Mailfromd
	General-Purpose Mail Filter	Sergey Poznyakoff

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4.7.1 Built-in constants

Several constants are built into the MFL compiler. To discern them from user-defined ones, their names start and end with two underscores (‘__’).

The following constants are defined in mailfromd version 6.0:

Built-in constant: string __file__

Expands to the name of the current source file.

Built-in constant: string __function__

Expands to the name of the current lexical context, i.e. the function or handler name.

Built-in constant: number __line__

Expands to the current line number in the input source file.

Built-in constant: number __major__

Expands to the major version number.

The following example uses __major__ constant to determine if some version-dependent feature can be used:

if __major__ > 2 # Use some version-specific feature fi

Built-in constant: number __minor__

Expands to the minor version number.

Built-in constant: string __module__

Expands to the name of the current module (see section Modules).

Built-in constant: string __package__

Expands to the package name (‘mailfromd’)

Built-in constant: number __patch__

For alpha versions and maintenance releases expands to the version patch level. For stable versions, expands to ‘0’.

Built-in constant: string __defpreproc__

Expands to the default external preprocessor command line, if the preprocessor is used, or to an empty string if it is not, e.g.:

__defpreproc__ ⇒ "/usr/bin/m4 -s"

See section MFL Preprocessor, for information on preprocessor and its features.

Built-in constant: string __preproc__

Expands to the current external preprocessor command line, if the preprocessor is used, or to an empty string if it is not. Notice, that it equals __defpreproc__, unless the preprocessor was redefined using ‘--preprocessor’ command line option (see section –preprocessor).

Built-in constant: string __version__

Expands to the textual representation of the program version (e.g. ‘3.0.90’)

Built-in constant: string __defstatedir__

Expands to the default state directory (see statedir).

Built-in constant: string __statedir__

Expands to the current value of the program state directory (see statedir). Notice, that it is the same as __defstatedir__ unless the state directory was redefined at run time.

Built-in constants can be used as variables, this allows to expand them within strings or here-documents. The following example illustrates the common practice used for debugging configuration scripts:

func foo(number x)
do
  echo "%__file__:%__line__: foo called with arg %x"
  …
done

If the function foo were called in line 28 of the script file /etc/mailfromd.mf, like this: foo(10), you will see the following string in your logs:

/etc/mailfromd.mf:28: foo called with arg 10

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