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Expansion of ifnum creates a weird relax token
Expansion of first token in a tabular cellExpansion in numexpr…relax versus pdfstrcmpNormal relax vs. frozen relaxWhat is wrong with ifnum#1=0.09relax?Use of relax after ifnum … fi constructionIs implicit `relax` in conditionals explained anywhere in the TeXbook?Understanding token expansionweird ifnum with compact syntaxifnum and expansion of macro argumentifx doesn't treat noexpand as relax
There was I, procrastinating over some TeX code while I should have been writing my dissertation. The code was working more or less fine (better than the writing, at least), until a mysterious relax popped up from nowhere!
At first I though it was something stupid from my end, but when I reduced the code to a bare minimum I realised I had no idea what was going on. I reduced the code to use basically only primitives, so it shouldn't be any coding problem. Here's the guilty code:
defuseIInnn#1#2#3#2
defuseIInn#1#2#2
detokenizeexpandafterifnum0=0expandafteruseIInnnfiuseIInn1BOOM
bye
and its output is (surprisingly, for me):
relax fi 1BOOM
Where did that relax come from?
I realise that the test wouldn't result in 0=0 because ifnum would continue expanding tokens (as far as I understand, it would make 0=01 and result false; I corrected this in the code :). However the relax remains a mystery for me.
tex-core conditionals expansion
asked May 11 at 13:28
Phelype OleinikPhelype Oleinik
27.5k54793
add a comment |
There was I, procrastinating over some TeX code while I should have been writing my dissertation. The code was working more or less fine (better than the writing, at least), until a mysterious relax popped up from nowhere!
At first I though it was something stupid from my end, but when I reduced the code to a bare minimum I realised I had no idea what was going on. I reduced the code to use basically only primitives, so it shouldn't be any coding problem. Here's the guilty code:
defuseIInnn#1#2#3#2
defuseIInn#1#2#2
detokenizeexpandafterifnum0=0expandafteruseIInnnfiuseIInn1BOOM
bye
and its output is (surprisingly, for me):
relax fi 1BOOM
Where did that relax come from?
I realise that the test wouldn't result in 0=0 because ifnum would continue expanding tokens (as far as I understand, it would make 0=01 and result false; I corrected this in the code :). However the relax remains a mystery for me.
tex-core conditionals expansion
asked May 11 at 13:28
Phelype OleinikPhelype Oleinik
27.5k54793
add a comment |
There was I, procrastinating over some TeX code while I should have been writing my dissertation. The code was working more or less fine (better than the writing, at least), until a mysterious relax popped up from nowhere!
At first I though it was something stupid from my end, but when I reduced the code to a bare minimum I realised I had no idea what was going on. I reduced the code to use basically only primitives, so it shouldn't be any coding problem. Here's the guilty code:
defuseIInnn#1#2#3#2
defuseIInn#1#2#2
detokenizeexpandafterifnum0=0expandafteruseIInnnfiuseIInn1BOOM
bye
and its output is (surprisingly, for me):
relax fi 1BOOM
Where did that relax come from?
I realise that the test wouldn't result in 0=0 because ifnum would continue expanding tokens (as far as I understand, it would make 0=01 and result false; I corrected this in the code :). However the relax remains a mystery for me.
tex-core conditionals expansion
asked May 11 at 13:28
Phelype OleinikPhelype Oleinik
27.5k54793
There was I, procrastinating over some TeX code while I should have been writing my dissertation. The code was working more or less fine (better than the writing, at least), until a mysterious relax popped up from nowhere!
At first I though it was something stupid from my end, but when I reduced the code to a bare minimum I realised I had no idea what was going on. I reduced the code to use basically only primitives, so it shouldn't be any coding problem. Here's the guilty code:
defuseIInnn#1#2#3#2
defuseIInn#1#2#2
detokenizeexpandafterifnum0=0expandafteruseIInnnfiuseIInn1BOOM
bye
and its output is (surprisingly, for me):
relax fi 1BOOM
Where did that relax come from?
I realise that the test wouldn't result in 0=0 because ifnum would continue expanding tokens (as far as I understand, it would make 0=01 and result false; I corrected this in the code :). However the relax remains a mystery for me.
tex-core conditionals expansion
tex-core conditionals expansion
asked May 11 at 13:28
Phelype OleinikPhelype Oleinik
27.5k54793
asked May 11 at 13:28
Phelype OleinikPhelype Oleinik
27.5k54793
asked May 11 at 13:28
Phelype OleinikPhelype Oleinik
27.5k54793
asked May 11 at 13:28
Phelype OleinikPhelype Oleinik
27.5k54793
asked May 11 at 13:28
Phelype OleinikPhelype Oleinik
27.5k54793
27.5k54793
add a comment |
add a comment |
1 Answer
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Let's see what happens. The tokens ifnum0=0 are not a full test, because by rule TeX expands tokens until either finding an unexpandable token that cannot be interpreted as a digit; if this token is a space, it will be swallowed.
