Extensible delimiters (\left and \right)

[gsomix]

Full brace list we need to support:

• \left. \right. (empty delimiter)
• \left( \right)
• \left[ \right]
• \left\{ \right\}
• \left< \right>
• \left| \right|

Plan

• take a look at Java implementation — at least JLatexMath seems to support those delimiters ~ F
• implement delimiters as a resizable characters (i.e. don't split them into top / top-middle / etc. parts yet)
• add full support with splitting the characters into parts — it suddenly turned out that we already have those

[ForNeVeR]

I think that we'll need to store brace stack somewhere when interpreting the formula, and try to keep size of the matching braces equal. Note that different braces could match each one. E.g. \left< \frac{a}{\frac{b}{c}} \right\} should be rendered as .

Here's a good explanation of so-called "extensible delimiters" on StackExchange: http://tex.stackexchange.com/a/77593/109147

[alexreg]

This is definitely a feature that should be prioritised. I'm not sure if the Java library I ported from handled this at all (actually there were two Java libraries; one for plain TeX and one for LaTeX), but it's worth a check. If not, having a look at the LaTeX source code may be informative.

[ForNeVeR]

Aha, it seems like jlatexmath have support for \left and \right.

[ForNeVeR]

Just dumping what I've found regarding this task so far.

It seems that we have the atom definition for the brace-enclosed formula; it's called FencedAtom.

It looks like that FencedAtom isn't used in the current code, but it could be exactly what we need. I plan to add the support for \left and \right commands into TexFormulaParser.ProcessCommand method. It seems like that won't be very hard: just parse the formula part before the corresponding \right command and enclose it in FencedAtom (probably we'll want to keep that stack somewhere; we'll see).

I also want to add unit tests for the parser; I'll file another issue about that.

[alexreg]

Good work on this. I haven't looked at the implementation yet, but I'm slightly concerned that most of the brackets are implemented except for \left|. Did you not do this in a generic way?

[ForNeVeR]

Ah, that's a long story. My initial implementation had some flaws, and I thought there were problems with \left|. Actually there're none.

The delimiters are implemented in a generic way (because there's already a metadata on delimiters), \left| is working. I'll mark it now.

\left. and \right. aren't working currently exactly because there aren't any metadata about them. I think we'll handle them in a special way or simple declare as proper delimiters; will decide later.

[alexreg]

Oh, right. Fair enough then!

[alexreg]

I just noticed that \left| and \right| still don't work.

[ForNeVeR]

Oh, that's interesting. | is considered as an opening delimiter only. Look:

[alexreg]

Good spot. That was definitely the problem.