Re: Why context-free?

Neelakantan Krishnaswami <neelk@cs.cmu.edu> wrote:
>Splitting the task of parsing into phases -- a) lexing, b) parsing,
>and c) type-checking -- is just plain old good engineering...


This can apply even to things that are not traditionally thought of as
languages. The second or third time I implemented POSIX regular
expressions, I experimented with using a distinct scanner and parser
rather than trying to do everything in a parser. I was startled at how
much easier this was, and how much cleaner the code was. All sorts of
things that had previously contorted the parser logic became two lines of
code apiece in the scanner. In particular, the distinction between
"basic" (ed-style) and "extended" (egrep-style) REs became essentially
a choice of two different scanners, invisible to the parser.
--
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mail to henry at zoo.utoronto.ca instead. | henry@spsystems.net

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