Yodl builtin functions(7)

NAME
yodlbuiltins - Builtins for the Yodl converters

SYNOPSIS
This manual page lists the standard builtins of the Yodl package.

DESCRIPTION
The following list shows the builtins defined by the Yodl converters define and which can be used in Yodl documents. Refer to the Yodl user guide, distributed with the Yodl package, for a full description.

The following list shows all builtins of the package in alphabetical order.

NOTE: Starting with Yodl version 3.00.0 Yodl’s default file inclusion behavior has changed. The current working directory no longer remains fixed at the directory in which Yodl is called, but is volatile, changing to the directory in which a yodl-file is located. This has the advantage that Yodl’s file inclusion behavior now matches the way C’s #include directive operates; it has the disadvantage that it may break some current documents. Conversion, however is simple but can be avoided altogether if Yodl’s -L (--legacy-include) option is used. The builtins INCLUDEFILE, NOEXPANDINCLUDE and NOEXPANDPATHINCLUDE are affected by this new behavior.

Yodl’s builtin commands
    As mentioned previously, YODL’s input consists of text and of commands. YODL supports a number of built-in commands which may either be used in a YODL document, or which can be used to create a macro package.

    Don’t despair if you find that the description of this section is too technical. Exactly for this reason, YODL supports the macro packages to make the life of a documentation writer easier. E.g., see chapter [MACROPACKAGE] that describes a macro package for YODL.

    Most built-in functions and macros expand the information they receive the way they receive the information. I.e., the information itself is only evaluated by the time it is eventually inserted into an output medium (usually a file). However, some builtin functions will evaluate their argument(s) once the argument is processed. They are:

o   The ERROR() built-in function (see section [ERROR]);

o   The EVAL() built-in function (see section [EVAL]);

o   The FPUTS() built-in function (see section [FPUTS]);

o   The INTERNALINDEX() built-in function (see section [INTERNALINDEX]);

o   The TYPEOUT() built-in function (see section [TYPEOUT]);

o   The UPPERCASE() built-in function (see section [UPPERCASE]);

o   The WARNING() built-in function (see section [WARNING]); All other built-in functions will not evaluate their arguments. See the mentioned functions for details, and in particular EVAL() for a description of this evaluation process.

ADDTOCOUNTER
    The ADDTOCOUNTER function adds a given value to a counter. It expects two parameter lists: the counter name, and the value to add. The counter must be previously created with DEFINECOUNTER.

    The value to add can be negative; in that case, a value is of course subtracted from the counter.

    See further section [COUNTERS].

ADDTOSYMBOL
    Since Yodl version 2.00 symbols can be manipulated. To add text to an existing symbol the builtin ADDTOSYMBOL is available. It expects two parameter lists: the symbol’s name, and the text to add to the symbol. The symbol must have been created earlier using DEFINECOUNTER (see section [DEFINECOUNTER]). The macro’s second argument is not evaluated while ADDTOSYMBOL is processed. Therefore, it is easy to add the text of another symbol or the expansion of a macro to a symbol value. E.g.,
        ADDTOSYMBOL(one)(SYMBOLVALUE(two)XXnl())

    This will add the text of symbol two, followed by a new line, to the contents of symbol one only when symbol one is evaluated, not when ADDTOSYMBOL is evaluated.

    Example:
        ADDTOSYMBOL(LOCATION)(this is appended to LOCATION)

ATEXIT
    ATEXIT takes one parameter list as argument. The text of the parameter list is appended to the output file. Note that this text is subject to character table translations etc..

    An example using this function is the following. A document in the LaTeX typesetting language requires \end{document} to occur at the end of the document. To automatically append this string to the output file, the following specification can be used:
        ATEXIT(NOEXPAND(\end{document}))

    Several ATEXIT lists can be defined. They are appended to the output file in the reverse order of specification; i.e., the first ATEXIT list is appended to the output file last. That means that in general the ATEXIT text should be specified when a `matching’ starting command is sent to the output file; as in:
        COMMENT(Start the LaTeX document.)
        NOEXPAND(\begin{document})

        COMMENT(Ensure its proper ending.)
        ATEXIT(NOEXPAND(\end{document}))

CHAR
    The command CHAR takes one argument, a number or a character, and outputs its corresponding ASCII character to the final output file. This command is built for `emergency situations’, where you need to typeset a character despite the fact that it may be redefined in the current character table (for a discussion of character tables, see [CHARTABLES]). Also, the CHAR function can be used to circumvent Yodl’s way of matching parentheses in a parameter list.

    The following arguments may be specified with CHAR (attempted in this order):

o   A decimal number indicating the number of the character in the ascii-table (for example CHAR(41));

o   A plain, single character (for example CHAR(#)).

    So, when you’re sure that you want to send a printable character that is not a closing parenthesis to the output file, you can use the form CHAR(c), c being the character (as in, CHAR(;)). To send a non-printable character or a closing parenthesis to the output file, look up the ASCII number of the character, and supply that number as argument to the CHAR command.

    Example: The following two statements send an A to the output file.
        CHAR(65)
        CHAR(A)

    The following statement sends a closing parenthesis:
        CHAR(41)

    Another way to send a string to the output file without expansion by character tables or by macro interpretation, is by using the function NOTRANS (see section [NOTRANS]). If you want to send a string to the output without macro interpretation, but with character table translation, use NOEXPAND (see section [NOEXPAND]).

CHDIR
    The command CHDIR takes one argument, a directory to change to. This command is implemented to simplify the working with includefile (see includefile in yodlmacros(7)). As a demonstration, consider the following fragment:
        includefile(subdir/onefile)
        includefile(subdir/anotherfile)
        includefile(subdir/yetanotherfile)

    This fragment can be changed to:
        CHDIR(subdir)
        includefile(onefile)
        includefile(anotherfile)
        includefile(yetanotherfile)
        CHDIR(..)

    The current directory, as given to CHDIR, only affects how includefile will search for its files.

    Note that this example assumes that the current working directory is a member of Yodl’s include-path specification (cf., Yodl’s --include option).

COMMENT
    The COMMENT function takes one parameter list. The text in the list is treated as comment. I.e., it is ignored. The text is not copied to the final output file.

COUNTERVALUE
    COUNTERVALUE expands to the value of a counter. Its single parameter list must contain the name of a counter. The counter must have been created earlier using the builtin DEFINECOUNTER.
    Example:
        The counter has value COUNTERVALUE(MYCOUNTER).

    See also section [COUNTERS].

DECWSLEVEL
    DECWSLEVEL requires one (empty) parameter list. It reduces the current white-space level. The white-space level typically is used in files that only define Yodl macros. When no output should be generated while processing these files, the white-space level can be used to check for this. If the white-space level exceeds zero, a warning will be generated if the file produces non-whitespace output. The builtin function DECWSLEVEL is used to reduce the whitespace level following a previous call of INCWSLEVEL.

    Once the white space level exceeds zero, no output will be generated. White space, therefore will effectively be ignored. The white space level cannot be reduced to negative values. A warning is issued if that would have happened if it were allowed.

    Example:
        INCWSLEVEL()
        DEFINESYMBOL(....)
        DEFINEMACRO(...)(...)(...)
        DECWSLEVEL()

    Without the INCWSLEVEL and DECWSLEVEL, calls, the above definition would generate four empty lines to the output stream.

    The INCWSLEVEL and DECWSLEVEL calls may be nested. The best approach is to put an INCWSLEVEL at the first line of a macro-defining Yodl-file, and a matching DECWSLEVEL call at the very last line.

