File system in Stak Scheme

@raviqqe

June 23, 2024

Contents

• Stak Scheme
• File system in R7RS
• Implementation
• Future work

Stak Scheme

• A bytecode compiler and virtual machine (VM) for Scheme
• The compiler is written in Scheme.
• The VM is written in Rust.
• It aims to support R7RS-small.

File system in R7RS

Generic I/O

• Port type
  • input-port?, output-port?
  • call-with-port
• Read operations
  • read-u8, read-string, read
• Write operations
  • write-u8, write-string, write
• close-port

File system in R7RS

File operations

• open-input-file
• open-output-file
• delete-file
• file-exists?

Implementation

Generic I/O

• A port type
• vtable-ish implementation

(define-record-type port
  (make-port read write close)
  port?
  (read port-read)
  (write port-write)
  (close port-close))

Implementation

• Primitive file operations talks to libc directly.
• Rust's std crate doesn't expose some underlying details.
  • e.g. file descriptors

Opening files

(define (open-file path output)
  (let ((descriptor ($$open-file (string->path path) output)))
    (unless descriptor
      (error "cannot open file"))
    (make-port
      (lambda () ($$read-file descriptor))
      (lambda (byte) ($$write-file descriptor byte))
      (lambda () ($$close-file descriptor)))))

Future work

• More R7RS compatibility
• Efficient Scheme file compilation in Rust projects