Reflecting on the metalevel interpreter written in direct style
This paper presents a reflective Scheme system in which user programs
are allowed to go up to the metalevel interpreter, access to it, and
even modify (parts of) it.
Since the metalevel interpreter defines the operational semantics of
the baselevel program, the system effectively allows users to modify
the semantics of the language.
The novel characteristic of the system is that the metalevel
interpreter is written in direct style.
Conventionally, the metalevel interpreter of a system with a
(behavioral) reflective facility has typically been written in
continuation passing style (CPS) to make the control structure
In our system, the same information is obtained via delimited
continuation constructs: shift and reset, a variant of call/cc.
With the help of shift and reset, the metalevel interpreter becomes
simpler and easy to understand without sacrificing the reflective