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Seemingly unused edef prior to an ifx mysteriously affects the outcome of the ifx. Why?

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Seemingly unused edef prior to an ifx mysteriously affects the outcome of the ifx. Why?

Why does this simple ifx test fail?How to display some text based on a condition inside a tabular environment?Macro to do nothing via a defPreserving (and Controlling) ExpandednessWhy does this use of `expandafter` not work?Pre-expansion of moving macro argumentUsing MakeUppercase on expanded macro with argumentDefining an anaphoric macro to define multiple commands based on a templatestoring snapshot of a rapidly changing commandThe laws of expansion (chardeffoo=<number>foo)Why can I not use string to prevent the expansion of csname?

3

It is my understanding that in ifxxy xx else yy fi, ifx does NOT expand its arguments. If you want ifx to compare the expanded values of x and y, then we need to do the expansion ourselves before feeding them to ifx:

edefxpndX{x}

edefxpndY{y}

ifxxpndXxpndY xx else yy fi

asedef does this expansion for us. This is frequently the case when x and y are the arguments in a macro so we really have no idea what kind of quantity they represent.

I was adapting a code snippet I found in user2478's answer to the TeX-SE question Why does this simple ifx test fail? and came up with the following MWE:

documentclass{article}

usepackage[svgnames]{xcolor} % to get named colors



begin{document}



chardefmysteryletter=`H

% loop through A-Z to find out the mystery letter

newcountcurrentchar



currentchar=`A

loop

  chardeftemp=thecurrentchar

  edeftmp{temp}%

  ifxmysterylettertemp {color{Red}bftemp}elsetempfi

  advance currentchar by 1

  unlessifnum currentchar>90

repeat



end{document}

which, when compiled, generated the output:

which actually is the desired output, but it should NOT have been! I added the statement edeftmp{temp} to get the 'expanded' version of temp intending to change the temp argument to the ifx command to tmp but had not when this document was compiled. Low and behold, the desired result was printed out! This lead me to believe that the expansion performed by the edeftmp{temp} statement was not required, so it was commented out and the document recompiled. This gave the wrong result; the letter H was not bold or red

I note that removing the comment character from the end of the edef command had the expected affect of adding a space between each letter, but did not prevent the 'H' from being found and highlighted.

So my question is this: How does the unused expansion of temp by the edef statement change the comparison performed by the ifx command? What am I missing here?

macros conditionals expansion

share|improve this question

edited 1 hour ago

David Carlisle

501k4211481897

asked 2 hours ago

OneMugOneMug

163

New contributor

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add a comment | 

3

It is my understanding that in ifxxy xx else yy fi, ifx does NOT expand its arguments. If you want ifx to compare the expanded values of x and y, then we need to do the expansion ourselves before feeding them to ifx:

edefxpndX{x}

edefxpndY{y}

ifxxpndXxpndY xx else yy fi

asedef does this expansion for us. This is frequently the case when x and y are the arguments in a macro so we really have no idea what kind of quantity they represent.

I was adapting a code snippet I found in user2478's answer to the TeX-SE question Why does this simple ifx test fail? and came up with the following MWE:

documentclass{article}

usepackage[svgnames]{xcolor} % to get named colors



begin{document}



chardefmysteryletter=`H

% loop through A-Z to find out the mystery letter

newcountcurrentchar



currentchar=`A

loop

  chardeftemp=thecurrentchar

  edeftmp{temp}%

  ifxmysterylettertemp {color{Red}bftemp}elsetempfi

  advance currentchar by 1

  unlessifnum currentchar>90

repeat



end{document}

which, when compiled, generated the output:

which actually is the desired output, but it should NOT have been! I added the statement edeftmp{temp} to get the 'expanded' version of temp intending to change the temp argument to the ifx command to tmp but had not when this document was compiled. Low and behold, the desired result was printed out! This lead me to believe that the expansion performed by the edeftmp{temp} statement was not required, so it was commented out and the document recompiled. This gave the wrong result; the letter H was not bold or red

I note that removing the comment character from the end of the edef command had the expected affect of adding a space between each letter, but did not prevent the 'H' from being found and highlighted.

So my question is this: How does the unused expansion of temp by the edef statement change the comparison performed by the ifx command? What am I missing here?

macros conditionals expansion

share|improve this question

edited 1 hour ago

David Carlisle

501k4211481897

asked 2 hours ago

OneMugOneMug

163

New contributor

OneMug is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

It is my understanding that in ifxxy xx else yy fi, ifx does NOT expand its arguments. If you want ifx to compare the expanded values of x and y, then we need to do the expansion ourselves before feeding them to ifx:

edefxpndX{x}

edefxpndY{y}

ifxxpndXxpndY xx else yy fi

asedef does this expansion for us. This is frequently the case when x and y are the arguments in a macro so we really have no idea what kind of quantity they represent.