DEFINECHARTABLE
    DEFINECHARTABLE is used to define a character translation table. The function expects two parameterlists, containing the name of the character table and character table translations on separate lines. These character table translations are of the form
        character = quoted-string

    Here, character is always a value within single quotes. It may be a single character, an octal character value or a hexadecimal character value. The single character may be prefixed by a \-character (e.g., ’\\’). The octal character value must start with a backslash, followed by three octal digits (e.g., ’\045’. The hexadecimal character value starts with 0x, followed by two hexadecimal characters. E.g., ’0xbe’. The double quoted string may contain anything (but the string must be on one line), possibly containing escape-sequences as well: in the double quoted string the standard C escape sequences \a (alert), \b (beep), \f (formfeed), \n (newline), \r (carriage return), \t (tab), and \v (vertical tab) are recognized and automatically converted to their special meanings. Starting with Yodl 2.14.0 octal and hexadecimal constants may also be used. E.g., character Y may also be specified using the octal value \131 or the hexadecimal value \x59. Any other character following a defines itself: \\ represents a single backslash character.

    Example:
        DEFINECHARTABLE(demotable)(
            ’&’     = "&amp;"
            ’\\’    = "\\backslash"
            ’\045’  = "oct(45)"
            ’0xa4’  = "hex(a4)"
        )

    The builtin function DEFINECHARTABLE does not activate the table. The table is merely defined. To activate the character translation table, use USECHARTABLE. The discussion of character tables is postponed to section [CHARTABLES].

DEFINECOUNTER
    DEFINECOUNTER creates a new counter, to be subsequently used by, e.g, the USECOUNTER function. DEFINECOUNTER expects two parameter list: the name of the counter to create and an optional initial value. By default the counter will be initialized to zero.

    Examples:
        DEFINECOUNTER(YEAR)(1950)
        DEFINECOUNTER(NTIMES)()

    See also section [COUNTERS].

DEFINEMACRO
    DEFINEMACRO is used to define new macros. This function requires three parameter lists:

o   An identifier, being the name of the macro to define. This identifier may only consist of uppercase or lowercase characters. Note that it can not contain numbers, nor underscore characters.

o   A number, stating the number of arguments that the macro will require once used. The number must be in the range 0 to 61.

o   The text that the macro will expand to, once used. This text may contain the strings ARGx, x being 1, 2, etc.. At these places the arguments to the macro will be pasted in. The numbers that identify the arguments are 1 to 9, then A to Z and finally a to z. This gives a range of 61 expandable arguments, which is enough for all real-life applications. For example, the following fragment defines a macro bookref, which can be used to typeset a reference to a book. It requires three arguments; say, an author, a title and the name of a publisher:
        DEFINEMACRO(bookref)(3)(
            Author(s):           ARG1
            Book title:          ARG2
            Published by:        ARG3
        )

    Such a macro could be used as follows:
        bookref(Sobotta/Becher)
               (Atlas der Anatomie des Menschen)
               (Urban und Schwarzenberg, Berlin, 1972)

    When called, it would produce the following output:
            Author(s):           Sobotta/Becher
            Book title:          Atlas der Anatomie des Menschen
            Published by:        Urban und Schwarzenberg, Berlin, 1972

    While applying a macro, the three parameter lists are pasted to the places where ARG1, ARG2 etc. occur in the definition.

    Note the following when defining new macros:

o   The parameter list containing the name of the new macro, (bookref) in the above example, must occur right after DEFINEMACRO. No spaces are allowed in between. Space characters and newlines may however occur following this first parameter list.

    This behavior of the yodl program is similar to the usage of the defined macro: the author information must, enclosed in parentheses, follow right after the bookref identifier. I implemented this feature to improve the distinguishing between macros and real text. E.g., a macro me might be defined, but the text
        I like me (but so do you)

    still is simple text; the macro me only is activated when a parenthesis immediately follows it.

o   Be careful when placing newlines or spaces in the definition of a new macro. E.g., the definition, as given:
        DEFINEMACRO(bookref)(3)(
            Author(s):           ARG1
            Book title:          ARG2
            Published by:        ARG3
        )

    introduces extra newlines at the beginning and ending of the macro, which will be copied to the output each time the macro is used. The extra newline occurs, of course, right before the sequence Author(s): and following the evaluation of ARG3. A simple backslash character at the end of the DEFINEMACRO line would prevent the insertion of extra newline characters:
        DEFINEMACRO(bookref)(3)(\
            Author(s):           ARG1
            Book title:          ARG2
            Published by:        ARG3
        )

o   Note that when a macro is used which requires no arguments at all, one empty parameter list still must be specified. E.g., my macro package (see chapter [MACROPACKAGE]) defines a macro it that starts a bullet item in a list. The macro takes no arguments, but still must be typed as it().

    This behavior is consistent: it helps distinguish which identifiers are macros and which are simple text.

o   Macro arguments may evaluate to text. When a \ is appended to the macro-argument, or in the default input handling within a non-zero white-space level (see section [INCWSLEVEL]) this may invalidate a subsequent macro call. E.g., the macro
        DEFINEMACRO(oops)(1)(
            ARG1
            XXnl()
        )

    will, when called as oops(hello world), produce the output:
        hello worldXXnl()

    To prevent this gluing to arguments to subsequent macros, a single + should be prepended to the macro call:
        DEFINEMACRO(oops)(1)(
            ARG1
            +XXnl()
        )

    See also section [PLUSIDENT] obout the `+identifier’-sequence.

o   Note the preferred layout of macro definitions and macro calls. Adhere to this form, to prevent drowning in too many parentheses. In particular:

o   Put all elements of the macro definition on one line, except for the macro-expansion itself. Each expansion element should be on a line by itself.

o   When calling macros put the macro parameter lists underneath each other. If the macrolists themselves contain macro-calls, put each call again on a line of its own, indenting one tab-position beyond the location of the opening parenthesis of the argument.

o   No continnuation backslashes are required between parameter lists. So, do not use them there to prevent unnecessary clutter.

o   With complex calls, indent just the arguments, and put the parentheses in their required of logical locations. Example of a complex call:
            complex(
                first(
                    ARG1
                )(
                    ARG2
                    +XXnl()
                )
                ARG3
                +nop()
                ARG4
                +XXnl()
            )

o   Macro expansion proceeds as follows:

o   The parameter lists are read from the input

o   The contents of the parameters then replace their ARGx references in the macro’s definition (in some exceptional cases, clearly indicated as such when applicable, the arguments will themselves be evaluated first, and then these evaluated arguments are used as replacements for their corresponding ARGx references).

o   The now modified macro is read by Yodl’s lexical scanner. This may result in yet another macro expansion, which will then be evaluated recursively.

o   Eventually, all expansion is completed (well, should complete, since Yodl doesn’t test for eternal recursion) and scanning of the input continues beyond the original macro call. For example, assume we have the following two macros:
        DEFINEMACRO(First)(1)(
            Hello ARG1
            +XXnl()
        )
        DEFINEMACRO(Second)(1)(
            First(ARG1)
            First(ARG1)
        )

    and the following call is issued:
        Second(Yodl)

    then the following will happen:

o   Second(Yodl) is read as encountered.

o   ARG1 in Second is replaced by YODL, and the resulting macro body is sent to the lexical scanner for evaluation: It will see:
        First(Yodl)First(Yodl)

o   The first call to First() is now evaluated. This will put (after replacing ARG1 by YODL) the following on the scanner’s input:
        Hello Yodl+XXnl()First(Yodl)

o   Hello Yodl contains no macro call, so it is written to the output stream. Remains:
        +XXnl()First(Yodl)

o   Assume XXnl() merely contains a newline (represented by \n, here), so +XXnl() is now replaced by \n. This results in the following input for the lexical scanner:
        \nFirst(Yodl)

o   The \n is now written to the output stream, and the scanner sees:
        First(Yodl)

o   The second call to First() is now evaluated. This will put the following on the scanner’s input:
        Hello Yodl+XXnl()

o   Hello Yodl is written to the output stream. Remains:
        +XXnl()

o   +XXnl() is now replaced by \n. The lexical scanner sees:
        \n

o   The newline is printed and we’re done.

