On Tue, 22 Dec 2015, Alan BRASLAU wrote:
Wolfgang,
Can you explain to us why it should be preferable for ConTeXt users to
employ \frac12 rather than the native TeX construction {1\over 2}?
I understand that the macro \frac does some additional trickery but the
two constructions should *always* yield identical results (when
keyed-in properly).
One of the troubles with { .... \over ...} and the like is that TeX does
not know which "style" to use. This can lead to extra processing when
using any command defined using \mathpalatte (such as \text, stacked
arrows, and others).
Consider \text{...}. Basically, we want \text{...} to typeset it's
argument in a \hbox with textsize equal to the normalsize in normal mode
and equal to script size when used in a subscript and in scriptsciptsize
when used in a sub-subscript. Now, in traditional tex, when parsing
{\text{hello} \over 2}
TeX does not kow what size to use for \text{...} until it encounters the
\over. So, when parsing \text{hello}, TeX generates all possible sizes and
then prunes them later on. With nested constructs like
{\text{hello}_{\text{world} \over 2} \over 2}
it can lead to exponential number of branches.
With \frac{\text{hello}}{2}, TeX "knows" what style to use for the
arguments. So, extra processing is not needed (at least, this is the idea
in LuaTeX; in PDFTeX, multiple sizes need to be generated). This can lead
to some slightly faster processing.
Also see http://tex.stackexchange.com/a/1261/ answer from Taco. Contrast
the definition of \cramped given there from one in the LaTeX mathtools
package
(http://ctan.bppro.ca/macros/latex/contrib/mathtools/mathtools.dtx)
[search from MT_cramped_clap_internal:Nn]
Aditya
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