Improve so that .13 is a floating point number, (#2491)

Closes #2122
* Improve so that .13 is a floating point number, and some minor corrections.
* Introduce UNSIGNED-REAL and UNSIGNED-NUMBER to be able say that 13 is not a floating point, but can still be used everywhere where numbers are expected (13. is a floating point number).
* Add more examples
* Simplify descriptive text as proposed with good link to grammar

chapters/lexicalstructure.tex

@@ -135,10 +135,10 @@ \section{Literal Constants}\doublelabel{literal-constants}
 \subsection{Floating Point Numbers}\doublelabel{floating-point-numbers}
 
 A floating point number is expressed as a decimal number in the form of
-a sequence of decimal digits optionally followed by a decimal point,
-optionally followed by an exponent. At least one digit must be present.
-The exponent is indicated by an E or e, followed by an optional sign (+
-or -) and one or more decimal digits. The minimal recommended range is
+a sequence of decimal digits followed by a decimal point, followed by decimal digits,
+followed by an exponent indicated by E or e followed by a sign
+and one or more decimal digits. The various parts can be omitted, see \lstinline!UNSIGNED_REAL! in~\autoref{lexical-conventions} for
+details and also the examples below. The minimal recommended range is
 that of IEEE double precision floating point numbers, for which the
 largest representable positive number is 1.7976931348623157E+308 and the
 smallest positive number is 2.2250738585072014E-308. For example, the
@@ -152,15 +152,18 @@ \subsection{Floating Point Numbers}\doublelabel{floating-point-numbers}
 For example, all of the following literals denote the same number:
 
 \begin{lstlisting}[language=modelica]
-13., 13E0, 1.3e1, 0.13E2
+13., 13E0, 1.3e1, 0.13E2, .13E2
 \end{lstlisting}
+The last variant shows that that the leading zero is optional (in that case decimal digits must be present).
+Note that \lstinline!13! is not in this list, since it is not a floating point number,
+but can be converted to a floating point number.
 
 \subsection{Integer Literals}\doublelabel{integer-literals}
 
 Literals of type \lstinline!Integer! are sequences of decimal digits, e.g. as in the
-integer numbers \lstinline!33, 0, 100, 30030044!. {[}\emph{Negative numbers are
+integer numbers \lstinline!33!, \lstinline!0!, \lstinline!100!, \lstinline!30030044!. {[}\emph{Negative numbers are
 formed by unary minus followed by an integer literal}{]}. The minimal
-recommended number range is from -2147483648 to +2147483647 for a
+recommended number range is from -2147483648 to +2147483647 corresponding to a
 two's-complement 32-bit integer implementation.
 
 \subsection{Boolean Literals}\doublelabel{boolean-literals}

chapters/syntax.tex

@@ -26,22 +26,24 @@ \section{Lexical conventions}\doublelabel{lexical-conventions}
          "\a" | "\b" | "\f" | "\n" | "\r" | "\t" | "\v"
 DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
 UNSIGNED-INTEGER = DIGIT { DIGIT }
-UNSIGNED-NUMBER = UNSIGNED-INTEGER [ "." [ UNSIGNED-INTEGER ] ]
-        [ ( "e" | "E" ) [ "+" | "-" ] UNSIGNED-INTEGER ]
+UNSIGNED-REAL = UNSIGNED-INTEGER  "." [ UNSIGNED-INTEGER ]
+     |  UNSIGNED_INTEGER [ "." [ UNSIGNED_INTEGER ] ] ( "e" | "E" ) [ "+" | "-" ] UNSIGNED-INTEGER
+     |   "."  UNSIGNED-INTEGER [ ( "e" | "E" ) [ "+" | "-" ] UNSIGNED-INTEGER ]
 \end{lstlisting}
 \textrm{S-CHAR} is any member of the Unicode character set
 (\url{http://www.unicode.org}; see \autoref{mapping-package-class-structures-to-a-hierarchical-file-system} for storing as UTF-8 on files) except double-quote """, and backslash "\textbackslash{}"
 
-For identifiers the redundant escapes (\lstinline!'\?' and '\"'!) are the same as the corresponding non-escaped
-variants (\lstinline!'?' and '"'!). {[}\emph{The single quotes are part of an
+For identifiers the redundant escapes (\lstinline!'\?'! and \lstinline!'\"'!) are the same as the corresponding non-escaped
+variants (\lstinline!'?'! and \lstinline!'"'!). {[}\emph{The single quotes are part of an
 identifier. E.g. 'x' and x are different IDENTs}{]}.
 
 Note:
 
 \begin{itemize}
 \item
   Whitespace and comments can be used between separate lexical units
-  and/or symbols, and also separates them. Whitespace and comments
+  and/or symbols, and also separates them. Each lexical unit will consume the maximum number of characters from the input stream.
+  Whitespace and comments
   cannot be used inside other lexical units, except for STRING and
   Q-IDENT where they are treated as part of the STRING or Q-IDENT
   lexical unit.
@@ -364,6 +366,8 @@ \subsection{Expressions}\doublelabel{expressions1}
    | "{" array-arguments "}"
    | end
 
+UNSIGNED-NUMBER : UNSIGNED-INTEGER | UNSIGNED-REAL
+
 type-specifier : ["."] name
 
 name : IDENT { "." IDENT }