DEFINESYMBOL
    NOTE: this function has changed at the release of Yodl 2.00. It now expects two parameter lists, rather than one

    DEFINESYMBOL expects two arguments. An identifier, which is the name of the symbol to define, and the textual value of the symbol. If the second argument is empty, the symbol is defined, but has an empty value.

    The earlier interpretation of a Yodl symbol as a logical flag can still be used, but allowing it to obtain textual values greatly simplifies various Yodl macros.

    Example:
        DEFINESYMBOL(Yodl)(Your own document language)
        DEFINESYMBOL(Options)()

DELETECHARTABLE
    DELETECHARTABLE removes a definition of a character table that was defined by DEFINECHARTABLE. This function expects one argument: the name of the character table remove.

    It’s an error to attempt to delete a character table that is currently in use or to attempt to delete a non-existing character table.

    Example:
        DELETECHARTABLE(mytable)

DELETECOUNTER
    DELETECOUNTER removes a definition of a counter that was defined by DEFINECOUNTER. This function expects one argument: the name of the counter to remove.

    If the counter does not exist, a warning is issued. It is not considered an error to try to delete a counter that has not been defined earlier.

    Example:
        DELETECOUNTER(mycounter)

DELETEMACRO
    DELETEMACRO removes a definition of a macro that was defined by DEFINEMACRO. This function takes one argument: the macro name to remove.

    There is no error condition (except for syntax errors): when no macro with a matching name was previously defined, no action is taken.

    For example, the safe way to define a macro is by first undefining it. This ensures that possible previous definitions are removed first:

    Example:
    DELETEMACRO(mymacro)

DELETENOUSERMACRO
    DELETENOUSERMACRO removes a `nousermacro’ definition. The function expects one argument: the name of the `nousermacro’ identifier to be removed from the nousermacro-set.

    There is no error condition (except for syntax errors): when the identifier wasn’t stored as a `nousermacro’ no action is taken.

    Example:
    DELETENOUSERMACRO(mymacro)

DELETESYMBOL
    DELETESYMBOL removes the definition of a symbol variable. It expects one parameter list, holding the name of the variable to deleted.

    This macro has no error condition (except for syntax errors): the symbol in question may be previously defined, but that is not necessary.

    Example:
        DELETESYMBOL(Options)

DUMMY
    This function is obsolete. It does nothing, and may be removed in future versions of Yodl.

ENDDEF
    ENDDEF is obsolete, and should be replaced by DECWSLEVEL. It may be removed in future versions of Yodl.

ERROR
    The ERROR function takes one argument: text to display to the standard error stream. The current input file and line number are also displayed. After displaying the text, the yodl program aborts with an exit status of 1.

    The text passed to the function is expanded first. See the example.

    The ERROR function is an example of a function that evaluates its parameter list itself.

    This command can be used, e.g., in a macro package when an incorrect macro is expanded. In my macro package (see chapter [MACROPACKAGE]) the ERROR function is used when the sectioning command chapter() is used in an article document (in the package, chapter’s are only available in books or reports).

    An analogous builtin function is WARNING, which also prints a message but does not exit (see section [WARNING]).

    Example: In the following call, COUNTERVALUE(NTRIES) is replaced by its actual value:
        ERROR(Stopping after COUNTERVALUE(NTRIES) attempts)

EVAL
    The EVAL function takes one argument: the text to be evaluated. This function allows you to perform an indirect evaluation of Yodl commands. Assume that there is a symbol varnam containing the name of a counter variable, then the following will display the value of the counter, incrementing it first:
        EVAL(NOTRANS(USECOUNTER)(SYMBOLVALUE(varnam)))

    The actions of the EVAL function can be described as follows:

o   First, the NOTRANS(USECOUNTER) is evaluated, producing USECOUNTER.

o   Next, the open parentheses is processed, producing the open parenthesis itself

o   Then, SYMBOLVALUE(varnam) is evaluated, producing the name of a counter, e.g. `counter’.

o   Eventually the closing parentheis is processed, producing the closing parenthesis itself.

o   All this results in the text
        USECOUNTER(counter)

o   This text is now presented to Yodl’s lexical scanner, resulting in incrementing the counter, and displaying its incremented value. It should be realized that macro arguments themselves are usually not evaluated. So, a construction like
        USECOUNTER(EVAL(SYMBOLVALUE(varnam)))

    will fail, since EVAL(SYMBOLVALUE(varnam)) is not a legal name for a counter: the EVAL() call is used here as an argument, which is not expanded. The distinction is subtle, and is caused by the fact that builtin functions receive unprocessed arguments, and may impose certain requirements on them (like USECOUNTER requiring the name of a counter).

    Summarizing: EVAL acts as follows:

o   Its argument is presented to Yodl’s lexical scanner

o   The output produced by the processing of the argument is then inserted into the input stream in lieu of the original EVAL call.

    Mosy built-in functions will not evaluate their arguments. In fact, only ERROR, EVAL, FPUTS, INTERNALINDEX, TYPEOUT, UPPERCASE and WARNING() will evaluate their arguments.

    Postponing evaluations allows you to write:
        DEFINESYMBOL(later)(SYMBOLVALUE(earlier))

    Eventually, and not when later is defined, a statement like
        SYMBOLVALUE(later)

    will produce the value of earlier at the moment SYMBOLVALUE(later) is processed. This is, in all its complex consequences, what would be expected in most cases. It allows us to write general macros producing output that is only evaluated when the text of symbols and values of arguments become eventually, rather than when the macro is defined, available.

    Decisions like these invariably result in questions like `what if I have to keep original values in some situation?’ In those situations EVAL() must be used. The following example shows the definition of three symbols: one receives an initial value, two will return one’s actual value when two’s value is displayed, three will, using EVAL(), store one’s initial value. The example also shows yet another way to suppress macro calls. It uses the macro nop() which is defined in the all standard conversion types.
        DEFINESYMBOL(one)(This is one, before)
        DEFINESYMBOL(two)(SYMBOLVALUE(one))
        EVAL(DEFINESYMBOL+nop()(three)(SYMBOLVALUE(one)))
        SETSYMBOL(one)(this is one, after)
        SYMBOLVALUE(two)
        SYMBOLVALUE(three)

FILENAME
    The function FILENAME() produces an absolute path to the currently processed Yodl file. This is not necessarily the canonical path name, as it may contain current- and parent-path directories.

FPUTS
    The function FPUTS expects two arguments: the first argment is information to be appended to a file, whose name is given as the second argument. The first argument is processed by Yodl before it is appended to the requested filename, so it may contain macro calls.

    For example, the following statement will append a countervalue to the mentioned file:
        FPUTS(There have been COUNTERVALUE(attempts) attempts)(/tmp/logfile)

    The second argument (name of the file) is not evaluated, but is used as received.

IFBUILTIN
    The IFBUILTIN function tests whether its first argument is the name of a builtin function. If so, the second parameter list is evaluated, else, the third parameter list is evaluated. All three parameter lists (the variable, the true-list and the false-list) must be present; though the true-list and/or the false-list may be empty parameter lists.

    Example:
        IFBUILTIN(IFBUILTIN)(\
            `BUILTIN’ is a builtin - function
        )(\
            `BUILTIN’ is NOT a builtin - function
        )

    Please note the preferred layout: The first argument immediately follows the function name, then the second argument (the true list) is indented, as is the false list. The layout closely follows the preferred layout of if-else statements of many programming languages.

IFCHARTABLE
    The IFCHARTABLE function tests whether its first argument is the name of a character table. The character table needs not be active. If the name is the name of a character table, the second parameter list is evaluated, else, the third parameter list is evaluated. All three parameter lists (the name, the true list and the false list) must be present; though the true list and/or the false list may be empty parameter lists.

