equivalent but lexically distinct.

  • Options: error, unspecified, undecided
  • Default: unspecified
  • Preferences: error,unspecified

#173 Unifying BEGINs

In R5RS, there are three kinds of BEGINs:

1) All subforms are expressions; this can be used wherever an expression can be used. (4.2.3)

2) All subforms are definitions; this can be used wherever an internal definition can be used. (5.2.2)

3) Subforms can be definitions or expressions intermixed in any order; this can be used only at top level. (In R7RS we extend this to module top level as well). (5.1)

In particular,

(define (x)
 (define y 32)
   (define z 45)
   (set! y z))

is not licensed by any of these provisions, and consequently is not valid R5RS Scheme. Nevertheless, all of my usual Schemes accept the above definition except Scheme48/scsh and SSCM -- actually, SSCM fails when you invoke x rather than when you define it. So I'm proposing that we unify them for R7RS.

  • Options: cowan, r5rs, undecided
  • Default: r5rs
  • Preferences: cowan,r5rs

#174 Safe uses of multiple values

Currently, uses of values where the values are discarded anyway is illegal, but all the usual Schemes except SCM and SSCM accept them (I tested with begin). Should we go with something close to the R6RS wording?

"The continuations of all non-final expressions within a sequence of expressions, such as in lambda, begin, let, let*, letrec, letrec*, case, and cond forms, take an arbitrary number of values."

The definition of begin would need to change too:

(define-syntax begin
  (syntax-rules ()
    ((begin exp)
    ((begin exp1 exp2 ...)
         (lambda () exp1)
       (lambda args
         (begin exp2 ...))))))
  • Options: safe-values, r5rs, undecided
  • Default: r5rs
  • Preferences: safe-values,r5rs

#45 Record-let syntax and semantics

(record-let <record-data> ((<variable> <field>) ...)

Where each <variable> is filled with the corresponding data <field> from <record-data> as in a <let> expression, then the <body> is evaluated with these bindinds added and last expressions is returned. It is an error if the <record-data> does not contain corresponding <fields>.

Notice that this works directly on the data itself and that the data may contain more fields than the one cited in the record-let expression allowing code to be reused for inherited records.

Do we need to be able to check at runtime if a given record data has a given field ?

  • Options: record-let, none, undecided
  • Default: none
  • Preferences: none

This can just be a macro that expands: (record-let foo ((a foo-a) (b foo-b)) (list a b)) into (let ((a (foo-a foo)) (b (foo-b foo))) (list a b)), can't it? I see no need for magic low-level access to record internals, which would unhappily restrict it to actual records anyway (so I'm a bit queasy about the name). (record-let foo ((a car) (b cdr)) ...) would be useful in its own right.

#172 Multiple returns from map

R6RS specifies that map does not mutate previous results if there are multiple returns from map. Should we include this language?

  • Options: r6rs, unspecified, undecided
  • Default: unspecified
  • Preferences: r6rs

#178 Shadowing with internal definitions

From Andre Von Tonder:

On p 19, some shadowing problems that would break lexical scope are declared to be errors. However, I believe there are other examples that shold be errors that are not covered by the report. In R6RS a more general criterion was used - please see R6RS for details. Here is an example that does not violate the WG1 report but should be an error becasue it violates lexical scoping. It does not violate the WG1 criterion because the meaning of x is not needed to determine whether (foo x p ) is a definition.

    (let ((x #f))
      (let-syntax ((foo (syntax-rules (x)
                          ((_ x y) (define y 'outer))
                          ((_ _ y) (define y 'inner)))))
        (let ()
          (foo x p)
          (define x #f) ;; this should be an error because
                        ;; it shadows the previous line where
                        ;; x has already been used in its outer sense
                        ;; during expansion

Here is another example that WG1 allows but that would cause violation of lexical scoping, because the macro would be evaluated first and treat ... as a placeholder in a region where it is shadowed to be the variable bound to 1:

    (let ()
      (define-syntax list-macro
        (syntax-rules ()
          ((_ x ...) (list x ...))))
      (define ... 1)    ;; This shadows ... in previously expanded macro
                        ;; body and will be a violation of lexical scoping
      (list-macro 1 2)) ;; if the last line evaluates to (1 2)

OTOH, it is unclear to me if WG1 allows this or not.

    (let ((x #f))
      (let-syntax ((foo (syntax-rules (x)
                          ((_ x y) (define y 'outer))
                          ((_ _ y) (define y 'inner)))))
        (let ()
          (define x #f)
          (foo x p)
  • Options: r6rs, r5rs, tonder, undecided
  • Default: r5rs
  • Preferences: r6rs

WG1 - Modules

#112 REPL redefinitions

R5RS leaves unspecified the semantics of redefining a standard binding in the REPL. Do we want to specify semantics, or some set of allowed behavior for this in the WG1 standard?

