I'm defining an intermediate language for a multi-backend code generator that I'm writing.  I want to document the operational semantics for this intermediate language in a way that is readable both from within the source code and generated documentation (ocamldoc).  The notation introduced used in Types and Programming languages is great for a book, but I don't want to try to do the prerequisite over conclusion style notation via ASCII art.Is there a widely recognized notation for operational semantics that doesn't require non-ASCII characters?  I looked through various RFCs but can't find any that use a non-natural language way of specifying semantics.
Notation for operational semantics that can be used in code comments
programming languages;semantics;operational semantics
The input format for the tool OTT is based on ASCII and the rules look very much like type system/operational semantics rules. Maybe you could use that format. I'm sure that the parser for the input format is available as open source.