I guess that extensible syntax is great for language experiments, but I'd be concerned about it becoming a common feature of production programming. I have found that even the simple facility of user-defined operators (not including the `name` form) leads to code that is far harder to pick up and understand. I hypothesize (based on my own experience) that when picking up some new code, a programmer relies to a considerable extent on the mnemonic significance of the names used in the code. Non-mnemonic elements of the code must be learned and committed to memory before they can be read with any facility. This suggests that user-defined syntax (and operators) run the risk of making the task of understanding a new program more akin to learning a new programing language. #g -- At 17:49 15/05/04 +0200, Per Larsson wrote:
I have recently made a small detour into ocaml programming and I'm rather impressed with the generic preprocessor 'camlp4' for ocaml. Camlp4 allows the programmer to (i) interact with the ocaml parser and lexer to extend the concrete grammar with new syntax and (ii) to directly define the translation of such new syntax forms in terms of ocaml abstract syntax. Haskell programmers (at least in GHC) can also manipulate abstract syntax with the Template Haskell extension and the Language.Haskell.THSyntax library, but to my knowing there is no haskell compiler which supports the inclusion of new syntax forms. Wouldn't such a tool be cool? In the haskell community there are a number of handmade preprocesserors (DrIFT, Generic Haskell, HaRP, ...) which are both cumbersome to write, because the authors must write a (partial) haskell parser for every small extension, but also cumbersome to use because of increasing complexity to your makefiles and different standards for error reporting. Also, experimental extensions could quickly be written and evaluated by the haskell users, decreasing the dependency on the compiler maintainers.
Per Larsson
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