    Example:
        IFCHARTABLE(standard)(\
            `standard’ is a character tablebuiltin - function
        )(\
            `standard’ is NOT a character tablebuiltin - function
        )

    Please note the preferred layout: The first argument immediately follows the function name, then the second argument (the true list) is indented, as is the false list. The layout closely follows the preferred layout of if-else statements of many programming languages.

IFDEF
    The IFDEF function tests for the definition status of the argument in its first parameter list. If it is a defined entity, the second parameter list is evaluated, else, the third parameter list is evaluated. All three parameter lists (the entity, the true list and the false list) must be present; though the true list and/or the false list may be empty parameter lists.

    The true list is evaluated if the first argument is the name of:

o   a built-in function, or

o   a character table, or

o   a counter, or

o   a no-user-macro symbol, or

o   a symbol, or

o   a user-defined macro, or Example:
        IFDEF(someName)(\
            `someName’ is a defined entity
        )(\
            `someName is not defined.
        )

    Please note the preferred layout: The first argument immediately follows the function name, then the second argument (the true list) is indented, as is the false list. The layout closely follows the preferred layout of if-else statements of many programming languages.

IFEMPTY
    IFEMPTY expects three arguments: a symbol, a true-list and a false-list. IFEMPTY evaluates to the true-list if the symbol is an empty string; otherwise, it evaluates to the false-list.

    The function does not further evaluate its argument. Its use is primarily to test whether a macro has received an argument or not. If the intent is to check whether a symbol’s value is empty or not, IFSTREQUAL [IFSTREQUAL] should be used, where the first argument is the name of a symbol, and the second argument is empty.

    Example:
        IFEMPTY(something)(\
            `something’ is empty...
        )(\
            `something’ is not an empty string
        )

    In the same way, IFEMPTY can be used to test whether an argument expands to a non-empty string. A more elaborate example follows below. Say you want to define a bookref macro to typeset information about an author, a book title and about the publisher. The publisher information may be absent, the macro then typesets unknown:
    \
        DEFINEMACRO(bookref)(3)(\
            Author(s):      ARG1
            Title:          ARG2
            Published by:   \
            IFEMPTY(ARG3)
            (\
                Unknown\
            )(\
                ARG3\
            )
        )

    Using the macro, as in:
    \
        bookref(Helmut Leonhardt)
               (Histologie, Zytologie und Microanatomie des Menschen)
               ()

    would now result in the text Unknown behind the Published by: line.

    Please note the preferred layout: The first argument immediately follows the function name, then the second argument (the true list) is indented, as is the false list. The layout closely follows the preferred layout of if-else statements of many programming languages.

IFEQUAL
    IFEQUAL expects four argument lists. It tests whether its first argument is equal to its second argument. If so, the third parameter list is evaluated, else, the fourth parameter list is evaluated. All four argument lists must be present, though all can be empty lists.

    The first two arguments of IFEQUAL should be integral numerical arguments. In order to determine whether the first two arguments are equal, their values are determined:

o   If the argument starts with an integral numerical value, that value is the value of the argument.

o   If the argument is the name of a counter, the counter’s value is the value of the argument

o   If the values of the first two arguments van be determined accordingly, their equality will determine whether the true list (when the values are equal) or the false list (when the values are unequal) will be evaluated.

o   Otherwise, IFEQUAL will evaluate the false list.

    Example:
        IFEQUAL(0)()(\
            0 and an empty string are equal
        )(\
            0 and an empty string are not equal
        )

    Please note the preferred layout: The first argument immediately follows the function name, then the second argument (the true list) is indented, as is the false list. The layout closely follows the preferred layout of if-else statements of many programming languages.

IFGREATER
    IFGREATER expects four argument lists. It tests whether its first argument is greater to its second argument. If so, the third parameter list is evaluated, else, the fourth parameter list is evaluated. All four argument lists must be present, though all can be empty lists.

    The first two arguments of IFGREATER should be integral numerical arguments. In order to determine whether the first two arguments are equal, their values are determined:

o   If the argument starts with an integral numerical value, that value is the value of the argument.

o   If the argument is the name of a counter, the counter’s value is the value of the argument

o   If the values of the first two arguments van be determined accordingly, their order relation will determine whether the true list (when the first value is greater than the second value) or the false list (when the first value is smaller or equal than the second value) will be evaluated.

o   Otherwise, IFGREATER will evaluate the false list.

    Example:
        IFGREATER(counter)(5)(\
            counter exceeds the value 5
        )(\
            counter does not exceeds the value 5, or counter is no Yodl-counter.
        )

    Please note the preferred layout: The first argument immediately follows the function name, then the second argument (the true list) is indented, as is the false list. The layout closely follows the preferred layout of if-else statements of many programming languages.

IFMACRO
    The IFMACRO function tests whether its first argument is the name of a macro. If the name is the name of a macro, the second parameter list is evaluated, else, the third parameter list is evaluated. All three parameter lists (the name, the true list and the false list) must be present; though the true list and/or the false list may be empty parameter lists.

    Example:
        IFMACRO(nested)(\
            `nested’ is the name of a macro
        )(\
            There is no macro named `nested’
        )

    Please note the preferred layout: The first argument immediately follows the function name, then the second argument (the true list) is indented, as is the false list. The layout closely follows the preferred layout of if-else statements of many programming languages.

IFSMALLER
    IFSMALLER expects four argument lists. It tests whether its first argument is smaller to its second argument. If so, the third parameter list is evaluated, else, the fourth parameter list is evaluated. All four argument lists must be present, though all can be empty lists.

    The first two arguments of IFSMALLER should be integral numerical arguments. In order to determine whether the first two arguments are equal, their values are determined:

o   If the argument starts with an integral numerical value, that value is the value of the argument.

o   If the argument is the name of a counter, the counter’s value is the value of the argument

o   If the values of the first two arguments van be determined accordingly, their order relation will determine whether the true list (when the first value is smaller than the second value) or the false list (when the first value is greater than or equal to the second value) will be evaluated.

o   Otherwise, IFSMALLER will evaluate the false list.

    Example:
        IFSMALLER(counter)(5)(\
            counter is smaller than the value 5, or counter is no Yodl-counter
        )(\
            counter exceeds the value 5
        )

    Please note the preferred layout: The first argument immediately follows the function name, then the second argument (the true list) is indented, as is the false list. The layout closely follows the preferred layout of if-else statements of many programming languages.

IFSTREQUAL
    IFSTREQUAL tests for the equality of two strings. It expects four arguments: two strings to match, a true list and a false list. The true list is only evaluated when the contents of the two string arguments exactly match.

    The first two arguments of IFSTREQUAL are partially evaluated:

o   If the argument is the name of a symbol, the symbol’s value is the value of the argument

o   Otherwise, the argument itself is used.

    In the degenerate case where the string to be compared is actually the name of a SYMBOL, use a temporary SYMBOL variable containing the name of that symbol, and compare it to whatever you want to compare it with. Alternatively, write a blank space behind the arguments, since the arguments are then interpreted `as is’. In practice, the need for these constructions seem to arise seldomly, however.

    Example:
        IFSTREQUAL(MYSYMBOL)(Hello world)(
            The symbol `MYSYMBOL’ holds the value `Hello world’
        )(
            The symbol `MYSYMBOL’ doesn’t hold the value `Hello world’
        )

IFSTRSUB
    IFSTRSUB tests whether a string is a sub-string of another string. It acts similar to IFSTREQUAL, but it tests whether the second string is part of the first one.

    The first two arguments of IFSTREQULA are partially evaluated:

o   If the argument is the name of a symbol, the symbol’s value is the value of the argument

o   Otherwise, the argument itself is used.

