eval in Stak Scheme

@raviqqe

May 12, 2024

Contents

• Stak Scheme
• eval in R7RS
• Implementation in Stak Scheme
• 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.

Progress

• The eval procedure
  • Only procedures available
  • No macro support yet
• The stak-profile command
  • Traces and profiles Stak Scheme codes.

eval in R7RS

• The eval procedure evaluates an S-expression.
• Only global bindings in a given environment are accessible.

(eval <expr-or-def> <environment>)

Example

(import (scheme base) (scheme eval))

(eval
  '(display "Hello, world!")
  (environment '(scheme write)))

Environments in R7RS

• (environment <specifier> ...)
  • Imports immutable environments of specifiers.
  • Normal libraries (e.g. (scheme base) and (scheme write)) can be used for the specifiers.
• (interactive-environment)
  • A mutable environment for REPL

Implementation in Stak Scheme

• The compiler injects library and macro information built in a compiler into target codes.
  • ($$libraries) and ($$macros) primitives
• Keeps portability of the compiler.
  • The other Scheme implementation can be used to run the compiler.
• Duplicates codes related to compilation and macro expansion in a (scheme eval) library.

Demo

Future work

• Macros in eval
• Deduplication of codes between a compiler and the (scheme eval) library

Summary

• Building eval is fun!