REPL Semantics of Chez Scheme

Introduction

Chez Scheme represents an example of a high-speed incremental compiler with an interactive environemnt that follows a traditional lisp REPL behavior. It is interesting to note that Chez Scheme achieves high performance while still providing a dynamic environment, though the optimizations that Chez Scheme can make are limited by the top level semantics.

Official Documentation

The Chez Scheme User's Guide Version 8 provides a chapter on the Interaction Environment of Chez Scheme. The reader is referred to this reading for the full description.

Important Key REPL Semantics

• Expressions are entered at the REPL one at a time
• Each expression received is expanded and evaluated in the current interaction environment before the next expression that is entered is processed
• Files that are loaded by reading each form in the file and processing each in turn, as if they had been entered by hand into the REPL
• There is a single interaction environment containing bindings to macro transformers and procedures
• The initial environment is the Chez Scheme default environment
• All initial bindings are immutable
• Definitions are mutable
• Initial bindings may be redefined
• A parameter exists that allows you to alter the interaction environment using environment controls
• All identifiers are considered implicitly bound if not already defined
  • This allows recursive definitions to be entered one at a time
  • As a result, top-level identifiers will mess with free-identifier=?, requiring auxilary syntaxes to be explicitly bound instead of implicitly used
• Top level identifiers are not optimized away, since they may be reassigned