    In the degenerate case where the string to be compared is actually the name of a SYMBOL, use a temporary SYMBOL variable containing the name of that symbol, and compare it to whatever you want to compare it with. Alternatively, write a blank space behind the arguments, since the arguments are then interpreted `as is’. In practice, the need for these constructions seem to arise seldomly, however.

    Example:
            IFSTRSUB(haystack)(needle)(
                `needle’ was found in `haystack’
            )(
                `needle’ was not found in `haystack’
            )

    Note that both `haystack’ and `needle’ may be the names of symbols. If they are, their contents are is compared, rather than the literal names `haystack’ and `needle’

IFSYMBOL
    The IFSYMBOL function tests whether its first argument is the name of a symbol. If it is the name of a symbol, the second parameter list is evaluated, else, the third parameter list is evaluated. All three parameter lists (the name, the true list and the false list) must be present; though the true list and/or the false list may be empty parameter lists.

    Example:
        IFSYMBOL(nested)(\
            `nested’ is the name of a symbol
        )(\
            There is no symbol named `nested’
        )

    Please note the preferred layout: The first argument immediately follows the function name, then the second argument (the true list) is indented, as is the false list. The layout closely follows the preferred layout of if-else statements of many programming languages.

IFZERO
    IFZERO expects three parameter lists. The first argument defines whether the whole function expands to the true list or to the false list.

    The first argument of IFZERO should be an integral numerical value. Its value is determined as follows:

o   If the argument starts with an integral numerical value, that value is the value of the argument.

o   If the argument is the name of a counter, the counter’s value is the value of the argument

o   Otherwise, IFZERO will evaluate the false list.

    Note that, starting with Yodl version 2.00 the first argument is not evaluated any further. So, COUNTERVALUE(somecounter) will always be evaluated as 0. If the value of a counter is required, simply provide its name as the first argument of the IFZERO function.

    Example:
        DEFINEMACRO(environment)(2)(\
            IFZERO(ARG2)(\
                NOEXPAND(\end{ARG1})\
            )(\
                NOEXPAND(\begin{ARG1})\
            )\
        )

    Such a macro may be used as follows:
        environment(center)(1)
            Now comes centered text.
        environment(center)(0)

    which would of course lead to \begin and \end{center}. The numeric second argument is used here as a on/off switch.

INCLUDEFILE
    INCLUDEFILE takes one argument, a filename. The file is processed by Yodl. If a file should be inserted without processing the builtin function NOEXPANDINCLUDE [NOEXPANDINCLUDE] or NOEXPANDPATHINCLUDE [NOEXPANDPATHINCLUDE] should be used.

    The yodl program supplies, when necessary, an extension to the filename. The supplied extension is .yo, unless defined otherwise during the compilation of the program.

    Furthermore, Yodl tries to locate the file in the Yodl’s include path (which may be set using the --include option). The actual value of the include path is shown in the usage information, displayed when Yodl is started without arguments.

    NOTE: Starting with Yodl version 3.00.0 Yodl’s default file inclusion behavior has changed. The current working directory no longer remains fixed at the directory in which Yodl is called, but is volatile, changing to the directory in which a yodl-file is located. This has the advantage that Yodl’s file inclusion behavior now matches the way C’s #include directive operates; it has the disadvantage that it may break some current documents. Conversion, however is simple and can be avoided altogether if Yodl’s -L (--legacy-include) option is used.

    Example:
        INCLUDEFILE(latex)

    will try to include the file latex or latex.yo from the current include parth. When the file is not found, Yodl aborts.

INCLUDELIT, INCLUDELITERAL
    INCLUDELIT and INCLUDELITERAL are obsolete. NOEXPANDINCLUDE [NOEXPANDINCLUDE] or NOEXPANDPATHINCLUDE [NOEXPANDPATHINCLUDE] should be used instead.

INCWSLEVEL
    INCWSLEVEL requires one (empty) parameter list. It increases the current white-space level. The white-space level typically is used in files that only define Yodl macros. When no output should be generated while processing these files, the white-space level can be used to check for this. If the white-space level exceeds zero, a warning will be generated if the file produces non-whitespace output. The builtin function DECWSLEVEL is used to reduce the whitespace level following a previous call of INCWSLEVEL.

    Once the white space level exceeds zero, no output will be generated. White space, therefore will effectively be ignored. The white space level cannot be reduced to negative values. A warning is issued if that would have happened if it were allowed.

    Example:
        INCWSLEVEL()
        DEFINESYMBOL(....)
        DEFINEMACRO(...)(...)(...)
        DECWSLEVEL()

    Without the INCWSLEVEL and DECWSLEVEL, calls, the above definition would generate four empty lines to the output stream.

    The INCWSLEVEL and DECWSLEVEL calls may be nested. The best approach is to put an INCWSLEVEL at the first line of a macro-defining Yodl-file, and a matching DECWSLEVEL call at the very last line.

INTERNALINDEX
    INTERNALINDEX expects one argument list. The argument list is evaluated and written to the index file.

    The index file is defined since Yodl version 2.00, and contains the fixup information which was previously written to Yodl’s output as the .YODLTAGSTART. ... .YODLTAGEND. sequence.

    The index file allows for greated processing speed, at the expense of an additional file. The associated yodlpost postprocessing program will read and process the index file, and will fixup the corresponding yodl-output accordingly.

    The index file is not created when output is written to the standard output name, since Yodl is unable to request the system for the current file offset.

    The entries of the index file always fit on one line. INTERNALINDEX will alter newline characters in its argument into single blank spaces. Each line starts with the current offset of Yodl’s output file, thus indicating the exact location where a fixup is requested. An example of a produced fixup line could be
        3004 ref MACROPACKAGE

    indicating that at offset 3004 in the produced output file a reference to the label MACROPACKAGE is requested. Assuming a html conversion, The postprocessor will thereupon write something like
        <a href="outfile04.html#MACROPACKAGE">4.3.2.</a>

    into the actual output file while processing Yodl’s output up to offset location 3004.

    Consequently, producing Yodl-output normally consists of two steps:

o   First, Yodl itself is started, producing, e.g., out.idx (the index file) and out.yodl (Yodl’s raw output).

o   Then, Yodl’s post-processor processes out.idx and out.yodl, producing one or more final output files, in which the elements of the index file have been properly handled. This may result in multiple output file, like report.html, report01.html, report02.html etc.

NEWCOUNTER
    NEWCOUNTER is obsolete. DEFINECOUNTER [DEFINECOUNTER] should be used instead.

NOEXPAND
    NOEXPAND is used to send text to the final output file without being expanded by Yodl (the other methods are the CHAR macro, see section [CHAR], and the NOTRANS macro, see section [NOTRANS]). NOEXPAND takes one parameter list, the text in question. Whatever occurs in the argument is not subject to parsing or expansion by Yodl, but is simply copied to the output file (except for CHAR functions in the argument, which are expanded. If CHAR-expansion is not required either NOTRANS [NOTRANS] can be used).

    Furthermore, the contents of the parameter list are also subject to character table translations, using the currently active table. This should come as no surprise. Ignoring character tables would make both the processing of CHAR calls and the NOTRANS function superfluous.

    So, the following situations are recognized:
     | support chartables
     | and CHAR
    Macro expansion | yes | no
    Yes | (standard) | Push chartable
     |  | (standard)
     |  | Pop chartable
    No | NOEXPAND | NOTRANS
    E.g., let’s assume that you need to write in your document the following text:
        INCLUDEFILE(something or the other)
        IFDEF(onething)(
            ...
        )(
            ....
        )
        NOEXPAND(whatever)

    The way to accomplish this is by prefixing the text by NOEXPAND followed by an open parenthesis, and by postfixing it by a closing parenthesis. Otherwise, the text would be expanded by Yodl while processing it (and would lead to syntax errors, since the text isn’t correct in the sence of the Yodl language).

