Chicken Scheme 6.0: Release Overview

The 6.0.0 update marks a significant milestone, primarily by integrating all modules defined by the R7RS small language directly into the core system.

🌐 String & Character Enhancements

The internal architecture for strings has been overhauled to use UTF-8, ensuring full $\text{UNICODE}$ compatibility.

• Indexing: Locatives on strings are now based on code-points rather than raw bytes.
• Character Management: The char-name procedure now supports the removal of named character definitions.
• Escaping:
  • symbol-escape now toggles whether symbols are displayed in escaped mode (|...|).
  • Symbol printing logic is now more rigorous regarding when escaping is required.
  • Hexadecimal escape sequences now strictly require a terminating ; character, adhering to R7RS standards.

📦 Data Handling & I/O

Bytevectors and Blobs

The system has transitioned from (chicken blob) to (chicken bytevector), which provides R7RS-compliant operations.

Port & File Operations

• Encodings: open-input-file and open-output-file now support encoding arguments (Default: UTF-8; also supports Latin-1).
• Port Creation: make-input-port and make-output-port now utilize keyword arguments for optional methods.
• New Ports: Added make-binary-input-port and make-binary-output-port.
• Port Naming: set-port-name! has been deleted; please use the SRFI-17 setter for port-name.
• File Locking: The (chicken file posix) module now employs the flock(2) system call, which is thread-safe and operates on entire files.

🏗️ Module Architecture & Migration

Many primitives have been relocated to align with R7RS.

Detailed Relocations

• To (scheme base): exact-integer?, exact-integer-sqrt?, vector-copy!, make-parameter, call/cc, open-input-string, open-output-string, get-output-string, input-port-open?, output-port-open?, parameterize, and port?.
• To (scheme case-lambda): case-lambda.
• To (scheme base) (with signature change): write-string (moved from (chicken io)).
• Generative Records: define-record-type is now generative and resides in (scheme base). Consequently, record-instance? and make-record-instance now accept non-symbolic type specifiers.

Deprecations & Renaming

• Remove srfi-0, srfi-6, srfi-9, srfi-11, srfi-23, srfi-39, and srfi-98 (absorbed by R7RS).
• Rename r4rs, r5rs, r4rs-null, and r5rs-null to (scheme XXX).
• Rename platform identifier mingw32 to mingw.

🔢 Numerical & Mathematical Updates

Number Vectors

A new module, (chicken number-vector), provides a superset of SRFI-4, adding support for 64-bit and 128-bit complex number vectors. The original srfi-4 module remains but is restricted to the SRFI-4 specification.

Complex Numbers & Arithmetic

Using LaTeX notation, the following logic now applies:

• Rectangulars: make-rectangular returns a complex number if the imaginary part is an inexact $0$.
• Imaginary Parts: imag-part returns an exact $0$ when the input is not a complex number.
• Parsing: string->number and the reader now correctly process complex numbers where the imaginary part is a negative inexact $0$ (e.g., $a + (-0.0i)$).
• Comparison: max and min will ignore NaN values provided a non-NaN argument is present.

Base Conversion

number->string now supports bases up to $36$ (previously $16$). string->number has been improved to handle the character "i" more consistently in bases $> 18$.

⚙️ Syntax & Compiler

Expansion & Macros

• Single Expansion: Added expand1 to (chicken syntax) and the ,x1 command to csi for expanding macros exactly once.
• Tail Patterns: syntax-rules now offers improved support for tail patterns involving ellipses.
• Includes: include and include-relative now accept multiple files; include-ci is newly available.
• Library Specs: define-library now supports export-all.

Read Syntax

The #ci'/#cs'` syntaxes are gone. Use the following instead:

#!fold-case
#!no-fold-case

🔌 Foreign Function Interface (FFI)

The FFI has been optimized for performance and flexibility:

1. Direct Passing: Strings and symbols are no longer copied when passed to foreign code. Warning: Mutations made by external C code will be reflected in Scheme.
2. Direct Types: C structs, unions, and complex numbers can now be passed as arguments and returned as results directly.

🛠️ Tooling & Installation

Compiler & Interpreter

• The flag -r5rs-syntax is now -r7rs-syntax and no longer disables extended symbol syntax.
• Paths: Library procedures and make-pathname now consistently use forward slashes (/).
• File System: delete-file and delete-file* now behave identically when encountering broken symlinks.

CSI & Debugging

• The "feathers" debugger is no longer part of the core; it is now an egg.
• set-describer! has been removed from the csi module.

Installation & Config

chicken-install now implements locking for the cache directory. In egg specifications, csc-options and link-options now support custom-config forms.

Important Note on Tool Arguments: Tool paths containing spaces are now handled without requiring double-quotes. However, as a result, the system no longer accepts space-separated flags for tool arguments.

If you require specific flags, please wrap the tool call in a short shell script.

Miscellaneous

• load and load-relative now allow the second optional parameter to be either an evaluation procedure or an environment.
• Added number-vector-data to the (chicken memory representation) module.