The token following 0 is expandafter, which expands the fi: oh, this means that the conditional has to be evaluated! In such cases, that is, whenever a conditional text is unfinished at the time else or fi appear and have to be expanded, TeX inserts a special relax token, called frozen relax.
You get a frozen relax also in cases such as if xfi; two in the case of iffi.
This is module 379 in tex.web.
answered May 11 at 13:36
egregegreg
741k8919423274
Hm, cool, it's a type of safety. It's easy to see therelaxes appearing withunravelexpandafteriffi(I actually saw it earlier, but it didn't make sense). Thanks :-)
– Phelype Oleinik
May 11 at 13:48
add a comment |
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Let's see what happens. The tokens ifnum0=0 are not a full test, because by rule TeX expands tokens until either finding an unexpandable token that cannot be interpreted as a digit; if this token is a space, it will be swallowed.
The token following 0 is expandafter, which expands the fi: oh, this means that the conditional has to be evaluated! In such cases, that is, whenever a conditional text is unfinished at the time else or fi appear and have to be expanded, TeX inserts a special relax token, called frozen relax.
You get a frozen relax also in cases such as if xfi; two in the case of iffi.
This is module 379 in tex.web.
answered May 11 at 13:36
egregegreg
741k8919423274
Hm, cool, it's a type of safety. It's easy to see therelaxes appearing withunravelexpandafteriffi(I actually saw it earlier, but it didn't make sense). Thanks :-)
– Phelype Oleinik
May 11 at 13:48
add a comment |
Let's see what happens. The tokens ifnum0=0 are not a full test, because by rule TeX expands tokens until either finding an unexpandable token that cannot be interpreted as a digit; if this token is a space, it will be swallowed.
The token following 0 is expandafter, which expands the fi: oh, this means that the conditional has to be evaluated! In such cases, that is, whenever a conditional text is unfinished at the time else or fi appear and have to be expanded, TeX inserts a special relax token, called frozen relax.
You get a frozen relax also in cases such as if xfi; two in the case of iffi.
This is module 379 in tex.web.
answered May 11 at 13:36
egregegreg
741k8919423274
Hm, cool, it's a type of safety. It's easy to see therelaxes appearing withunravelexpandafteriffi(I actually saw it earlier, but it didn't make sense). Thanks :-)
– Phelype Oleinik
May 11 at 13:48
add a comment |
Let's see what happens. The tokens ifnum0=0 are not a full test, because by rule TeX expands tokens until either finding an unexpandable token that cannot be interpreted as a digit; if this token is a space, it will be swallowed.
The token following 0 is expandafter, which expands the fi: oh, this means that the conditional has to be evaluated! In such cases, that is, whenever a conditional text is unfinished at the time else or fi appear and have to be expanded, TeX inserts a special relax token, called frozen relax.
You get a frozen relax also in cases such as if xfi; two in the case of iffi.
This is module 379 in tex.web.
answered May 11 at 13:36
egregegreg
741k8919423274
Let's see what happens. The tokens ifnum0=0 are not a full test, because by rule TeX expands tokens until either finding an unexpandable token that cannot be interpreted as a digit; if this token is a space, it will be swallowed.
The token following 0 is expandafter, which expands the fi: oh, this means that the conditional has to be evaluated! In such cases, that is, whenever a conditional text is unfinished at the time else or fi appear and have to be expanded, TeX inserts a special relax token, called frozen relax.
You get a frozen relax also in cases such as if xfi; two in the case of iffi.
This is module 379 in tex.web.
answered May 11 at 13:36
egregegreg
741k8919423274
answered May 11 at 13:36
egregegreg
741k8919423274
answered May 11 at 13:36
egregegreg
741k8919423274
answered May 11 at 13:36
egregegreg
741k8919423274
741k8919423274
Hm, cool, it's a type of safety. It's easy to see therelaxes appearing withunravelexpandafteriffi(I actually saw it earlier, but it didn't make sense). Thanks :-)
– Phelype Oleinik
May 11 at 13:48
add a comment |
Hm, cool, it's a type of safety. It's easy to see therelaxes appearing withunravelexpandafteriffi(I actually saw it earlier, but it didn't make sense). Thanks :-)
– Phelype Oleinik
May 11 at 13:48
Hm, cool, it's a type of safety. It's easy to see the
relaxes appearing with unravelexpandafteriffi (I actually saw it earlier, but it didn't make sense). Thanks :-)– Phelype Oleinik
May 11 at 13:48
Hm, cool, it's a type of safety. It's easy to see the
relaxes appearing with unravelexpandafteriffi (I actually saw it earlier, but it didn't make sense). Thanks :-)– Phelype Oleinik
May 11 at 13:48
add a comment |
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