    For this function, keep the following caveats in mind:

o   There is only one thing that a NOEXPAND cannot protect from expansion: an ARGx in a macro definition. The argument specifier is always processed. E.g., after
        DEFINEMACRO(thatsit)(1)(
            That is --> NOEXPAND(ARG1) <-- it!
        )
        thatsit(after all)

    the ARG1 inside the NOEXPAND statement is replaced with after all.

o   The NOEXPAND function must, as all functions, be followed by a parameter list. The parentheses of the list must therefore be `balanced’. For unbalanced lists, use CHAR(40) to set an open parenthesis, or CHAR(41) to typeset a closing parenthesis.

NOEXPANDINCLUDE
    NOEXPANDINCLUDE takes one argument, a filename. The file is included.

    The filename is uses as specified. The include path is not used when locating this file.

    NOTE: Starting with Yodl version 3.00.0 Yodl’s default file inclusion behavior has changed. The current working directory no longer remains fixed at the directory in which Yodl is called, but is volatile, changing to the directory in which a yodl-file is located. This has the advantage that Yodl’s file inclusion behavior now matches the way C’s #include directive operates; it has the disadvantage that it may break some current documents. Conversion, however is simple and can be avoided altogether if Yodl’s -L (--legacy-include) option is used.

    The argument to NOEXPANDINCLUDE is partially evaluated:

o   If the argument is the name of a symbol, the symbol’s value is the value of the argument

o   Otherwise, the argument itself is used. The thus obtained file name is not further evaluated: in particular, it will not be subject to character translations.

    The contents of the file are included literally, not subject to macro expansion. Character translations are performed, though. If character translations are not appropriate, PUSHCHARTABLE can be used to suppress character table translations temporarily.

    The purpose of NOEXPANDINCLUDE is to include source code literally in the document, as in:
        NOEXPANDINCLUDE(literal.c)

    The function NOEXPANDPATHINCLUDE can be used to insert a file which is located in one of the directories specified in Yodl’s include path.

NOEXPANDPATHINCLUDE
    NOEXPANDPATHINCLUDE takes one argument, a filename. The file is included. The file is searched for in the directories specified in Yodl’s includepath.

    NOTE: Starting with Yodl version 3.00.0 Yodl’s default file inclusion behavior has changed. The current working directory no longer remains fixed at the directory in which Yodl is called, but is volatile, changing to the directory in which a yodl-file is located. This has the advantage that Yodl’s file inclusion behavior now matches the way C’s #include directive operates; it has the disadvantage that it may break some current documents. Conversion, however is simple and can be avoided altogether if Yodl’s -L (--legacy-include) option is used.

    The argument to NOEXPANDPATHINCLUDE is partially evaluated:

o   If the argument is the name of a symbol, the symbol’s value is the value of the argument

o   Otherwise, the argument itself is used. The thus obtained file name is not further evaluated: in particular, it will not be subject to character translations.

    Like the NOEXPANDINCLUDE function, the contents of the file are included literally, not subject to macro expansion. Character translations are performed, though. If character translations are not appropriate, PUSHCHARTABLE [PUSHCHARTABLE] can be used to suppress character table translations temporarily.

    The purpose of NOEXPANDPATHINCLUDE is to include source code as defined in a macro package literally into the document, as in:
        NOEXPANDPATHINCLUDE(rug-menubegin.xml)

NOTRANS
    NOTRANS copies its one argument literally to the output file, without expanding macros in it and without translating the characters with the current translation table. The NOTRANS function is typically used to send commands for the output format to the output file.

    For example, consider the following code fragment:
        COMMENT(--- Define character translations for \, { and } in LaTeX. ---)
        DEFINECHARTABLE(standard)(
            ’\\’    =    "$\\backslash$"
            ’{’     =    "\\verb+{+"
            ’}’     =    "\\verb+}+"
        )

        COMMENT(--- Activate the translation table. ---)
        USECHARTABLE(standard)

        COMMENT(--- Now two tests: ---)

        NOEXPAND(\input{epsf.tex})
        NOTRANS(\input{epsf.tex})

    NOEXPAND will send
        $\backslash$input\verb+{+epsf.tex\verb+}+

    since the characters in its argument are translated with the standard translation table. In contrast, NOTRANS will send \input{epsf.tex}.

    The parameter list of NOTRANS must be balanced with respect to its parentheses. When using an unbalanced set of parentheses, use CHAR(40) to send a literal (, or CHAR(41) to send a ).

    The NOEXPAND description summarizes all combinations of character translations and/or macro expansion, and how they are handled and realized by Yodl.

NOUSERMACRO
    NOUSERMACRO controls yodl’s warnings in the following way: When Yodl is started with the -w flag on the command line, then warnings are generated when Yodl encounters a possible macro name, followed by a parameter list, without finding a macro by that name. Yodl then prints something like cannot expand possible user macro.

    Examples of such sequences are, The necessary file(s) are in /usr/local/lib/yodl, or see the manual page for sed(1). The candidate macros are file and sed; these names could just as well be `valid’ user macros followed by their parameter list.

    When a corresponding NOUSERMACRO statement appears before yodl encounters the candidate macros, no warning is generated. A fragment might therefore be:
        NOUSERMACRO(file sed)
        The necessary file(s) are in ...
        See the manual page for sed(1).

    The NOUSERMACRO accepts one or more names in its argument, separated by white space, commas, colons, or semi-colons.

OUTBASE
    OUTBASE inserts the current basename of the output file into the output file. The basename is the name of the file of which the directory components and extension were stripped.

    If the output file is the standard output file, - is inserted.

OUTDIR
    OUTDIR inserts the current path name of the output file into the output file. The path name is a, not necessarily absolute, designator of the directory in which the output file is located. If the output file is indicated as, e.g., -o out, then OUTDIR simply inserts a dot.

    If the output file is the standard output file, a dot is inserted too.

OUTFILENAME
    OUTFILENAME inserts the current filename of the output file into the output file. The filename is the name of the file of which the directory components were stripped.

    If the output file is the standard output file, - is inserted.

PARAGRAPH
    PARAGRAPH isn’t really a builtin function, but as it is handled especially by Yodl, it is described here nonetheless. Starting with Yodl 2.00 PARAGRAPH operates as follows:

    If the macro is not defined, new paragraphs, defined as series of consecutive empty lines written to the output stream, are not handled different from any other series of characters sent to the output stream. I.e., they are inserted into that stream.

    However, if the macro has been defined, Yodl will call it whenever a new paragraph (defined as a series of at least two blank lines) was recognized.

    The empty lines that were actually recognized may be obtained inside the PARAGRAPH macro from the XXparagraph symbol, if this symbol has been be defined by that time. If defined, it will contain the white space that caused Yodl to call the PARAGRAPH macro.

    Note that, in order to inspect XXparagraph it must have been defined first. Yodl itself will not define this symbol itself.

    The PARAGRAPH macro should be defined as a macro not expecting arguments. The macro is thus given a chance to process the paragraph in a way that’s fitting for the particular conversion type. If the PARAGRAPH macro produces series of empty lines itself, then those empty lines will not cause Yodl to activate PARAGRAPH. So, Yodl itself will not recursively call PARAGRAPH, although the macro could call itself recursively. Of course, such recursive activcation of PARAGRAPH is then the sole responsibility of the macro’s author, and not Yodl’s.