REPLs may allow redefinition. The sixteen cases that occur are redefining to/from syntax/non-syntax locally/imported, and the issue is what happens to previous references to the definition. The general possibilities are:

  1. redefinition signals an error
  2. previous references are overridden (generally not possible if it the previous definition was syntax)
  3. previous references are preserved (indicating a new binding was created, often preferred if replacing non-syntax with syntax to avoid runtime errors)
  4. the semantics are left unspecified

So all 64 combinations for these 4 values in the following 4x4 matrix are feasible:

From/To? import import syntax define define-syntax
import ? ? ? ?
import syntax ? ? ? ?
define ? ? ? ?
define-syntax ? ? ? ?

Not all 64 combinations necessarily make sense. The default from R5RS is "unspecified", which means all 16 values are unspecified. Note in most implementations there is no such thing as a "reference" to existing syntax, since macros are expanded once, but this is not the case for SCM or Wraith Scheme.

  • Proposals:
    • override: override for all 16 values (non-syntax to syntax can break closure references)
    • preserve: preserve for all 16 values (must always create a new definition, not mutate, contrary to most implementations)
    • common: most common behavior among implementations - override, except preserve for non-syntax to syntax
    • simple: override, except unspecified for non-syntax to syntax
    • dynamic: override, except unspecified for syntax to anything (compatible with SCM/Wraith)
  • Options: override, preserve, common, dynamic, unspecified, undecided
  • Default: unspecified
  • Preferences: unspecified

I think REPL semantics should be left quite open to implementation variation. Standardising code written in files is what's needed for portability!

#132 Imports override previous imports?

The current draft describes importing different bindings for the same identifier as "an error." R6RS explicitly requires this to signal an error. Do we want to change this?

This ticket refers only to modules - the top-level semantics are decided in ticket #112.

  • Options: override, preserve, error, unspecified, undecided
  • Default: error
  • Preferences: error,override,unspecified,preserve

#160 Interleaving of imports and code in a module


   (module (name)
     (begin c1 ...)
     (import (A))
     (begin c2 ...)
     (import (B))
     (begin c3 ...))

the intention, reference implementation, and specification from Scheme48 on which the syntax was based say that all imports establish the initial environment and then the code is expanded in order, but interleaving the imports is conceivable.

  • Options: shinn, interleave, unspecified, undecided
  • Default: shinn
  • Preferences: shinn,interleave,unspecified

#163 Allow modules at the REPL?

Should users be allowed to enter a module form at the REPL?

Note that there are actually many varying approaches to generating moduls at runtime, and Scheme48 and Chibi use an out-of-band REPL operation to create new modules, leaving the module binding open.

  • Options: yes, no, unspecified, undecided
  • Default: no
  • Preferences: unspecified,yes

See my earlier point about REPLs being implementation-specific.

#141 What are the semantics of modules with respect to separate compilation?

ModulesShinn says that the bodies of libraries are evaluated before any of the bodies of the importing library; does that include, eg, "at compile time" rather than at "run time"? It's not clear.

  • Options: compile-time, unspecified, undecided
  • Default: undecided
  • Preferences: unspecified

Compile time and run time are difficult to precisely define, without limiting yourself to certain classes of implementations.

#158 mutating imports

Currently the semantics of calling set! or define on an imported binding is undefined. Do we want to specifically make this an error?

  • Options: error, allowed, unspecified, undecided
  • Default: unspecified
  • Preferences: error,unspecified,allowed

Immutability of imported bindings is necessary for mutability analysis in the presence of separate compilation - which is a very important optimisation in Scheme (as it lets you avoid a LOT of indirection).

#159 base environments

What is the base environment provided by the repl, scripts, and the result of (scheme-report-environment 7)?

The intention was the base script environment was empty, scheme-report-environment was (scheme base), and repls were an implementation-defined superset thereof, but there are other options and we need to clarify this.

  • Options: shinn, undecided
    • shinn: intention as described above
  • Default: shinn
  • Preferences: shinn

#161 module argument to eval

It would be useful to allow modules as an argument to eval in addition to environments. This could be done with a special syntax, or just the module name as a list.

R6RS provides a procedure environment which just takes a list that looks like an import spec an generates the corresponding environment.

  • Options: r6rs, none, undecided
  • Default: r6rs
  • Preferences: r6rs

#139 exit

The ballot statement for #62 said we had voted for exit when we voted for ModulesShinn, but that page doesn't mention exit. So we need to vote on it.

