LL1
It’s been a while since I’ve posted something directly programming-related, so here goes. The mailing list that resulted fom the Lightweight Language Workshops at MIT is a gold mine, and something I keep coming back to read.
A lot of the most interesting and fundamental questions in programming language design tend to be debated in echo chambers: programming communities seem naturally insular in the way that any linguistic community is. While the best hackers in any language will of course frequently debate others within their community, it’s pretty rare that interesting discussion happens across language boundaries. The LL1 list was an exception, and featured a bunch of top-notch programmers (Guy Steele, Paul Graham, Avi Bryant, Robby Findler, Shiram Krishnamurthi, Matthias Felleisen, Joe Marshall, Dan Weinreb, Olin Shivers, Scott McKay…). The ensuing traffic covers all of the interesting topics: syntax, macros, environments, typing, language design, functional programming, etc.
Some highlights:
- The Scheme mistakes thread.
- Guy Steele’s Scheme interpreter that’s sufficiently complete that it can run Kent Pitman’s “evil code”.
- An interesting discussion of the power of macros, including neat examples of their power from Steele and Noel Welsh, and rebuttal by Trevor Blackwell of most of the arguments put forward. (That nobody could come up with a powerful example of a use of macros that can’t be easily implemented in a language that lacks them is surprising, to me at least.)
- Steele: “Only later, after our discovery that actors and closures of lambda expressions were implemented by identical mechanisms did we consider extending Scheme to become a useful programming language.”
- Good discussion of file-oriented and image-oriented environments. (Scott McKay was a founder of Symbolics, and Avi Bryant is a well-known Squeak/Smalltalk hacker—Symbolics’s Genera and Squeak are still two of the most impressive programming environments ever created.)
- Questions for a language designer.
- The origin of the “HREF Considered Harmful” phrase, which (by analogy) expresses perfectly the advantage of continuation-based web frameworks. (Someone notices early on how this doesn’t immediately mix well with what-we-now-call AJAX.)
- “I don’t think I intentionally misled Yahoo (too much) on this point, but if I did it was for their own good.”—Paul Graham, on pitching obscure languages to big companies.
- Static typing: “It is merely a tradition.” “[There are] TWO different traditions.” “It is the fact that a quantity may have connections to many places in a program text that makes it valuable to document the expected invariant properties of that quantity; type is one useful kind of invariant.”
- OO flamewars.
- Steele’s candidate for the worst computer science pun in the history of the field: “It seems [functional programmers] believe in the separation of Church and state”.