Re: Articles/books that discuss separating the context-free part of a language from the context-sensitive part?

"Costello, Roger L." <costello@mitre.org> writes:
>The poster makes the point that most programming languages define a
>context-free core, and then have additional algorithms which run on the parse
>tree to filter out constructs that are illegal in the language:
...
>[ [...] it also permits much better
>error messages. -John]


That depends on the syntax of the language. E.g., at one time
Modula-2 was the language used in our introductory programming course
25 years ago, our students used to write things like


a<3 AND b<3


and the compiler reported a type error (a and b were of type INTEGER).
But it really was a syntax error. The students should have written


(a<3) AND (b<3)


because the implicit binding was


a<(3 AND b)<3


and "3 AND b" was a type error. This error message confused the
students no end.


- anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/

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