LaTeX: Why are digits allowed in environments, but forbidden in commands?
Finding out that I can have an environment named env2, but no command cmd2, I read Why are some characters not allowed in command sequences, but still I wonder:
Why are digits allowed in environments, but forbidden in commands? In my understanding digits delimit command names (inherited from plain TeX), but why doesn't that restriction apply to environments? Wouldn't it have been more consistent to forbid digits in environment names as well?
macros environments
asked Apr 5 at 22:32
U. WindlU. Windl
1718
add a comment |
Finding out that I can have an environment named env2, but no command cmd2, I read Why are some characters not allowed in command sequences, but still I wonder:
Why are digits allowed in environments, but forbidden in commands? In my understanding digits delimit command names (inherited from plain TeX), but why doesn't that restriction apply to environments? Wouldn't it have been more consistent to forbid digits in environment names as well?
macros environments
asked Apr 5 at 22:32
U. WindlU. Windl
1718
You actually can use numbers in commands. If you doexpandafterdefcsname mycommandwithanumber123456endcsname{}you'll define a commandmycommandwithanumber123456. The environments are created using thecsname...endcsnamepair, so it's fine.
– Phelype Oleinik
Apr 5 at 22:36
expandafterdefcsname macro2endcsname{command output}is valid syntax. You then must use it viacsname macro2endcsname.
– Steven B. Segletes
Apr 5 at 22:36
So the answer is "There are not forbidden, but they have to be used in a special way. Still it's recommended not to use them."?
– U. Windl
Apr 5 at 22:41
add a comment |
Finding out that I can have an environment named env2, but no command cmd2, I read Why are some characters not allowed in command sequences, but still I wonder:
Why are digits allowed in environments, but forbidden in commands? In my understanding digits delimit command names (inherited from plain TeX), but why doesn't that restriction apply to environments? Wouldn't it have been more consistent to forbid digits in environment names as well?
macros environments
asked Apr 5 at 22:32
U. WindlU. Windl
1718
Finding out that I can have an environment named env2, but no command cmd2, I read Why are some characters not allowed in command sequences, but still I wonder:
Why are digits allowed in environments, but forbidden in commands? In my understanding digits delimit command names (inherited from plain TeX), but why doesn't that restriction apply to environments? Wouldn't it have been more consistent to forbid digits in environment names as well?
macros environments
macros environments
asked Apr 5 at 22:32
U. WindlU. Windl
1718
asked Apr 5 at 22:32
U. WindlU. Windl
1718
asked Apr 5 at 22:32
U. WindlU. Windl
1718
asked Apr 5 at 22:32
U. WindlU. Windl
1718
asked Apr 5 at 22:32
U. WindlU. Windl
1718
1718
You actually can use numbers in commands. If you doexpandafterdefcsname mycommandwithanumber123456endcsname{}you'll define a commandmycommandwithanumber123456. The environments are created using thecsname...endcsnamepair, so it's fine.
– Phelype Oleinik
Apr 5 at 22:36
expandafterdefcsname macro2endcsname{command output}is valid syntax. You then must use it viacsname macro2endcsname.
– Steven B. Segletes
Apr 5 at 22:36
So the answer is "There are not forbidden, but they have to be used in a special way. Still it's recommended not to use them."?
– U. Windl
Apr 5 at 22:41
add a comment |
You actually can use numbers in commands. If you doexpandafterdefcsname mycommandwithanumber123456endcsname{}you'll define a commandmycommandwithanumber123456. The environments are created using thecsname...endcsnamepair, so it's fine.
– Phelype Oleinik
Apr 5 at 22:36
expandafterdefcsname macro2endcsname{command output}is valid syntax. You then must use it viacsname macro2endcsname.
– Steven B. Segletes
Apr 5 at 22:36
So the answer is "There are not forbidden, but they have to be used in a special way. Still it's recommended not to use them."?
– U. Windl
Apr 5 at 22:41
You actually can use numbers in commands. If you do
expandafterdefcsname mycommandwithanumber123456endcsname{} you'll define a command mycommandwithanumber123456. The environments are created using the csname...endcsname pair, so it's fine.– Phelype Oleinik
Apr 5 at 22:36
You actually can use numbers in commands. If you do
expandafterdefcsname mycommandwithanumber123456endcsname{} you'll define a command mycommandwithanumber123456. The environments are created using the csname...endcsname pair, so it's fine.– Phelype Oleinik
Apr 5 at 22:36
expandafterdefcsname macro2endcsname{command output} is valid syntax. You then must use it via csname macro2endcsname.– Steven B. Segletes
Apr 5 at 22:36
expandafterdefcsname macro2endcsname{command output} is valid syntax. You then must use it via csname macro2endcsname.– Steven B. Segletes
Apr 5 at 22:36
So the answer is "There are not forbidden, but they have to be used in a special way. Still it's recommended not to use them."?
– U. Windl
Apr 5 at 22:41
So the answer is "There are not forbidden, but they have to be used in a special way. Still it's recommended not to use them."?
– U. Windl
Apr 5 at 22:41
add a comment |
1 Answer
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The restriction is in the scanner, tex's "eyes" in the texbook terminology. Any sequence of characters may be used as a command name, however after a character of catcode 0 (normally ) then tex scans the next non-letter (character of catcode other than 11) or a contiguous sequence of letters, and tokenizes it as a single csname token.
This means that foo123 normally parses as the token foo followed by the three tokens 1, 2, 3. Unless you make digits catcode 11. Similarly section* is normally the token section followed by the token *.
environment names use do not require to parse the name via the escape character, (they use the csname primitive but that's an implementation detail so begin{tabular} accesses tabular but begin{tabular*} accesses the command with name tabular* (not the two tokens that would normally be generated by parsing tabular*).
