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Use of noexpand in the implementation of TextOrMath for eTeX


When to use edef, noexpand, and expandafter?Does noexpand have to be a primitive?Problem with nested noexpand and edefReplacement for unexpanded without eTeX extensionWhy do some arguments in a macro need to be preceded by noexpand?How to use noexpand in an edef?Why six noexpand in a row?How can I use noexpand and unexpanded without appending a space to the unexpanded tokens?How should I /protect this command for use in csname?ifx doesn't treat noexpand as relax













4















In latexrelease 2015/01/01, there are two implementations of TextOrMath: one for regular
TeX, the other one for eTeX-like engines (more precisely: those which support protected). My question concerns the latter:



protectedexpandafterdefcsname TextOrMathspaceendcsname{%
(...) } % no problem here
edefTextOrMath#1#2{% from latex.ltx
expandafternoexpandcsname TextOrMathspaceendcsname
{#1}{#2}}


I think I understand well these definitions, however I can't figure out why the edef isn't simply written this way:



edefTextOrMath#1#2{% from me
csname TextOrMathspaceendcsname
{#1}{#2}}


Since the internal TextOrMath<space> macro is protected, what is the point of preceding it with noexpand inside the edef? Is it because the author feared that protected might be deficient?..



I made a test like this (ran with pdfTeX):



% From latex.ltx (or p. 153 of source2e.pdf)
protectedexpandafterdefcsname TextOrMathspaceendcsname{%
ifmmode expandafter@secondoftwo
else expandafter@firstoftwo fi}

edefTextOrMath#1#2{%
expandafternoexpandcsname TextOrMathspaceendcsname
{#1}{#2}}

% My simpler way of doing the same (?)
edefaltTextOrMath#1#2{%
csname TextOrMathspaceendcsname
{#1}{#2}}

showTextOrMath % TextOrMath=macro:#1#2->TextOrMath {#1}{#2}.
showaltTextOrMath % altTextOrMath=ditto

ifxTextOrMathaltTextOrMath
identical
else
different
fi

vfill
eject
bye


This test prints 'identical' and seems to indicate that my definition is equivalent to the one in latex.ltx (but slightly simpler). Did I miss something?



Thanks!










share|improve this question























  • thanks I suppose we could change that:-)

    – David Carlisle
    4 hours ago











  • Many thanks for your insight into this, I was really puzzled!

    – frougon
    4 hours ago
















4















In latexrelease 2015/01/01, there are two implementations of TextOrMath: one for regular
TeX, the other one for eTeX-like engines (more precisely: those which support protected). My question concerns the latter:



protectedexpandafterdefcsname TextOrMathspaceendcsname{%
(...) } % no problem here
edefTextOrMath#1#2{% from latex.ltx
expandafternoexpandcsname TextOrMathspaceendcsname
{#1}{#2}}


I think I understand well these definitions, however I can't figure out why the edef isn't simply written this way:



edefTextOrMath#1#2{% from me
csname TextOrMathspaceendcsname
{#1}{#2}}


Since the internal TextOrMath<space> macro is protected, what is the point of preceding it with noexpand inside the edef? Is it because the author feared that protected might be deficient?..



I made a test like this (ran with pdfTeX):



% From latex.ltx (or p. 153 of source2e.pdf)
protectedexpandafterdefcsname TextOrMathspaceendcsname{%
ifmmode expandafter@secondoftwo
else expandafter@firstoftwo fi}

edefTextOrMath#1#2{%
expandafternoexpandcsname TextOrMathspaceendcsname
{#1}{#2}}

% My simpler way of doing the same (?)
edefaltTextOrMath#1#2{%
csname TextOrMathspaceendcsname
{#1}{#2}}

showTextOrMath % TextOrMath=macro:#1#2->TextOrMath {#1}{#2}.
showaltTextOrMath % altTextOrMath=ditto

ifxTextOrMathaltTextOrMath
identical
else
different
fi

vfill
eject
bye


This test prints 'identical' and seems to indicate that my definition is equivalent to the one in latex.ltx (but slightly simpler). Did I miss something?



Thanks!










share|improve this question























  • thanks I suppose we could change that:-)

    – David Carlisle
    4 hours ago











  • Many thanks for your insight into this, I was really puzzled!

