Re: Matheval (was: Dos32Lib, Win32Lib)
On 2000-06-01 EUPHORIA at LISTSERV.MUOHIO.EDU said:
EU>> To the author of Matheval ,
EU>> You may of encountered a file I posted somewhile ago
EU>> called parr1.txt, detailing one approach to constructing a
EU>>parser. This has a fair few advantages over other ways of
EU>>evaluating equations or expressions. One of the disadvantages
EU>>is the necessity of making at least two disk accesses , the
EU>parser of d.cuny circumvents this ; however
EU>> as you discovered in one implementation of eval.e ; there were
EU>difficulties. Are you looking
EU>> towards an alternative or merging of these two approaches ,
EU>this is something I was considering > for awhile and mentioned to
EU>d.cuny. He was reticent about that approach.
EU>> This doesn't mean that there's no other way of constructing a
EU>workable parser with
EU>> at least some of the attributes desired , i.e minimal use of
EU>>the disk, ease of configuration ; rapidity of evaluation.
EU>I did take a look at your file, and that's a very interesting
EU>approach, but I don't think it's really suited to what I was
EU>looking to do.
This was really a second option for me to , I had originally just been
thinking in terms of calculator type functionality , as i still do,
then I thought , 'what if i use some more of the resources available
through the o/s' ; dos in this instance , and let the interpreter ;
ex.exe do all the work.
This approach isn't unique to euphoria , any interpreter that provides
system() calls and error checking ; through a file like ex.err might
conceivably be used.
Redirection , through dos , might further improve upon this concept.
eu>First, my goal was to allow 'normal' mathematical
EU>notation, as far as possible to be used exclusively, rather than
EU>hard coding the math into a Euphoria program. I'd say that the
EU>version on the contributions page is a rough draft.
By 'normal' are you referring to document style notation as is found
in professional style math packages , some of these give you the ability
to enter programming code too ; though usually C/C++ code.
In some ways the math is 'hard coded' into euphoria . The include file
that contains the expression being evaluated can be exported or edited
quite readily , through the use of a standard text editor.
Modules might be added , dynamically , to the basic configuration to
perform certain tasks ; like statistics.
What is generated , is a syntax corrected sequence , suitable for use
within euphoria ; further evaluation might then occur using something
like the evaluator that you had in the rough draft. Though this appears
to be a little slow for some applications. This sequence might be
amenable to symbolic manipulation.
The rough draft was what I found myself evaluating , I'd like to see
something that is without the hiccups , perhaps in shrouded form ; if
you wish to protect your code.
EU>There are several quirks about the parser and naming conventions
EU>(eg, can't have a var begin with the same characters as an existing
EU>function), but it seems to work fast enough. You would only need
EU>to parse an expression once, and then you'd have the expression in
EU>matheval format, able to pass it directly to the evaluation
EU>routines.
Are right brackets automatically appended now , or are these seen
as being unnecessary clutter.
I'm a little unfamiliar with recursion , hence my tendency to bury my
head in the sand , a bit more familarity might put me at ease with
this approach.
EU>I really haven't worked on the parser lately, since it works. I've
EU>been focusing on the meat of the code, and I've been putting off
EU>fixing the other 'inconveniences' for later. I think that it is
EU>fairly easy to reconfigure. To add a function to the parsing, you
EU>basically need to add it to the list of functions, insert it
EU>wherever it needs to go withing the precedence table, and write the
EU>code to 'collapse the token' (as I put it). These tend to be no
EU>more than 5 or 6 lines of code, most of which is simply concerned
EU>with the number of arguments required for the function.
F(x1,x2,x3,....,xn) = type functions are readily available with my
approach , is this true of yours also ?
If you can also evaluate these and with only a few more lines of code
I'm definitely interested in reviewing your approach.
By collapsing the token I assume you mean making a corresponding
sequence , to the equation , that can be more quickly evaluated ; within
a loop ; perhaps even an assembly language loop. To date I haven't
bothered with this possibility as once the function has been defined ,
within the editable include file I can generate an output sequence of
values from an input sequence of values in the usual manner with just
a few lines of euphoria code.
EU>In the development of the parser, I'd looked at David Cuny's (and a
EU>couple of others' libs that were posted), but they didn't seem to
EU>have the right sort of functionality that I needed, so the parsing
EU>routines are pretty much all mine.
Hence , understandably , your reluctance to be overly public with your
code. These are my feelings also , hence my posting parr1.txt that tells
you how to ; without giving any detail. With the type of convoluted code
you might be involved with I'd be even more reluctant to post. Parsers ,
especially small functional ones can appear to be real mind benders.
Some of the literature surrounding these , as you're probably aware ,
is pretty daunting until you break through some unknown barrier of
comprehension. To some extent I managed this , though not at the basic
level of understanding I'd prefer.
EU>One reason I don't want to hard code anything is that I'm
EU>interested in being able to manipulate the expressions
EU>symbolically--factor, integrate, diferentiate, trig identities, etc.
EU>I can't see how you would be able to do that using your model,
EU>since you're not really parsing the expression, but equivalent
EU>Euphoria code.
The sequence that contains the, syntax corrected , expression
might be manipulated symbolically , I haven't really looked into this , as
potentially , this involves more complexity than attempting to parse the
sequence using the basic concepts. There might be a way to circumvent this,
note that Euphoria [ or any other ] interpreter tends to minimize the
components of an expression and tests for a certain amount of equivalence.
Anyway , I should get some text , if I don't have an unexpected brainwave
first .
hint:
Associative sequences.
EU>I don't think that you've ever mentioned what your application was.
EU>I'd be interested to see it if you've made progress.
I posted the concept in parr1.txt , after I'd written software that
worked ; rather than the other way around.
I tend to have some difficulty with my DOS based browser , hence the
software doesn't appear on any of the euphoria contribution sites .
As this type of software might not exist , except for the features
available through euphoria , I don't mind discussing this at all ,
probably I should make all of the code available . A bit of scrutiny
from more competent software developers, than I, might lead off into
new directions.
I suppose I could send , in plain text format , the code to this list
server ; I think it's about 120k . I shall do this only if requested.
The software that exists , presently , evaluates an expression of
the form f(x) = sin(x*pi) + sinh(x) , or similar , where -1 <= x <= 1;
then graphs the resultant (x,y) values in 800x600, 256 color resolution.
An error message is generated , if your equation/expression has a fault
with the syntax. This is also a rough draft , some expressions can't
be graphed because f(x) returns an undefined value ; these exceptions
can be handled through software in a general way or at the level of
the basic functions,I just haven't written this code yet.
I wanted reliable software that was , small in size , my own , that
I might send to others ; that evaluated large expressions , graphed
these and perhaps did things like integration.
I found that running my present version from RAMDRIVE the two , or so ,
disk accesses are hardly noticable.
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