    Some document languages do not need paragraph starts; e.g., LaTeX handles its own paragraphs. Other document languages do need it: typically, PARAGRAPH is then defined in a macro file to trigger some special action. E.g., a HTML converter might define a paragraph as:
        DEFINEMACRO(PARAGRAPH)(0)(
            XXnl()
            NOTRANS(<p>)
        )

    A sytem like xml has more strict requirements. Paragraphs here must be opened and closed using pairs of <p> and </p> tags. In those cases an auxiliary counter can be used to indicate whether there is an open paragraph or not. The PARAGRAPH macro could check for this as follows, assuming the availability of a counter XXp:
        DEFINEMACRO(PARAGRAPH)(0)(
            XXnl()
            IFZERO(XXp)(
            )(
                NOTRANS(</p>)
            )
            NOTRANS(<p>)
            SETCOUNTER(XXp)(1)
        )

    Note that the above fragment exemplifies an approach, not necessarily the implementation of the PARAGRAPH macro for an xml-convertor.

PIPETHROUGH
    The builtin function PIPETHROUGH is, besides SYSTEM, the second function with which a Yodl document can affect its environment. Therefore, the danger of `live data’ exists which is also described in the section about SYSTEM (see section [SYSTEM]). Nevertheless, PIPETHROUGH can be very useful. It is intended to use external programs to accomplish special features. The idea is that an external command is started, to which a block of text from within a Yodl document is `piped’. The output of that child program is piped back into the Yodl document; hence, a block of text is `piped through’ an external program. Whatever is received again in the Yodl run, is further processed.

    The PIPETHROUGH function takes two arguments:

o   the command to run, and

o   the text to send to that command.

    Functionally, the occurrence of the PIPETHROUGH function and of its two arguments is replaced by whatever the child program produces on its standard output.

    An example might be the inclusion of the current date, as in:

    The current date is:
    PIPETHROUGH(date)()

    In this example the command is date and the text to send to that program is empty.

    The main purpose of this function is to provide a way by which external programs can be used to create, e.g., tables or figures for a given output format. Further releases of Yodl may contain such dedicated programs for the output formats.

POPCHARTABLE
    Character tables which are pushed onto the table stack using PUSHCHARTABLE() are restored (popped) using POPCHARTABLE(). For a description of this mechanism please refer to section [PUSHINGTABLES].

POPCOUNTER
    POPCOUNTER is used to remove the topmost counter from the counter stack. The values of counters may be pushed on a stack using PUSHCOUNTER [PUSHCOUNTER]. To remove the topmost element of a counter’s stack POPCOUNTER is available. POPCOUNTER expects one argument: the name of the counter to pop. The previously pushed value then becomes the new value of the counter. A counter’s value may be popped after defining it, whereafter the stack will be empty, but the counter will still be defined. In that case, using the counter’s value is considered an error.

    Examples:
        DEFINECOUNTER(YEAR)(1950)
        POPCOUNTER(YEAR)
        COMMENT(YEAR now has an undefined value)

    See also section [COUNTERS].

POPMACRO
    POPMACRO is used to remove the actual macro definition, restoring a previously pushed definition. The values of macros may be pushed on a stack using PUSHMACRO. To remove the topmost element of a macro’s stack POPMACRO is available. POPMACRO expects one argument: the name of the macro to pop. The previously pushed value then becomes the new value of the macro.

    A macro’s value may be popped after defining it, whereafter the stack will be empty, but the macro will still be defined. In that case, using the macro is considered an error.

    Example:
        DEFINEMACRO(Hello)(1)(Hello, ARG1, this is a macro definition)
        Hello(Karel)
        PUSHMACRO(Hello)(1)(Hello, ARG1, this is the new definition)
        Hello(Karel)
        POPMACRO(Hello)
        Hello(Karel)
        COMMENT(The third activation of Hello() produces the same output
                as the first activation)

POPSYMBOL
    POPSYMBOL is used to remove the topmost symbol from the symbol stack. The values of symbols may be pushed on a stack using PUSHSYMBOL [PUSHSYMBOL]. To remove the topmost element of a symbol’s stack POPSYMBOL is available.

    POPSYMBOL expects one argument: the name of the symbol to pop. The previously pushed value then becomes the new value of the symbol. A symbol’s value may be popped after defining it, whereafter the stack will be empty, but the symbol will still be defined. In that case, using the symbol’s value is considered an error.

    Example:
        DEFINESYMBOL(YEAR)(This happened in 1950)
        POPSYMBOL(YEAR)
        COMMENT(YEAR now has an undefined value)

POPWSLEVEL
    POPWSLEVEL is used to remove the topmost wslevel from the wslevel stack. The values of wslevels may be pushed on a stack using PUSHWSLEVEL [PUSHWSLEVEL]. See also section DECWSLEVEL [DECWSLEVEL]

    To remove the topmost element of a wslevel’s stack POPWSLEVEL is available. POPWSLEVEL expects one argument: the name of the wslevel to pop. The previously pushed value then becomes the new value of the wslevel. A wslevel’s value may be popped after defining it, whereafter the stack will be empty, but the wslevel will still be defined. In that case, using the wslevel’s value is considered an error.

    Example:
        COMMENT(Assume WS level is zero)

        PUSHWSLEVEL(1)
        COMMENT(WS level now equals 1)
        POPWSLEVEL()
        COMMENT(WS level now equals 0 again)

PUSHCHARTABLE
    Once a character table has been defined, it can be pushed onto a stack using PUSHCHARTABLE. The pushed chartable may be popped later. PUSHCHARTABLE is described in more detail in section [PUSHINGTABLES].

PUSHCOUNTER
    PUSHCOUNTER is used to start another lifetime for a counter, pushing its current value on a stack. A stack is available for each individual counter.

    PUSHCOUNTER expects two arguments: the name of the counter to push and its new value after pushing. When the second argument is an empty parameter list, the new value will be zero. The new value may be specified as a numerical value, or as the name of an existing counter. Specify the name of the counter twice to merely push its value, without modifying its current value.

    Examples:
        DEFINECOUNTER(YEAR)(1950)
        PUSHCOUNTER(YEAR)(1962)
        COMMENT(YEAR now has the value 1962, and a pushed value of 1950)

    See also section [COUNTERS].

PUSHMACRO
    PUSHMACRO is used to start another lifetime for a macro, pushing its current definition on a stack. A stack is available for each individual macro.

    PUSHMACRO expects three arguments: the name of the macro to push, the number of its arguments after pushing (which may be different from the number of arguments interpreted by the pushed macro) and its new definition.

    So, PUSHMACRO is used exactly like DEFINEMACRO, but will redefine a current macro (or define a new macro if no macro was defined by the name specified as its first argument.

    Example:
        DEFINEMACRO(Hello)(1)(Hello, ARG1, this is a macro definition)
        Hello(Karel)
        PUSHMACRO(Hello)(1)(Hello, ARG1, this is the new definition)
        Hello(Karel)
        POPMACRO(Hello)
        Hello(Karel)
        COMMENT(The third activation of Hello() produces the same output
                as the first activation)

PUSHSYMBOL
    PUSHSYMBOL is used to start another lifetime for a symbol, pushing its current value on a stack. A stack is available for each individual symbol.

    PUSHSYMBOL expects two arguments: the name of the symbol to push and its new value after pushing. When the second argument is an empty parameter list, the new value will be zero. The new value may be specified as a numerical value, or as the name of an existing symbol. Specify the name of the symbol twice to merely push its value, without modifying its current value.

    Examples:
        DEFINESYMBOL(YEAR)(This happened in 1950)
        PUSHSYMBOL(YEAR)(This happended in 1962)
        COMMENT(YEAR now has the value `This happended in 1962’ and a
                pushed value of `This happened in 1950’)

PUSHWSLEVEL
    PUSHWSLEVEL is used to start another lifetime of the white-space level pushing the level’s current value on a stack. See also section INCWSLEVEL [INCWSLEVEL]

    PUSHWSLEVEL expects one argument, the new value of the white-space level. This value may be specified as a numerical value or as the name of a counter. The argument may be empty, in which the new value will be zero.

