Re: Compiling expressions

On Sat, 29 Dec 2012 05:11:16 -0800 (PST), James Harris wrote:


> Compiling expressions is turning out to be more 'interesting' than I
> anticipated! My requirements I believe to be fairly generic but they
> seem not to be supported by standard algorithms so it's not as simple
> as it might be. I thought I would post here as much out of interest as
> anything. I'm not after a prebuilt solution but would be interested to
> hear from other folks who have had similar issues to address. The
> requirements are:
>
> 1. Hand-written, not the output of a parser generator.
> 2. Efficient and without backtracking.
> 3. Precedences (and possibly associativities) defined in tables.
> 4. Output to be a tree structure.
> 5. Parenthesised subexpressions allowed.
> 6. Some operator families are *not* to associate with each other. See
> below.
> 7. Monadic prefix, dyadic infix and monadic postfix operators are all
> allowed.
> 8. Prefix and infix operators can use some same symbols (e.g. minus
> sign).


Here is an implementation with an explanation of the technique used:


http://www.dmitry-kazakov.de/ada/components.htm#Parsers_etc


I extended the method, which fairly old, towards non-associativity (#6),
advanced parenthesis (#5, keyed parameter associations), and split
association priorities into left-right pairs. But basically it is still the
same twin-stack method. Everything is table-driven, of course.


--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

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