  • Options: yes, no, undecided
  • Default: yes
  • Preferences: yes

#144 strip prefix on import

I'm thinking that for importing code that defines its external symbols as foo:this, foo:that, and foo:tother, there should be a type of import clause that strips a specified prefix from imported symbols. This is equivalent to renaming on import or renaming on export, but less painful, in the same way as the prefix import clause does.

Specific proposal: (strip-prefix <import-set> <prefix-identifier>).

  • Options: yes, no, undecided
  • Default: no
  • Preferences: no

Why not just fail to put the prefix on in the first place?

WG1 - I/O

#133 Provide read-line

This is an R6RS procedure that was part of PortsCowan, but never explicitly voted up or down by WG1. It reads a single line up to a line delimiter from a given port (the current input by default) and discards the line delimiter.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

This is just far too useful in practice...

#170 Add with-error-to-file procedure

Since we now have current-error-port, arguably we should have with-error-to-file for completeness.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#176 Are string ports exclusively character ports?

From scheme-reports discussion list, by John Cowan:

Jeronimo Pellegrini scripsit:

According to Section 6.7.1, "Conversely, not all character ports are binary ports -- for example, the /string ports/ discussed below". It is not really clear to wether the document *requires* string ports not to be binary or if it was just an example of a port that *could* be character but not binary.

I haven't thought about it, but I guess it *could* be the latter, if the environment provides a default encoding for string ports.

  • Options: character-only, unspecified, undecided
  • Default: unspecified
  • Preferences: unspecified

#177 Distinguish file and string ports?

Should there exist predicates that identify string and file ports?

  • Options: string-port?, file-port?, both, neither, undecided
  • Default: neither
  • Preferences: neither,both

#131 Output procedures return value

Output procedures (display, write, newline) currently return unspecified value, do we wish to make them return something (like in case of an error) or not?

Need proposals.

  • Options: r5rs, undecided
  • Default:
  • Preferences: r5rs

#134 Provide flush-output-port

This is an R6RS procedure that was part of PortsCowan, but never explicitly voted up or down by WG1. It flushes implementation output buffers on the specified port, the current output port by default.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes,no

WG1 - Numerics

#117 Real numbers have imaginary part #e0

In R6RS, a complex number with imaginary part 0 is only real if the imaginary part is an exact 0. In R5RS, this was not true, and the requirement was simply that (zero? (imag-part Z)) be true.

  • Options: exact-only, any-zero, unspecified, undecided
  • Default: any-zero
  • Preferences: any-zero

#120 Define the semantics of the transcendental functions more fully

R6RS has an extended description of the transcendental functions. Do we want to include this?

TODO: explain the exact diff, why it is desirable, and whether any reasonable alternatives are possible.


  • Options: r6rs, r5rs, undecided
  • Default: r5rs
  • Preferences: r6rs

#121 The semantics of expt for zero bases has been refined

This is a change also made by R6RS.

R5RS says:

Returns z1 raised to the power z2. For z1 /= 0, z1z2 = ez2 log z1; 0z is 1 if z = 0 and 0 otherwise.

R6RS says:

Returns z1 raised to the power z2. For nonzero z1, this is ez2 log z1. 0.0z is 1.0 if z = 0.0, and 0.0 if (real-part z) is positive. For other cases in which the first argument is zero, either an exception is raised [...] or an unspecified number object is returned.

  • Options: r6rs, r5rs, undecided
  • Default: r5rs
  • Preferences: r6rs

#122 Make infinity, NaN, and -0.0 semantics (when supported) consistent with IEEE 754

R5RS does not explicitly describe these values. We have to decide whether to require that, if an implementation provides any of these values, they must be consistent with IEEE 754.

R6RS both requires these values and requires they be consistent with IEEE 754.

  • Options: ieee-754, unspecified, undecided
  • Default: unspecified
  • Preferences: unspecified,ieee-754

IEEE 754 is a good standard, but I think conforming with it should be optional for implementations

#175 Control of significant digits or decimal places in NUMBER->STRING

Vincent Manis pleads for a way to write numbers with a specified precision:

I (Alaric Snell-Pym) wondered if this should be done via NUMBER->STRING or via an optional extra argument to ROUND etc specifying a precision, as a number like 0.01 to get two decimal places. How to provide significant figures rather than DP without introducing a base-10 dependency is left as an exercise to the reader (as is the task of deciding if I'm mad for not wanting a base-10 dependency)

  • Options: manis, none, undecided
  • Default: none
  • Preferences: manis

#138 DivisionRiastradh domain

Zero as a divisor aside, what should the domain of the proposed procedures be?

