Nehtdx

Approximately how much travel time was saved by the opening of the Suez Canal in 1869?

What typically incentivizes a professor to change jobs to a lower ranking university?

Why can't we play rap on piano?

How much RAM could one put in a typical 80386 setup?

Languages that we cannot (dis)prove to be Context-Free

Malformed Address '10.10.21.08/24', must be X.X.X.X/NN or

How to determine what difficulty is right for the game?

Roll the carpet

How is it possible to have an ability score that is less than 3?

Arrow those variables!

Watching something be written to a file live with tail

A newer friend of my brother's gave him a load of baseball cards that are supposedly extremely valuable. Is this a scam?

Horror movie about a virus at the prom; beginning and end are stylized as a cartoon

Maximum likelihood parameters deviate from posterior distributions

High voltage LED indicator 40-1000 VDC without additional power supply

Replacing matching entries in one column of a file by another column from a different file

Client team has low performances and low technical skills: we always fix their work and now they stop collaborate with us. How to solve?

How to move a thin line with the black arrow in Illustrator?

Could an aircraft fly or hover using only jets of compressed air?

What defenses are there against being summoned by the Gate spell?

Can a Cauchy sequence converge for one metric while not converging for another?

Perform and show arithmetic with LuaLaTeX

What is a clear way to write a bar that has an extra beat?

Are astronomers waiting to see something in an image from a gravitational lens that they've already seen in an adjacent image?

LaTeX: Why are digits allowed in environments, but forbidden in commands?

What exactly do csname and endcsname do?Why are some characters not allowed in command sequencesWhy does LaTeX make a distinction between commands and environments?Do all starred commands have anything in common?Why are some characters not allowed in command sequencesSuggestions for an automatic taxonomy environmentUse a character other than the backslash for commandsWhy are LaTeX macros so inconsistent?Are end… macro names reserved in LaTeX2e?Can't use command with square brackets in matrix environmentHow to control conditional statements within new commands and environmentsCreating Commands which Make New Environments

1

1

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

share|improve this question

asked 2 hours ago

U. WindlU. Windl

1547

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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 macro2endcsnamecommand 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
  

  
  
  
  

add a comment | 

1

1

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

share|improve this question

asked 2 hours ago

U. WindlU. Windl

1547

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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 macro2endcsnamecommand 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
  

  
  
  
  

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

share|improve this question

asked 2 hours ago

U. WindlU. Windl

1547

share|improve this question

asked 2 hours ago

U. WindlU. Windl

1547

share|improve this question

asked 2 hours ago

U. WindlU. Windl

1547

asked 2 hours ago

U. WindlU. Windl

1547

asked 2 hours ago

U. WindlU. Windl

1547

1 Answer
1

active

oldest

votes

4

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 begintabular accesses tabular but begintabular* 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.

share|improve this answer

edited 1 hour ago

Phelype Oleinik

24.9k54690

answered 1 hour ago

David CarlisleDavid Carlisle

497k4111441891

add a comment | 

Your Answer

StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "85"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);

else
createEditor();

);

function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);



);

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2ftex.stackexchange.com%2fquestions%2f483440%2flatex-why-are-digits-allowed-in-environments-but-forbidden-in-commands%23new-answer', 'question_page');

);

Post as a guest

Name

Email

Required, but never shown

4

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 begintabular accesses tabular but begintabular* 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.

share|improve this answer

edited 1 hour ago

Phelype Oleinik

24.9k54690

answered 1 hour ago

David CarlisleDavid Carlisle

497k4111441891

add a comment | 

4

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 begintabular accesses tabular but begintabular* 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.

share|improve this answer

edited 1 hour ago

Phelype Oleinik

24.9k54690

answered 1 hour 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 begintabular accesses tabular but begintabular* 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.

share|improve this answer

edited 1 hour ago

Phelype Oleinik

24.9k54690

answered 1 hour ago

David CarlisleDavid Carlisle

497k4111441891

share|improve this answer

edited 1 hour ago

Phelype Oleinik

24.9k54690

answered 1 hour ago

David CarlisleDavid Carlisle

497k4111441891

edited 1 hour ago

Phelype Oleinik

24.9k54690

edited 1 hour ago

Phelype Oleinik

24.9k54690

answered 1 hour ago

David CarlisleDavid Carlisle

497k4111441891

answered 1 hour ago

David CarlisleDavid Carlisle

497k4111441891