5. Identifiers

The names given to variables, functions, and data types are called identifiers. There are some restrictions upon the actual characters that make up an identifier. An identifier name must start with a letter ([A-Za-z]), an underscore character, or a dollar sign. The rest of the characters in the name can be any combination of letters, digits, dollar signs, or underscore characters. However, all identifiers whose name begins with two underscore characters are reserved for internal use by the interpreter and declarations of objects with such names should be avoided.

Examples of valid identifiers include:

      mary    _3    _this_is_ok
      a7e1    $44   _44$_Three

      7abc   2e0    #xx

Although the maximum length of identifiers is unspecified by the language, the length should be kept below 64 characters.

The following identifiers are reserved by the language for use as keywords:

       !if           _for        define    loop    shl      variable
       ERROR_BLOCK   abs         do        mod     shr      while
       EXIT_BLOCK    and         do_while  mul2    sign     xor
       USER_BLOCK0   andelse     else      not     sqr
       USER_BLOCK1   break       exch      or      static
       USER_BLOCK2   case        for       orelse  struct
       USER_BLOCK3   chs         forever   pop     switch
       USER_BLOCK4   continue    if        return  typedef