Implementing R7RS on an R6RS Scheme system

The Scheme language has three major standards; Revised Report on the Algorithmic language Scheme (R5RS) standardised in February 1998, the Revised Report on Algorithmic language Scheme (R6RS) standardised in September 2007 and the Revised Report on the Algorithmic language Scheme (R7RS) standardised in July 2013. R7RS, the latest standard of Scheme focuses on the R5RS compatibility thus making R5RS implementations compliant with it would not be so difficult. For R6RS implementations it would be much more difficult; R7RS clearly says it is not a successor of the R6RS. This paper describes the major differences between these two Scheme standards and how we made our Scheme system, Sagittarius, compliant with both R6RS and R7RS, and made it able to use both standards’ libraries seamlessly.