Library system in Stak Scheme

@raviqqe

February 18, 2024

Contents

• Stak Scheme
• Library 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.

Library system in R7RS

Defining a library

• Libraries export symbols.
• Libraries import symbols from other libraries.
• Libraries are "called" but only once.

(define-library (foo)
  (export foo)

  (import (scheme base))

  (begin
    (define (foo x)
      (write-u8 x))))

Library system in R7RS

Importing a library at a top level

(import (foo))

(foo 65)

Where to put libraries?

• Where to put libraries?
  • Inlining library clauses (e.g. Gauche)
  • Libraries as files (e.g. Chibi Scheme)
• Stak Scheme took the inlining solution.

(define-library (foo)
  (export foo)

  (import (scheme base))

  (begin
    (define (foo x)
      (write-u8 x))))

(import (foo))

(foo 65)

Implementation in a compiler

Pipelines

1. Read source.
2. Expand libraries. <- new!
   • Read all (define-library ...) clauses.
   • Expand all (import ...) clauses.
3. Expand macros.
4. Compile expressions.
5. Encode objects.
6. Write bytecodes.

Library expansion

• Environments of libraries are separated by symbol prefixes.
  • e.g. foo -> $42$foo where 42 is the ID of a library
• Importing symbols from a library converts all symbols' prefixes.
• Top-level symbols do not have any prefix.

Future work

• Library system
  • (rename ...)
  • (prefix ...)
• eval procedure

Summary

• Building a library system is fun!