    – frougon
    4 hours ago














4












4








4








In latexrelease 2015/01/01, there are two implementations of TextOrMath: one for regular
TeX, the other one for eTeX-like engines (more precisely: those which support protected). My question concerns the latter:



protectedexpandafterdefcsname TextOrMathspaceendcsname{%
(...) } % no problem here
edefTextOrMath#1#2{% from latex.ltx
expandafternoexpandcsname TextOrMathspaceendcsname
{#1}{#2}}


I think I understand well these definitions, however I can't figure out why the edef isn't simply written this way:



edefTextOrMath#1#2{% from me
csname TextOrMathspaceendcsname
{#1}{#2}}


Since the internal TextOrMath<space> macro is protected, what is the point of preceding it with noexpand inside the edef? Is it because the author feared that protected might be deficient?..



I made a test like this (ran with pdfTeX):



% From latex.ltx (or p. 153 of source2e.pdf)
protectedexpandafterdefcsname TextOrMathspaceendcsname{%
ifmmode expandafter@secondoftwo
else expandafter@firstoftwo fi}

edefTextOrMath#1#2{%
expandafternoexpandcsname TextOrMathspaceendcsname
{#1}{#2}}

% My simpler way of doing the same (?)
edefaltTextOrMath#1#2{%
csname TextOrMathspaceendcsname
{#1}{#2}}

showTextOrMath % TextOrMath=macro:#1#2->TextOrMath {#1}{#2}.
showaltTextOrMath % altTextOrMath=ditto

ifxTextOrMathaltTextOrMath
identical
else
different
fi

vfill
eject
bye


This test prints 'identical' and seems to indicate that my definition is equivalent to the one in latex.ltx (but slightly simpler). Did I miss something?



Thanks!










share|improve this question














In latexrelease 2015/01/01, there are two implementations of TextOrMath: one for regular
TeX, the other one for eTeX-like engines (more precisely: those which support protected). My question concerns the latter:



protectedexpandafterdefcsname TextOrMathspaceendcsname{%
(...) } % no problem here
edefTextOrMath#1#2{% from latex.ltx
expandafternoexpandcsname TextOrMathspaceendcsname
{#1}{#2}}


I think I understand well these definitions, however I can't figure out why the edef isn't simply written this way:



edefTextOrMath#1#2{% from me
csname TextOrMathspaceendcsname
{#1}{#2}}


Since the internal TextOrMath<space> macro is protected, what is the point of preceding it with noexpand inside the edef? Is it because the author feared that protected might be deficient?..



I made a test like this (ran with pdfTeX):



% From latex.ltx (or p. 153 of source2e.pdf)
protectedexpandafterdefcsname TextOrMathspaceendcsname{%
ifmmode expandafter@secondoftwo
else expandafter@firstoftwo fi}

edefTextOrMath#1#2{%
expandafternoexpandcsname TextOrMathspaceendcsname
{#1}{#2}}

% My simpler way of doing the same (?)
edefaltTextOrMath#1#2{%
csname TextOrMathspaceendcsname
{#1}{#2}}

showTextOrMath % TextOrMath=macro:#1#2->TextOrMath {#1}{#2}.
showaltTextOrMath % altTextOrMath=ditto

ifxTextOrMathaltTextOrMath
identical
else
different
fi

vfill
eject
bye


This test prints 'identical' and seems to indicate that my definition is equivalent to the one in latex.ltx (but slightly simpler). Did I miss something?



Thanks!







macros expansion definition protected-macro






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 6 hours ago









frougonfrougon

641611




641611













  • thanks I suppose we could change that:-)

    – David Carlisle
    4 hours ago











  • Many thanks for your insight into this, I was really puzzled!

    – frougon
    4 hours ago



















  • thanks I suppose we could change that:-)

    – David Carlisle
    4 hours ago











  • Many thanks for your insight into this, I was really puzzled!

    – frougon
    4 hours ago

















thanks I suppose we could change that:-)

– David Carlisle
4 hours ago





thanks I suppose we could change that:-)

– David Carlisle
4 hours ago













Many thanks for your insight into this, I was really puzzled!

– frougon
4 hours ago





Many thanks for your insight into this, I was really puzzled!

– frougon
4 hours ago










1 Answer
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No you didn't miss anything, just old habits die hard as we gradually add these modern post 1992 features into the sources....






share|improve this answer
























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    3














    No you didn't miss anything, just old habits die hard as we gradually add these modern post 1992 features into the sources....






    share|improve this answer




























      3














      No you didn't miss anything, just old habits die hard as we gradually add these modern post 1992 features into the sources....






      share|improve this answer


























        3












        3








        3







        No you didn't miss anything, just old habits die hard as we gradually add these modern post 1992 features into the sources....






        share|improve this answer













        No you didn't miss anything, just old habits die hard as we gradually add these modern post 1992 features into the sources....







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 4 hours ago









        David CarlisleDavid Carlisle

        497k4111441891




        497k4111441891






























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