I was adapting a code snippet I found in user2478's answer to the TeX-SE question Why does this simple ifx test fail? and came up with the following MWE:

documentclass{article}

usepackage[svgnames]{xcolor} % to get named colors



begin{document}



chardefmysteryletter=`H

% loop through A-Z to find out the mystery letter

newcountcurrentchar



currentchar=`A

loop

  chardeftemp=thecurrentchar

  edeftmp{temp}%

  ifxmysterylettertemp {color{Red}bftemp}elsetempfi

  advance currentchar by 1

  unlessifnum currentchar>90

repeat



end{document}

which, when compiled, generated the output:

which actually is the desired output, but it should NOT have been! I added the statement edeftmp{temp} to get the 'expanded' version of temp intending to change the temp argument to the ifx command to tmp but had not when this document was compiled. Low and behold, the desired result was printed out! This lead me to believe that the expansion performed by the edeftmp{temp} statement was not required, so it was commented out and the document recompiled. This gave the wrong result; the letter H was not bold or red

I note that removing the comment character from the end of the edef command had the expected affect of adding a space between each letter, but did not prevent the 'H' from being found and highlighted.

So my question is this: How does the unused expansion of temp by the edef statement change the comparison performed by the ifx command? What am I missing here?

macros conditionals expansion

share|improve this question

edited 1 hour ago

David Carlisle

501k4211481897

asked 2 hours ago

OneMugOneMug

163

New contributor

OneMug is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edefxpndX{x}

edefxpndY{y}

ifxxpndXxpndY xx else yy fi

documentclass{article}

usepackage[svgnames]{xcolor} % to get named colors



begin{document}



chardefmysteryletter=`H

% loop through A-Z to find out the mystery letter

newcountcurrentchar



currentchar=`A

loop

  chardeftemp=thecurrentchar

  edeftmp{temp}%

  ifxmysterylettertemp {color{Red}bftemp}elsetempfi

  advance currentchar by 1

  unlessifnum currentchar>90

repeat



end{document}

share|improve this question

edited 1 hour ago

David Carlisle

501k4211481897

asked 2 hours ago

OneMugOneMug

163

New contributor

OneMug is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 1 hour ago

David Carlisle

501k4211481897

asked 2 hours ago

OneMugOneMug

163

New contributor

OneMug is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edited 1 hour ago

David Carlisle

501k4211481897

edited 1 hour ago

David Carlisle

501k4211481897

asked 2 hours ago

OneMugOneMug

163

New contributor

OneMug is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 2 hours ago

OneMugOneMug

163

1 Answer
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4

  chardeftemp=thecurrentchar

  edeftmp{temp}%

tokens defined via chardef are not expandable, so edeftmp{temp} is the same as deftmp{temp}

It is not clear why you do not expect ifxmysterylettertemp not to be true if the two tokens are both defined via chardef with the same number?

I guess your modified version was equivalent to

  chardeftemp=thecurrentchar

  ifxmysterylettertemp 

There the ifx test happens before the assignment while looking to end the number, you need

  chardeftemp=thecurrentcharrelax

  ifxmysterylettertemp 

or

  chardeftemp=currentchar

  ifxmysterylettertemp 

So your edef was just acting like relax terminating the chardef assignment.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

David CarlisleDavid Carlisle

501k4211481897

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the fast response. Still trying to figure out how to use the TeX-SE question and comment editors, please be patient. I had planned on converting this snippet into a defscanAlpha#1{... so I coded it the way I did expecting the macro argument to be used in the ifx to be somewhat unknown at execution time, say be using scanAlpha{X} which would make the argument to the ifx different from using the chardef as in the snippet.
  
  – OneMug
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  As stated, removing the edef and using either chardeftemp=thecurrentcharrelax or chardeftemp=currentchar works just fine. Aah, such are the mysteries of relaxing. Not sure if I will ever figure out how to relax. Thanks again for this answer.
  
  – OneMug
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @OneMugit'its not really the relax just that expansion happens when looking for a number, count0=1ifx ab 2else 3fi sets count0 to 13 with the ifx test happening before the assignment, but count0=1 ifx ab 2else 3fi sets count0 to 1
  
  – David Carlisle
  51 mins ago
  
  
  

  
  
  
  

add a comment | 

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4

  chardeftemp=thecurrentchar

  edeftmp{temp}%

tokens defined via chardef are not expandable, so edeftmp{temp} is the same as deftmp{temp}

It is not clear why you do not expect ifxmysterylettertemp not to be true if the two tokens are both defined via chardef with the same number?