  1. Any real numbers?
  2. Integers only?
  3. Exact integers only?
  • Options: reals, integers, exact-integers
  • Default:
  • Preferences: integers,exact-integers

#217 DivisionRiastradh exactness preservation

What about exactness preservation?

  1. Not exactness preserving
  2. Exactness preserving unless the implementation can prove that an inexact argument can't affect the result (as in the case of an exact zero dividend and an inexact divisor)
  3. Exactness preserving in all cases
  • Options: not-exactness-preserving, exactness-preserving, exactness-preserving-unless
  • Default:
  • Preferences: exactness-preserving-unless

#140 Removing quotient, remainder, modulo

Are we removing the IEEE Scheme functions quotient, remainder, and modulo from WG1 Scheme? If so, we need a special justification, due to the charter text:

Existing features of IEEE Scheme may be removed only if a strong case can be made that they are fundamentally flawed. Insofar as practical, the language should be backwards compatible with the IEEE standard, the R5RS standard, and an appropriate subset of the R6RS standard.

Here's what DivisionRiastradh says:

Unfortunately, most programming languages give nondescript names such as DIV(IDE), QUOT(IENT), MOD(ULO), and REM(AINDER) to these operations. The language should make clear to programmers what division operations their programs are performing, especially when negative dividends and divisors can arise, but perhaps may not often arise during testing.


The R5RS gives the names quotient and remainder to the truncating division operator pair, and the name modulo to the remainder half of the flooring division operator pair. For all these three procedures in the R5RS, the dividend may be any integer, and the divisor may be any nonzero integer.

On the other hand, we may prefer relegating them to a backward-compatibility module.

Vote "yes" to keep, "no" to remove, and "module" to relegate to a module.

  • Options: yes, no, module, undecided
  • Default: yes
  • Preferences: yes

I'd love to see them removed to make Scheme more consistent, but in hindsight, it's a petty incompatibility with existing code.

#151 Extend finite? and nan? to non-real values

R6RS specifies the domain of finite? and nan? as the real numbers only. I propose that finite? return #t on a non-real value iff both the real part and the imaginary part are finite and not +nan.0, and that nan? return #t on a non-real value iff either the real or the imaginary part is +nan.0.

  • Proposals:
    • cowan: the above description
  • Options: cowan, unspecified, undecided
  • Default: unspecified
  • Preferences: cowan

#152 exact-integer-sqrt inconsistent with multiple values module

R5RS does not actually specify any procedures which return multiple values, and so the decision to separate multiple values to a module was reasonable. However, we also voted to make exact-integer-sqrt, which is in the base module, return multiple values, namely the root and the remainder. That would make the procedure useless unless multiple values are provided.

We can either make multiple values not a module, make exact-integer-sqrt return a list (or single integer) rather than multiple values, relegate exact-integer-sqrt to a new module, remove it altogether, or do nothing and leave the inconsistency.

  • Options: values-in-core, return-list, return-pair, return-root-only, new-module, remove, nothing, undecided
  • Default: nothing
  • Preferences: values-in-core, new-module, return-list|return-pair, return-root-only, remove|nothing

#180 Make case and cond clauses into bodies

Andy Wingo suggests: make the clauses in case and cond forms (without =>, naturally) be BODY instances, to allow them to have definitions. It is well defined AFAIK, and costs nothing.

The counter-argument is that it doesn't "look" like the sort of place definitions are allowed.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#181 Add WHEN and UNLESS to the base module

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#182 Add WHILE and UNTIL

These trivial syntaxes add familiarity for new Scheme programmers coming from other languages, as will almost always be the case. LOOP is too big and named-LET too alien.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: no

named-let is a good thing to learn!

#183 Escaped newline removes following whitespace?

Andy Wingo suggests the R6RS handling of escaped embedded newlines:

    "asdadf \

in R6RS has the same meaning as "asdf asdfadf". It allows you to nicely indent strings that you need to line-break for width. I suggest that the production


within string literals be elided.

Note an alternate method for handling embedded strings with nice indentation is scribble syntax.

We voted on various string syntaxes previously but did not specifically propose this R6RS extension. We should have a rationale if we don't follow it.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#184 Require CHAR=?, STRING=? etc. to accept arbitrary numbers of arguments?

