gnatprep ¶The input text contains preprocessor conditional inclusion lines as well as general symbol substitution sequences.
Preprocessor conditional inclusion commands have the form:
#if <expression> [then] lines #elsif <expression> [then] lines #elsif <expression> [then] lines ... #else lines #end if;
In this example, <expression> is defined by the following grammar:
<expression> ::= <symbol> <expression> ::= <symbol> = "<value>" <expression> ::= <symbol> = <symbol> <expression> ::= <symbol> = <integer> <expression> ::= <symbol> > <integer> <expression> ::= <symbol> >= <integer> <expression> ::= <symbol> < <integer> <expression> ::= <symbol> <= <integer> <expression> ::= <symbol> 'Defined <expression> ::= not <expression> <expression> ::= <expression> and <expression> <expression> ::= <expression> or <expression> <expression> ::= <expression> and then <expression> <expression> ::= <expression> or else <expression> <expression> ::= ( <expression> )
For the first test, (<expression> ::= <symbol>), the symbol must have
either the value true or false. The right-hand of the
symbol definition must be one of the (case-insensitive) literals
True or False. If the value is true, the
corresponding lines are included and if the value is false, they are
excluded.
When comparing a symbol to an integer, the integer is any non negative literal integer as defined in the Ada Reference Manual, such as 3, 16#FF# or 2#11#. The symbol value must also be a non negative integer. Integer values in the range 0 .. 2**31-1 are supported.
The test (<expression> ::= <symbol>’Defined) is true only if
the symbol has been defined in the definition file or by a -D
switch on the command line. Otherwise, the test is false.
The equality tests are case insensitive, as are all the preprocessor lines.
If the symbol referenced is not defined in the symbol definitions
file, the result depends on whether or not you have specified the
-u switch. If you have, the symbol is treated as if it had
the value false and the test fails. If not,
it’s an error to reference an undefined symbol. It’s also an
error to reference a symbol that you have defined with a value other than
True or False.
The use of the not operator inverts the sense of this logical
test. You can’t combine the not operator with the or or
and operators without parentheses. For example, you can’t write
“if not X or Y then” allowed, but can write either “if (not X) or Y
then” or “if not (X or Y) then”.
The then keyword is optional, as shown.
You must place the # in the first non-blank character on a line,
i.e., it must be preceded only by spaces or horizontal tabs, but
otherwise the format is free form. You may place spaces or tabs
between the # and the keyword. The keywords and the symbols are
case insensitive, as in normal Ada code. You can write comments on a
preprocessor line, but other than that, you can’t place any other
tokens on a preprocessor line. You can have any number of elsif
clauses, including none at all. The else is optional, as in Ada.
You obtain symbol substitution outside of preprocessor lines by using the sequence:
$symbol
anywhere within a source line, except in a comment or within a
string literal. The identifier
following the $ must match one of the symbols defined in the symbol
definition file and the resulting output substitutes the value of the
symbol in place of $symbol in the output file.
Note that although you can’t substitute strings within a string
literal, you can have a symbol whose defined value is a string
literal. So instead of setting XYZ to hello and writing:
Header : String := "$XYZ";
you should set XYZ to "hello" and write:
Header : String := $XYZ;
and then the substitution will occur as desired.