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4 Lexical Syntax

The lexical syntax for identifiers used for sorts, operation symbols, and variables is as follows, using conventional notation for character classes in the productions for WORD and SIGNS.

  ID               ::= MIX-ID  |  MIX-ID [ ID,...,ID ]
  MIX-ID           ::= TOKEN  |  TOKEN __  |  __  
                     | TOKEN __ MIX-ID  |  __ MIX-ID
  TOKEN-ID         ::= TOKEN  |  TOKEN [ ID,...,ID ]
  SIMPLE-ID        ::= WORDS

  TOKEN            ::= WORDS  |  SIGNS  |  .WORDS
  WORDS            ::= WORD_..._WORD 
  WORD             ::= [A-Za-z0-9'À-ÖØ-öø-ÿ]+ 
  SIGNS            ::= [+-*/&^#$~>=<@?!|\\:.{}\[\]!`-?`×÷]+ 

! VERSION           ::= ... (not yet decided)

The following characters are not allowed to occur at all in a TOKEN:

                        (  )  ;  ,  `  "  %

The following restrictions are not captured by the grammar above:

Occurrences of `{...}' and of `[...]' in an ID must be balanced. E.g., `{[__}]' and `{__]' are not allowed.
No keyword is ever recognized as a complete TOKEN.
They may however be used together with other words in a complete WORDS sequence, or as part of a single WORD.
The ISO Latin-1 characters for product `×', negation `¬', and raised dot `·' are recognized as alternatives for the terminal symbols that get displayed that way: `*', `not', and `.', respectively.
None of the following sequences of characters is recognized as a complete TOKEN (since they all have to be recognized as terminal symbols):
```
      :  :?  ::=  =  =>  <=>  .  ·  |  |->  \/  /\   ¬  {  }  [  ]
```
They may however be used together with other characters in a complete TOKEN. E.g., `==', `:=', `||', `{|' are all recognized as complete TOKENs. The single characters `<', `*', `?', `!', and `/' are also recognized as complete TOKENs, despite their use elsewhere as terminal symbols.
It is assumed that white space always terminates a lexical symbol. The next lexical symbol recognized is as long as possible.

See Section 6 for the proposed lexical syntax of comments and annotations.

CoFI Document: CASL/SyntaxIssues --Version 0.99-- 17 February 1998.
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