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Article contents:[[toc:]] == R7RS Tasks === General structure The [[/eggref/5/r7rs|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 [[/eggref/5/r7rs|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. Description of your changes:

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