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 2 hours ago
U. WindlU. Windl
1597
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 2 hours ago
U. WindlU. Windl
1597
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
2 hours ago
expandafterdefcsname macro2endcsname{command output}is valid syntax. You then must use it viacsname macro2endcsname.
– Steven B. Segletes
2 hours ago
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
2 hours ago
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 2 hours ago
U. WindlU. Windl
1597
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 2 hours ago
U. WindlU. Windl
1597
asked 2 hours ago
U. WindlU. Windl
1597
asked 2 hours ago
U. WindlU. Windl
1597
asked 2 hours ago
U. WindlU. Windl
1597
asked 2 hours ago
U. WindlU. Windl
1597
1597
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
2 hours ago
expandafterdefcsname macro2endcsname{command output}is valid syntax. You then must use it viacsname macro2endcsname.
– Steven B. Segletes
2 hours ago
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
2 hours ago
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
2 hours ago
expandafterdefcsname macro2endcsname{command output}is valid syntax. You then must use it viacsname macro2endcsname.
– Steven B. Segletes
2 hours ago
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
2 hours ago
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
2 hours ago
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
2 hours ago
expandafterdefcsname macro2endcsname{command output} is valid syntax. You then must use it via csname macro2endcsname.– Steven B. Segletes
2 hours ago
expandafterdefcsname macro2endcsname{command output} is valid syntax. You then must use it via csname macro2endcsname.– Steven B. Segletes
2 hours ago
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
2 hours ago
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
2 hours ago
add a comment |
1 Answer
1
active
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 2 hours ago
Phelype Oleinik
24.9k54690
answered 2 hours ago
David CarlisleDavid Carlisle
497k4111441891
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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votes
active
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 2 hours ago
Phelype Oleinik
24.9k54690
answered 2 hours ago
David CarlisleDavid Carlisle
497k4111441891
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 2 hours ago
Phelype Oleinik
24.9k54690
answered 2 hours ago
David CarlisleDavid Carlisle
497k4111441891
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 2 hours ago
Phelype Oleinik
24.9k54690
answered 2 hours ago
David CarlisleDavid Carlisle
497k4111441891
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 2 hours ago
Phelype Oleinik
24.9k54690
answered 2 hours ago
David CarlisleDavid Carlisle
497k4111441891
edited 2 hours ago
Phelype Oleinik
24.9k54690
edited 2 hours ago
Phelype Oleinik
24.9k54690
edited 2 hours ago
Phelype Oleinik
24.9k54690
24.9k54690
answered 2 hours ago
David CarlisleDavid Carlisle
497k4111441891
answered 2 hours ago
David CarlisleDavid Carlisle
497k4111441891
answered 2 hours ago
David CarlisleDavid Carlisle
497k4111441891
497k4111441891
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
2 hours ago
expandafterdefcsname macro2endcsname{command output}is valid syntax. You then must use it viacsname macro2endcsname.– Steven B. Segletes
2 hours ago
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
2 hours ago