R5RS makes a point of specifying that supporting more than two arguments is optional. (Everything not explicitly mentioned is optional, so this may have significance.) R6RS requires accepting 2 or more arguments. Currently Racket, Gambit, Guile, Chez, Ikarus, Larceny, Ypsilon, Mosh, and Scheme 9 support the feature, whereas Gauche, MIT, Chicken, Bigloo, Scheme48/scsh, Kawa, SISC, Chibi, STklos, and SSCM don't.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#185 Add sixth "centered" division operator

From the Guile manual:

  • Scheme Procedure: centered/ x y
  • Scheme Procedure: centered-quotient x y
  • Scheme Procedure: centered-remainder x y

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|.

Note that these operators are equivalent to the R6RS operators div0, mod0, and div0-and-mod0.

--Andy Wingo

Taylor Campbell thinks these are useless. We should probably have use cases for _any_ division operator we include.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: no

#195 Editorial: proposed rewording for begin

The documentation for `begin' specifies that it is a sequential construct; but really it splices as well, and also of course it's a keyword for the module system currently. This is inaccurate of the spec to say that "begin is for sequencing".

Suggestion: adopt the language of R6RS section 11.4.7.

--Andy Wingo

We should explain somewhere the four kinds of begins: (begin expr ...), (begin decl ...), top-level begin, and module-top-level begin. Note that R7RS like R5RS does not have (begin decl ... expr ...).

Vote yes to adopt the R6RS description, modified for differences in the language.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#198 Make it an error for a procedure mapped by MAP and friends to mutate the result list/string/vector

This is possibly difficult to enforce, and can break existing R5RS programs written in very bad style.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#199 Make it an error for a procedure mapped by MAP and friends to return more than once

This is possibly difficult to enforce, and can break existing R5RS programs.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#200 Completing the blob procedures

Add blob, blob-map, blob-for-each, and blob conversion functions to and from lists/vectors/strings.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: no

Blob's don't have an internal structure to map or for-each over. Sure, we can measure positions in them in bytes, but that's distinct from saying they're *made* of bytes.

#205 Roll partial-blob-copy(!) into blob-copy(!)

... with extra arguments.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: no

#206 Provide read-syntax for blobs

R6RS provides a #vu8(...) read-syntax for bytevectors. SRFI-4 uses #u8(...).

  • Options: r6rs, srfi-4, none, undecided
  • Default: none
  • Preferences: srfi-4,none,r6rs

#207 Editorial: Polar complex numbers are inexact

Add a note saying that 1@2 and (make-polar 1 2) MAY evaluate to an inexact complex number.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#208 Is || a valid identifier?

The grammar in 7.1.1 allows || as an <identifier>. However, page 5 suggests the |...| form is only for convenience (e.g. |foo bar| is equivalent to foo\x20;bar). There's no way to normalise || to anything without the vertical bars that's a valid identifier. Was that intentional, or should the rule be

<vertical bar> <symbol element>+ <vertical bar>

Vote remove to remove the |...| syntax altogether.

  • Options: remove, empty-valid, empty-invalid, undecided
  • Default: empty-valid
  • Preferences: empty-valid

What else would (string->symbol "") return?

#191 Include CLOSE-PORT ?

Should we include close-port, as a generic version of close-input-port and close-output-port?

  • Options: yes, no, undecided
  • Default: no
  • Preferences: no

#188 Clarify wording of and and or definitions

The definitions of and and or may be slightly confusing. Reword them to be more clear. One possible hiccup is that the current language permits the return of different false values, while a clearer wording may preclude this.

R6RS provides a clearer definition that does not provide wiggle room for multiple false values. Should we use that?

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#187 Clarify duplicate bindings in let*

The language of the standard could clarify that duplicate bindings are permitted in the clauses of a let*.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: yes

#215 initial value argument to make-blob

make-blob should either have an initial value argument, or rationale why it is inconsistent with make-vector and make-string.

Vote yes for an initial value argument.

  • Options: yes, no, undecided
  • Default: no
  • Preferences: no

BLobs don't have an internal structure to "fill". Let new blobs be all zeroes, as there's no boundaries in a string of zero bits...

#216 Controlling use of reader labels on output

There are cases when one does not want to output reader labels for shared structure, such as when you don't care (and want the output to be more legible), or when you know that the time or space requirements to construct the table will be too large.

We could offer a parameter to control this, or have a separate procedure (e.g. write/simple) which doesn't use the reader labels.

Finer grained control may also let use specify a predicate for which values are interesting (e.g. never use labels for strings), or only use labels for cycles, etc.

  • Options: parameter, write/simple, none, undecided
  • Default: none
  • Preferences: write/symbol,none,parameter

Putting too much of this stuff into parameters means it's easy to assume wrongly about how write will behave, forgetting that some caller might tinker with some parameter and BREAK YOU.