Something like this needs a recursive parser. Aside from suggesting Parse::RecDescent or the example in Japhy's book, I'll give a few suggestions on how I would approach this.

First off, you are correct in storing it a tree-type data structure. However, don't use a normal hash; I recommend Tie::IxHash to keep an ordered hash since you will need to reorder later.

Next, you will need to figure out a way of determining whether a term is top level, and separate those terms from each other. Simply splitting on /[+-]/ wont be enough; you'll need to inchworm through in order and determine context. Next, you'll have to separate those terms which are /[*\/]/, and mark those as separate parts of one term. Finally, you'll need to deal with leftovers, such as exponentiation, function calls, etc.

Once you have the top level terms in the tree, you'll have descend into each node and repeat the process (here is where the recursion comes in.) You'll need to do it again, and again, and again, until everything is parsed to its lowest level. Finally, you'll have to work backwards from the bottom to perform the calculations.

Not as easy as you thought, was it? That's why there is CPAN :)

In reply to Re: Seeking Advice: Writing a parser by jryan
in thread Seeking Advice: Writing a parser by Flame

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.