brainstorms

Thursday June 22, 2006

r6rs syntax-case macros

scheme continues to improve on the only worthwhile syntax extension mechanism (macros) ever devised for any programming language. the srfi-93 [just issued] is a description of the draft r6rs syntactic abstraction system from the current scheme standardization process.

the hygiene condition:

A binding for an identifier introduced into the output of a transformer call from the expander must capture only references to the identifier introduced into the output of the same transformer call. A reference to an identifier introduced into the output of a transformer refers to the closest enclosing binding for the introduced identifier or, if it appears outside of any enclosing binding for the introduced identifier, the closest enclosing lexical binding where the identifier appears (within a syntax template) inside the transformer body or one of the helpers it calls.