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CHICKEN 6 roadmap

Here's a proposed list of things we would like to see in CHICKEN 6. Feel free to add more details if you know of a way to implement something or have an idea how to improve some part. Please, no editing flamewars here!

Full Unicode support [implemented]

As described in UNICODE transition full support for extended character sets will be added. This includes several API changes, a bytevector module and a few incompatibilites that are deemed necessary for a clean integration.

These changes to the runtime system have been implemented and undergo testing. Due to the nature of the changed internal string representation and differences that are caused by the stronger distinction between textual strings and other byte sequences, a number of incompatibilities to CHICKEN 5 will have to be taken into account, which, in my opinion, are necessary and can not be prevented.

R7RS support [implemented]

The r7rs egg has been integrated into the core system. All (scheme ...) modules specified by R7RS are available for user code. For easing the porting of existing code, the scheme module still refers to R5RS Scheme and is an alias for R7RS' (scheme r5rs) library module. Toplevel code outside of any module still defaults to R5RS, just enter

 (import (scheme base))

to have an R7RS-compliant environment.

Several incompatibilities to CHICKEN 5 exist and are listed here:

• Module (chicken base): symbol-ecape has been removed; exact-integer-sqrt?, vector-copy!, make-parameter, call/cc, open-input-string, open-output-string, get-output-string, input-port-open?, output-port-open? and port? have moved to (scheme base), the same applies to parameterize; case-lambda moved to (scheme case-lambda).
• Module (chicken platform): features moved to (scheme base) and returns a list of symbols, not keywords.
• Module (chicken file posix): file-read requires a byte-vector argument.
• Module (chicken random): set-pseudo-random-seed! and random-bytes require a byte-vector argument.
• Module (chicken io): write-string moved to (scheme base), the meaning of its arguments has been changed to conform to R7RS.
• define-record-type (now part of (scheme base)) is generative - each definition creates a new type; this results in that a record type may be a non-symbol (currently a one-element vector is used), making record-instance? and make-record-instance less strict about the record type argument; record-printing assumes symbols or vectors are used as record type.
• The second (optional) parameter for load and load-relative may be either an environment or an evaluation procedure.
• The module aliases srfi-0, srfi-6, srfi-9, srfi-11, srfi-23, srfi-39 and srfi-98 have been removed (all of these are covered by R7RS).
• The modules r4rs, r5rs, r4rs-null and r5rs-null have been renamed to (scheme XXX).
• Hexadecimal escape sequences in strings and extended symbols must be terminated by the ";" character, following R7RS.
• The compiler and interpreter option -r5rs-syntax has been renamed to -r7rs-syntax and does not disable extended symbol syntax (|...|) anymore.
• The #ci/#cs read syntaxes have been removed, use #![no-]fold-case markers instead.
• include and include-relative accept multiple filenames, include-ci has been added.
• The "blob" module has been removed and replaced by the chicken.bytevector module, which is mostly mapped into (scheme base).
• Strings and symbols passed to foreign code are not copied, they are passed directly, any mutations done by external code will be visible on the Scheme side.
• SRFI-4 "blob" conversions have been renamed, a shim egg will be provided that contains all the functionality using the old names, but needs to be imported in a separate step.
• String-locatives index by character position, not byte-position; size changes due to destructive string-mutation are not detected or handled.
• "blob" read-syntax (#${...}) has been removed, R7RS #u8... can be used instead.
• Module srfi-4: read-u8vector, read-u8vector! and write-u8vector have been removed, use the new bytevector I/O operations from (chicken io) instead or what (scheme base) provides.
• Module (chicken port): Removed set-port-name!, use SRFI-17 setter instead, make-input-port and make-output-port take additional port methods as keyword arguments.

The manual is likely to need a lot of clean ups and corrections.

C code cleanups

A number of historical C preprocessor definitions are used throughout the runtime system that have no use anymore, most notable C_TLS, C_externimport, C_externexport and C_fcall. These should be removed.

Remove the "Feathers" debugger from the core system

I (felix) would like to move this into an egg. It doesn't seem to be used a lot and has a number of shortcomings which I currently don't have the capacity to address. Moving it into an egg separates the maintenance and makes it easier to modify or replace.

Windows support

A recurring question. We have little resources and keeping the support for various toolchains is a challenge and adds a lot of complexity. Possible approaches would be to concentrate on a single toolchain or simply require WSL2 and drop special support completely.

--- Chicken is one of the few Schemes that can deliver a standalone (static) or nearly standalone (executable + DLLs) programs, and that is an important capability. Users are used to copying EXE files or unzipping archives or (especially) running installers. Asking them to install WSL2 *as an execution environment* is too big an ask. That said, I think it would be fine to abandon all toolchains except mingw64. Of course, MSVC would be even better, but obvs we don't have that capability. (jcowan)

(Note that Cygwin support can stay, as the differences are not too big.)

Current status

The UTF- and R7RS support has been mostly implemented and is available in the git branch utf+r7rs. To build the system from scratch, there are currently two bootstrapping steps involved (sorry):

• Checkout utf-bootstrap and run make boot-chicken.
• Checkout utf+r7rs and run make CHICKEN=<path-to-chicken-boot-built-previously> ... and then make CHICKEN=./chicken boot-chicken (I'm not sure whether the former build step is needed, but just in case...)
• Checkout utf+r7rs and build it using make CHICKEN=<path-to-chicken-boot-built-last> ....

The reason this is currently so involved is that there are two internal changes that influence the generated code: the internal string representation (for UTF) and the changes to what modules export which identifiers. These changes require to build chicken compilers with successively added extensions and modifications, otherwise you will end up with an unbuildable system.