LaTeX reader: \hspace and \vspace do not parse decimal point.

[mcourteaux]

Explain the problem.

pandoc -f latex -t typst --verbose
$A\hspace{0.4em}B$
^D

yields:

[WARNING] Could not convert TeX math A\hspace{0.4em}B, rendering as TeX:
  A\hspace{0.4em}B
            ^
  unexpected "."
  expecting digit, "em", "pt", "in" or "cm"
\$A\\hspace{0.4em}B\$

Note that using integers does work: using 1em yields quad in the Typst output.

Pandoc version?
3.6.3 / Linux

[mcourteaux]

Playing with the online demo for texmath, I saw that negative numbers also don't parse. I sometimes use this to fiddle with the layout of a formula. Although most of the time, I rely on \; for that.

[mcourteaux]

As a workaround, I wrote a lua filter that replaces these lengths with an integer equivalent in expressed in pt. While trying that, I noticed that other length units are also not supported (such as mu). I found the source for parsing a length, and that supports all those things, so it seems that hspace and vspace use a different parser.

texmath/src/Text/TeXMath/Readers/TeX.hs

Lines 719 to 730 in 6bc4771

	xspace "\\hspace" = do
	braces $ do
	len <- many1 digit
	scaleFactor <-
	1 <$ (string "em")
	<|> (1/12) <$ (string "pt")
	<|> 6 <$ (string "in")
	<|> (50/21) <$ (string "cm")
	case reads len of
	((n :: Integer,[]):_) -> return $ ESpace (fromIntegral n * scaleFactor)
	_ -> mzero
	xspace _ = mzero

Is repeated code, instead of using:

texmath/src/Text/TeXMath/Shared.hs

Lines 162 to 179 in 6bc4771

	readLength :: T.Text -> Maybe Rational
	readLength s = do
	(n, unit) <- case (parse parseLength "" s) of
	Left _ -> Nothing
	Right v -> Just v
	(n *) <$> unitToMultiplier unit
	parseLength :: Parsec T.Text () (Rational, T.Text)
	parseLength = do
	neg <- option "" ((:[]) <$> char '-')
	dec <- many1 digit
	frac <- option "" ((:) <$> char '.' <*> many1 digit)
	unit <- getInput
	-- This is safe as dec and frac must be a double of some kind
	case reads (neg ++ dec ++ frac) of
	[(n :: Double, [])] -> return (round (n * 18) % 18, unit)
	_ -> fail $ "Could not parse " ++ neg ++ dec ++ frac ++ " as Double"

[jgm]

\vspace isn't supported at all. (No corresponding AST element.)
mu is supported but only in \mspace. Does it work with hspace too? (No, it turns out.)

PS. the online demo is probably several versions behind.

[jgm]

Decimals in \hspace are now fixed.

[jgm]

Negative numbers are not supported, so I'll reopen this for that.