YuruMath

YuruMath is an implementation of the TeX language (without a complete visual processor) in Haskell. This is developed with the intention to emit MathML from (La)TeX formula.

Play with REPL

$ git clone https://github.com/minoki/yurumath.git
$ cd yurumath/
$ stack build --fast
$ stack exec yurumath-repl
*

* is the prompt (as in TeX).

Now let's type something:

*\message{Hello world!}
Hello world!
*

Some equation:

*\frac{a}{b}
MathML: <math>
    <mfrac>
        <mi>
            a
        </mi>
        <mi>
            b
        </mi>
    </mfrac>
</math>

*

Integers beyond 2³² are supported:

*\def\fact#1{\ifnum#1=0 1 \else\numexpr#1*\expandafter\fact\expandafter{\number\numexpr#1-1\relax}\relax\fi}
*\message{\number\fact{20}}
2432902008176640000
*\message{\number"100000000 }
4294967296

The interpreter tries to prevent infinite loop:

*\def\foo{\foo} \foo
error: recursion too deep
*\def\foo{\foo\foo\foo} \foo
error: token list too long
*\def\foo{\uppercase{\foo}} \foo
error: recursion too deep
*\def\foo{'} {\catcode`\'=\active \global\let'=\foo} '
error: recursion too deep

Supported TeX primitives

Some commands are from e-TeX or XeTeX/LuaTeX.

Expandable commands

• \expandafter, \noexpand, \csname, \string, \number, \romannumeral, \the, \meaning
• \if, \ifcat, \ifx, \iftrue, \iffalse, \ifnum, \ifdim, \ifodd, \ifcase
• \ifhmode, \ifvmode, \ifmmode, \ifinner, \ifdefined, \ifcsname, \ifabsnum, \ifincsname
• \unless, \else, \fi, \or
• \begincsname, \csstring, \Uchar, \mathstyle
• \unexpanded, \detokenize, \scantokens, \strcmp (or \pdfstrcmp), \expanded

Non-expandable commands

• \relax, \endcsname, \global
• \uppercase, \lowercase, \ignorespaces
• \let, \futurelet
• \def, \edef, \gdef, \xdef, \outer, \long, \protected
• \chardef, \mathchardef, \Umathchardef, \Umathcharnumdef
• \catcode, \lccode, \uccode, \mathcode, \Umathcode, \Umathcodenum, \delcode, \Udelcode, \Udelcodenum
• \begingroup, \endgroup
• \endlinechar, \escapechar
• \count, \countdef, \dimen, \dimendef, \skip, \skipdef, \muskip, \muskipdef, \toks, \toksdef
• \advance, \multiply, \divide
• \numexpr, \dimexpr, \glueexpr, \muexpr
• \gluestretch, \glueshrink, \gluestretchorder, \glueshrinkorder, \mutoglue, \gluetomu
• \message, \show, \showthe, \showtokens
• \char, \kern, \unkern, \unskip, \hskip, \hfil, \hfill, \hss, \hfilneg, \noindent, \ , \/
• \newcommand, \renewcommand, \providecommand (from LaTeX)

Math mode commands:

• \mathchar, \Umathchar, \Umathcharnum, \delimiter, \Udelimiter, \mathaccent, \Umathaccent, \radical, \Uradical, \Uroot
• \mathord, \mathop, \mathbin, \mathrel, \mathopen, \mathclose, \mathpunct, \mathinner
• \underline, \overline, \vcenter
• \displaylimits, \limits, \nolimits
• \left, \middle, \right, \Uleft, \Umiddle, \Uright
• \over, \atop, \above, \Uskewed, \overwithdelims, \atopwithdelims, \abovewithdelims, \Uskewedwithdelims
• \mathchoice, \Ustack
• \fam, \thinmuskip, \medmuskip, \thickmuskip
• \mkern, \mskip, \nonscript
• \Usuperscript, \Usubscript, \Ustopmath, \Ustopdisplaymath
• \displaystyle, \textstyle, \scriptstyle, \scriptscriptstyle, \crampeddisplaystyle, \crampedtextstyle, \crampedscriptstyle, \crampedscriptscriptstyle

Incompatiblities with TeX

• \over-like commands must be prefixed by \Ustack, like \Ustack{1\over2}.
• ^^ notation in the control word (e.g. \f^^6fo = \foo) is not allowed.
• Expansion of \noexpand yields a token whose meaning is really equivalent to \relax; That is, \expandafter\let\expandafter\foo\noexpand\baz \ifx\foo\relax\message{Y}\else\message{N}\fi prints Y in YuruMath, whereas it prints N in a real TeX.
• The \relax inserted by \or, \else or \fi is equivalent to a control sequence named relax whose meaning is \relax; That is, \def\foo\relax{} \expandafter\foo\ifodd1\fi produces no error in YuruMath, whereas it raises the error Use of \foo doesn't match its definition. in a real TeX.