On 12/12/2010 04:09 PM, John Cowan wrote: > Working Group 2 has decided that an optional pattern matching module > will be part of R7RS.
To "win" pattern-matching really should be the default and integrated into the language core, rather than an optional module that uses separate keywords. E.g. there shouldn't be a difference between lambda and match-lambda*. The latter is too verbose! For example R6RS defines lambda as: (lambda <formals> <body>) Could we change it to: (lambda <pattern> <body>) where <pattern> could be based on <pat> in match.ss: http://download.plt-scheme.org/doc/372/html/mzlib/mzlib-Z-H-27.html#node_chap_27 True, there will be be some complications and incompatibilities, with R6RS and possibly with implementations that don't support patterns. At the least we could have a standard library that redefines the standard keywords lambda, let, ... etc to versions that support patterns. The biggest issue appears to be define. Changing define to have the syntax: (define <pattern> <expression>) conflicts with: (define (<function> <formals>) <body>) I don't see a safe way to generalize define to handle patterns in way that existing code will work. So I think we need a new keyword - but I'm hoping for something shorter than match.ss's match-define - preferably something even shorter than define. Perhaps one of: (def <pattern> <expression>) (::= <pattern> <expression>) Related: The traditional let makes for a lot of parentheses, which perhaps contributes to the Scheme-turn-off. Perhaps instead of: (let* ((var1 exp1) (var2 exp2) (varn expn)) bexp1 bexpn) perhaps the above should be discouraged and this style be recommended instead: (begin (def var1 exp1) ;; OR: (::= var1 exp1) etc (def var2 exp2) (def varn expn) bexp1 bexpn) Even more valuable than improved readability is that it makes the code more robust to changes: You can add, remove, and move variable definitions without having to add/remove let-blocks and changing indentation levels. -- --Per Bothner p...@bothner.com http://per.bothner.com/ _______________________________________________ r6rs-discuss mailing list r6rs-discuss@lists.r6rs.org http://lists.r6rs.org/cgi-bin/mailman/listinfo/r6rs-discuss
