R7RS Tasks

General structure

The r7rs egg has been implemented and provides basic support for R7RS features not already implemented in the core system. There are still a number of incompatibilities and some missing functionality.

Open is also whether more features should move to the core system or whether support of the language as an egg provides integration enough to not annoy users who simply want to code in R7RS with minimal effort.

The remaining document tries to reflect the current status of R7RS Scheme support on CHICKEN.

comments by John Cowan marked with JC:

Todo

Outstanding tasks:

\x escapes in |...|
#\x...; character syntax
export renaming
eqv? corner cases (probably not, see below)
equal? must not diverge
with-exception-handler thread safety
Feature identifiers as in Appendix B (see below)

Nice to haves:

(srfi 1) and (srfi 13) reexport optimizations
.inline files
.types specializations
#!fold-case support without (import (scheme read))

The egg also needs a more comprehensive test suite.

Classification of changes

(+): Trivial or straightforward changes
(*): Changes that are difficult or work-intensive
(X): Changes that break backwards-compatibility
(?): Needs to be clarified

Currently unimplemented changes

2.1. Identifiers

|...| needs support for \x...; escape syntax, which is not fully compatible to the existing \xXX format. A backwards-compatible change should be possible but will have ambiguous cases like |\x12;|. (X)

6.7. Strings

\x...; syntax. The same issues as in |...| identifier names. (X)

Appendix B

Without a canonical list of features and their exact meaning this is mostly useless.
- JC: The ones that CHICKEN should provide (as symbols, not as keywords) are: (+)
  - r7rs
  - ieee-float
  - exact-closed, exact-complex, ratios (not in CHICKEN 4 unless the numbers-egg is loaded, perhaps not even then),
  - full-unicode
  - the values of (machine-byte-order), (machine-type), (software-type) (with posix instead of unix), and (software-version)
- FW: This should be implemented in the core system (+)

5.6.1. Library syntax

The export declaration will require renaming, which is currently not available in the module system. Requires a bit of work. (*)
(include "filename") takes filename to be relative to the current directory. Other R7RS implementations interpret filename relative to the file containing the include.

6.1. Equivalence predicates

eqv? may have some corner cases for funny IEEE values (nan, etc.). (?)
- JC: Not that I can see: (eqv +nan.0 +nan.0) can return either #t or #f in R7RS.
equal? must handle circular data. Change this in core? Probably, since this needs to be fast. Applies to equal=? as well.

6.11. Exceptions

with-exception-handler. I think this is not compatible to the current version. (? *)
Clarify exact semantics of raise. (? *)
- JC: Same as Chicken's abort.
Implementing guard correctly will need some thought, due to the wild jumping between dynamic environments. (*)
- JC: It's actually very close to Chicken's handle-exception.

List of R7RS features that are provided by the r7rs egg

2.1. Identifiers

#!fold-case, #!no-fold-case.

4.1.7. Inclusion

Multi-argument include, include-ci.

4.2.1. Conditionals

cond-expand support for library.

4.3.2. Pattern language (syntax-rules)

"Underscores also match arbitrary input elements but are not pattern variables ..."
(<ellipsis> <template>). This is currently not available, IIRC.

5.2. Import declarations

import. A library name may not begin with a modifier-keyword like only.

5.5. Record-type definitions

define-record-type, generative.

6.3. Booleans

#true, #false

6.4. Pairs and lists

make-list. See SRFI-1.
3-argument member and assoc. See SRFI-1.

6.6. Characters

char-foldcase currently only supports ASCII
Extend char=?, char<? et al. to accept arbitrarily many arguments

6.7. Strings

Extend string=?, string<? et al. to accept arbitrarily many arguments.

6.7. Strings

string->list with start/end arguments.
string-copy, string-copy! and string-fill! with start/end arguments. See SRFI-13.

6.8. Vectors

vector->list, list->vector and string->vector with start/end arguments. Provide specializations.
vector-copy! and vector-fill! with start/end arguments.

6.10. Control features

string-map and string-for-each are not compatible with SRFI-13 version.

6.12. Environments and evaluation

environment.

6.13.1. Ports

get-output-string.

6.13.3. Output

write-string with start/end arguments.
write. Support for labels and circle-detection.

6.14. System interface

2-argument load.
exit with boolean arguments.