So technically it would be quite hard to not allow digits (or other characters) in environment names, especially when latex was designed there was not the memory available to add that kind of character-by-character check.
edited Apr 5 at 23:24
Phelype Oleinik
25.1k54690
answered Apr 5 at 23:19
David CarlisleDavid Carlisle
499k4111451894
add a comment |
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1 Answer
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1 Answer
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active
oldest
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oldest
votes
The restriction is in the scanner, tex's "eyes" in the texbook terminology. Any sequence of characters may be used as a command name, however after a character of catcode 0 (normally ) then tex scans the next non-letter (character of catcode other than 11) or a contiguous sequence of letters, and tokenizes it as a single csname token.
This means that foo123 normally parses as the token foo followed by the three tokens 1, 2, 3. Unless you make digits catcode 11. Similarly section* is normally the token section followed by the token *.
environment names use do not require to parse the name via the escape character, (they use the csname primitive but that's an implementation detail so begin{tabular} accesses tabular but begin{tabular*} accesses the command with name tabular* (not the two tokens that would normally be generated by parsing tabular*).
So technically it would be quite hard to not allow digits (or other characters) in environment names, especially when latex was designed there was not the memory available to add that kind of character-by-character check.
edited Apr 5 at 23:24
Phelype Oleinik
25.1k54690
answered Apr 5 at 23:19
David CarlisleDavid Carlisle
499k4111451894
add a comment |
The restriction is in the scanner, tex's "eyes" in the texbook terminology. Any sequence of characters may be used as a command name, however after a character of catcode 0 (normally ) then tex scans the next non-letter (character of catcode other than 11) or a contiguous sequence of letters, and tokenizes it as a single csname token.
This means that foo123 normally parses as the token foo followed by the three tokens 1, 2, 3. Unless you make digits catcode 11. Similarly section* is normally the token section followed by the token *.
environment names use do not require to parse the name via the escape character, (they use the csname primitive but that's an implementation detail so begin{tabular} accesses tabular but begin{tabular*} accesses the command with name tabular* (not the two tokens that would normally be generated by parsing tabular*).
So technically it would be quite hard to not allow digits (or other characters) in environment names, especially when latex was designed there was not the memory available to add that kind of character-by-character check.
edited Apr 5 at 23:24
Phelype Oleinik
25.1k54690
answered Apr 5 at 23:19
David CarlisleDavid Carlisle
499k4111451894
add a comment |
The restriction is in the scanner, tex's "eyes" in the texbook terminology. Any sequence of characters may be used as a command name, however after a character of catcode 0 (normally ) then tex scans the next non-letter (character of catcode other than 11) or a contiguous sequence of letters, and tokenizes it as a single csname token.
This means that foo123 normally parses as the token foo followed by the three tokens 1, 2, 3. Unless you make digits catcode 11. Similarly section* is normally the token section followed by the token *.
environment names use do not require to parse the name via the escape character, (they use the csname primitive but that's an implementation detail so begin{tabular} accesses tabular but begin{tabular*} accesses the command with name tabular* (not the two tokens that would normally be generated by parsing tabular*).
So technically it would be quite hard to not allow digits (or other characters) in environment names, especially when latex was designed there was not the memory available to add that kind of character-by-character check.
edited Apr 5 at 23:24
Phelype Oleinik
25.1k54690
answered Apr 5 at 23:19
David CarlisleDavid Carlisle
499k4111451894
The restriction is in the scanner, tex's "eyes" in the texbook terminology. Any sequence of characters may be used as a command name, however after a character of catcode 0 (normally ) then tex scans the next non-letter (character of catcode other than 11) or a contiguous sequence of letters, and tokenizes it as a single csname token.
This means that foo123 normally parses as the token foo followed by the three tokens 1, 2, 3. Unless you make digits catcode 11. Similarly section* is normally the token section followed by the token *.
environment names use do not require to parse the name via the escape character, (they use the csname primitive but that's an implementation detail so begin{tabular} accesses tabular but begin{tabular*} accesses the command with name tabular* (not the two tokens that would normally be generated by parsing tabular*).
So technically it would be quite hard to not allow digits (or other characters) in environment names, especially when latex was designed there was not the memory available to add that kind of character-by-character check.
edited Apr 5 at 23:24
Phelype Oleinik
25.1k54690
answered Apr 5 at 23:19
David CarlisleDavid Carlisle
499k4111451894
edited Apr 5 at 23:24
Phelype Oleinik
25.1k54690
edited Apr 5 at 23:24
Phelype Oleinik
25.1k54690
edited Apr 5 at 23:24
Phelype Oleinik
25.1k54690
25.1k54690
answered Apr 5 at 23:19
David CarlisleDavid Carlisle
499k4111451894
answered Apr 5 at 23:19
David CarlisleDavid Carlisle
499k4111451894
answered Apr 5 at 23:19
David CarlisleDavid Carlisle
499k4111451894
499k4111451894
add a comment |
add a comment |
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You actually can use numbers in commands. If you do
expandafterdefcsname mycommandwithanumber123456endcsname{}you'll define a commandmycommandwithanumber123456. The environments are created using thecsname...endcsnamepair, so it's fine.– Phelype Oleinik
Apr 5 at 22:36
expandafterdefcsname macro2endcsname{command output}is valid syntax. You then must use it viacsname macro2endcsname.– Steven B. Segletes
Apr 5 at 22:36
So the answer is "There are not forbidden, but they have to be used in a special way. Still it's recommended not to use them."?
– U. Windl
Apr 5 at 22:41