Some aspects of Basel, the base language for an extensible language facility
Philippe Jorrand · ACM SIGPLAN Notices · 1969
Basel has been designed as the base language component for an extensible language facility called Elf. Elf will have several components: one for syntactic extension, one for the definition of communications with a given kind of environment, and some others. All these components will be able to perform modifications, additions, and deletions to Basel.