I guess your modified version was equivalent to

  chardeftemp=thecurrentchar

  ifxmysterylettertemp 

There the ifx test happens before the assignment while looking to end the number, you need

  chardeftemp=thecurrentcharrelax

  ifxmysterylettertemp 

or

  chardeftemp=currentchar

  ifxmysterylettertemp 

So your edef was just acting like relax terminating the chardef assignment.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

David CarlisleDavid Carlisle

501k4211481897

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the fast response. Still trying to figure out how to use the TeX-SE question and comment editors, please be patient. I had planned on converting this snippet into a defscanAlpha#1{... so I coded it the way I did expecting the macro argument to be used in the ifx to be somewhat unknown at execution time, say be using scanAlpha{X} which would make the argument to the ifx different from using the chardef as in the snippet.
  
  – OneMug
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  As stated, removing the edef and using either chardeftemp=thecurrentcharrelax or chardeftemp=currentchar works just fine. Aah, such are the mysteries of relaxing. Not sure if I will ever figure out how to relax. Thanks again for this answer.
  
  – OneMug
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @OneMugit'its not really the relax just that expansion happens when looking for a number, count0=1ifx ab 2else 3fi sets count0 to 13 with the ifx test happening before the assignment, but count0=1 ifx ab 2else 3fi sets count0 to 1
  
  – David Carlisle
  51 mins ago
  
  
  

  
  
  
  

add a comment | 

4

  chardeftemp=thecurrentchar

  edeftmp{temp}%

tokens defined via chardef are not expandable, so edeftmp{temp} is the same as deftmp{temp}

It is not clear why you do not expect ifxmysterylettertemp not to be true if the two tokens are both defined via chardef with the same number?

I guess your modified version was equivalent to

  chardeftemp=thecurrentchar

  ifxmysterylettertemp 

There the ifx test happens before the assignment while looking to end the number, you need

  chardeftemp=thecurrentcharrelax

  ifxmysterylettertemp 

or

  chardeftemp=currentchar

  ifxmysterylettertemp 

So your edef was just acting like relax terminating the chardef assignment.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

David CarlisleDavid Carlisle

501k4211481897

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the fast response. Still trying to figure out how to use the TeX-SE question and comment editors, please be patient. I had planned on converting this snippet into a defscanAlpha#1{... so I coded it the way I did expecting the macro argument to be used in the ifx to be somewhat unknown at execution time, say be using scanAlpha{X} which would make the argument to the ifx different from using the chardef as in the snippet.
  
  – OneMug
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  As stated, removing the edef and using either chardeftemp=thecurrentcharrelax or chardeftemp=currentchar works just fine. Aah, such are the mysteries of relaxing. Not sure if I will ever figure out how to relax. Thanks again for this answer.
  
  – OneMug
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @OneMugit'its not really the relax just that expansion happens when looking for a number, count0=1ifx ab 2else 3fi sets count0 to 13 with the ifx test happening before the assignment, but count0=1 ifx ab 2else 3fi sets count0 to 1
  
  – David Carlisle
  51 mins ago
  
  
  

  
  
  
  

add a comment | 

  chardeftemp=thecurrentchar

  edeftmp{temp}%

tokens defined via chardef are not expandable, so edeftmp{temp} is the same as deftmp{temp}

It is not clear why you do not expect ifxmysterylettertemp not to be true if the two tokens are both defined via chardef with the same number?

I guess your modified version was equivalent to

  chardeftemp=thecurrentchar

  ifxmysterylettertemp 

There the ifx test happens before the assignment while looking to end the number, you need

  chardeftemp=thecurrentcharrelax

  ifxmysterylettertemp 

or

  chardeftemp=currentchar

  ifxmysterylettertemp 

So your edef was just acting like relax terminating the chardef assignment.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

David CarlisleDavid Carlisle

501k4211481897

  chardeftemp=thecurrentchar

  edeftmp{temp}%

  chardeftemp=thecurrentchar

  ifxmysterylettertemp 

  chardeftemp=thecurrentcharrelax

  ifxmysterylettertemp 

  chardeftemp=currentchar

  ifxmysterylettertemp 

share|improve this answer

edited 1 hour ago

answered 1 hour ago

David CarlisleDavid Carlisle

501k4211481897

answered 1 hour ago

David CarlisleDavid Carlisle

501k4211481897

answered 1 hour ago

David CarlisleDavid Carlisle

501k4211481897