Re: Compiling expressions

James Harris <james.harris.1@gmail.com> 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.


An interesting requirement.


I can understand need for speed, size, and such, and maybe one
of those requires a hand-written (hand optimized) parser.


If you are so restricted, do you allow your parser to be written
in a high-level language? To be compiled by a non-handwritten
compiler?


> 2. Efficient and without backtracking.


Seems reasonable to me, though the languages has to allow for it.


> 3. Precedences (and possibly associativities) defined in tables.


Tables most easily generated automatically, by a parser generator?


> 4. Output to be a tree structure.


> 5. Parenthesised subexpressions allowed.


> 6. Some operator families are *not* to associate with each other.
> See below.


So you generate an error when such occurs. The usual problem is
to make the error message good enough that one can figure out
what happened.


> 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).


> Infix and postfix operators use distinct symbols. For example, if a
> certain symbol were used as a postfix operator it could not also be
> used as an infix operator.


(snip)


-- glen

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