    Example:
        COMMENT(Assume WS level is zero)

        PUSHWSLEVEL(1)
        COMMENT(WS level now equals 1)
        POPWSLEVEL()
        COMMENT(WS level now equals 0 again)

RENAMEMACRO
    RENAMEMACRO takes two arguments: the name of a built-in macro (such as INCLUDEFILE) and its new name.

    E.g., after
        RENAMEMACRO(INCLUDEFILE)(include)

    a file must be included by include(file). INCLUDEFILE can no longer be used for this: following the RENAMEMACRO action, the old name can no longer be used; it becomes an undefined symbol.

    If you want to make an alias for a built-in command, do it with DEFINEMACRO. E.g., after:
        DEFINEMACRO(include)(1)(INCLUDEFILE(ARG1))

    both INCLUDEFILE and include can be used to include a file.

SETCOUNTER
    SETCOUNTER expects two parameter lists: the name of a counter, and a numeric value or the name of another counter.

    The corresponding counter (which must be previously created with NEWCOUNTER) is set to, respectively, the numeric value or the value of the other counter.

    See also section [COUNTERS].

SETSYMBOL
    SETSYMBOL expects two parameter lists: the name of a symbol, and the text to assign to the named symbol.

STARTDEF
    STARTDEF is obsolete. Instead, INCWSLEVEL [INCWSLEVEL] should be used.

SUBST
    SUBST is a general-purpose substitution mechanism for strings in the input. SUBST takes two arguments: a search string and a substitution string. E.g., after
        SUBST(VERSION)(1.00)

    YODL will transorm all occurrences of VERSION in its input into 1.00.

    SUBST is also useful in situations where multi-character sequences should be converted to accent characters. E.g., a LaTeX converter might define:
        SUBST(’e)(NOTRANS(\’{e}))

    Each ’e in the input will then be converted to e.

    SUBST may be useed in combination with the command line flag -P, as in a invocation
        yodl2html -P’SUBST(VERSION)(1.00)’ myfile.yo

    Another useful substitution might be:
        SUBST(_OP_)(CHAR(40))
        SUBST(_CP_)(CHAR(41))

    which defines an opening parenthesis (_OP_) and a closing parenthesis (_CP_) as mapped to the CHAR function. The strings _OP_ and _CP_ might then be used to produce unbalanced parameter lists.

    Note that:

o   The first argument of the SUBST command, the search string, is taken literally. Yodl does not expand it; the string must be literally matched in the input.

o   The second argument, the replacement, is further processed by Yodl. Protect this text by NOTRANS or NOEXPAND where appropriate.

    Substitutions occur extremely early while YODL processes its input files. In order to processs its input files, YODL takes the following basic steps:

1.  It requests input from its lexical scanner (so-called tokens)

2.  Its parser processes the tokens produced by the lexical scanner

3.  Its parser may send text to an output `object’, which will eventually appear in the output file generated by YODL. YODL will perform all macro substitutions in step 2, and all character table conversions in step 3. However, the lexical scanner has access to the SUBST definitions: as soon as its lexical analyzer detects a series of characters matching the defining sequence of a SUBST definition, it will replace that defining sequence by its definition. That definition is then again read by the lexical scanner. Of course, this definition may, in turn, contain defining sequences of other SUBST definitions: these will then be replaced by their definitions as well. This implies:

o   Circular definitions may cause the lexical scanner to get stuck in a replacement loop. It is the responsibility of the author defining SUBST definitions to make sure that this doesn’t happen.

o   Neither the parser, nor the output object ever sees the SUBST defining character sequences: they will only see their definitions.

SYMBOLVALUE
    SYMBOLVALUE expands to the value of a symbol. Its single parameter list must contain the name of a symbol. The symbol must have been created earlier using the builtin DEFINESYMBOL.
    Example:
        The symbol has value SYMBOLVALUE(MYSYMBOL).

SYSTEM
    SYSTEM takes one argument: a command to execute. The command is run via the standard C function system. The presence of this function in the Yodl language introduces the danger of live data. Imagine someone sending you a document containing
        SYSTEM(rm *)

    To avoid such malevolent side effects, YODL has a flag -l to define the `live data policy’. By default, -l0 is implied which suppresses the SYSTEM function and the related PIPETHROUGH function. See also section [USING].

    Despite the potential danger, SYSTEM can be useful in many ways. E.g., you might want to log when someone processes your document, as in:
        SYSTEM(echo Document processed! | mail myself@my.host)

    Note that SYSTEM merely performs an system-related task. It’s a process that is separated from the YODL process itself. One of the consequences of this is that any output generated by SYSTEM will not normally appear into YODL’s output file. If the output of a subprocess should be inserted into YODL’s output file, either use PIPETHROUGH [PIPETHROUGH], or insert a temporary file as shown in the following example:
        SYSTEM(date > datefile)
        The current date is:
        INCLUDEFILE(datefile)
        SYSTEM(rm datefile)

TYPEOUT
    TYPEOUT requires one parameter list. The text of the list is sent to the standard error stream, followed by a newline. This feature can be handy to show, e.g., messages such as version numbers in macro package files.

    Example: The following macro includes a file and writes to the screen that this file is currently processed.
        DEFINEMACRO(includefile)(1)(
            TYPEOUT(About to process document: ARG1)
            INCLUDEFILE(ARG1)
        )

UNDEFINEMACRO
    UNDEFINEMACRO is deprecated. Use DELETEMACRO [DELETEMACRO] instead.

UPPERCASE
    UPPERCASE converts a string or a part of it to upper case. It has two arguments:

o   The string to convert;

o   A length, indicating how many characters (starting from the beginning of the string) should be converted. The length indicator can be smaller than one or larger than the length of the string; in that case, the whole string is convertered.

    Example:
        UPPERCASE(hello world)(1)
        UPPERCASE(hello world)(5)
        UPPERCASE(hello world)(0)

    This code sample expands to:
        Hello world
        HELLO world
        HELLO WORLD

USECHARTABLE
    USECHARTABLE takes one parameter list: the name of a translation table to activate. The table must previously have been defined using DEFINECHARTABLE. See section [CHARTABLES] for a description of character translation tables.

    Alternatively, the name may be empty in which case the default character mapping is restored.

USECOUNTER
    USECOUNTER is a combination of ADDTOCOUNTER and COUNTERVALUE. It expects one parameter list: the name of an defined counter (see DEFINECOUNTER [DEFINECOUNTER]).

    The counter is first incremented by 1. Then the function expands to the counter’s value.

    See also section [COUNTERS].

VERBOSITY
    VERBOSITY expects two arguments, and may be used to change the verbosity level inside YODL files. The function may be used profitably for debugging purposes, to debug the expansion of a macro or the processing of a YODL input file.

    The first argument indicates the procesing mode of the second argument, and it may be:

o   Empty, in which case the message-level is set to the value specified in the second argument;

o   +, in which case the value specified in the second argument augments the current message level;

o   -, in which case the value specified in the second argument augments is removed from the current message level

    The second argument specifies one or more, separated by blanks, message level names or it may be set to a hexadecimal value (starting with 0x), using hexadecimal values to represent message levels. Also, NONE may be used, to specify no message level, or ALL can be used to specify all message levels.

    The following message levels are defined:

o   ALERT (0x40). When an alert-error occurs, Yodl terminates. Here Yodl requests something of the system (like a get_cwd()), but the system fails.

o   CRITICAL (0x20). When a critical error occurs, Yodl terminates. The message itself can be suppressed, but exiting can’t. A critical condition is, e.g., the omission of an open parenthesis at a location where a parameter list should appear, or a non-existing file in an INCLUDEFILE specification (as this file should be parsed). A non-existing file with a NOEXPANDINCLUDE specification is a plain (non-critical) error.

o   DEBUG (0x01). Probably too much info, like getting information about each character that was read by Yodl.

o   ERROR (0x10). An error (like doubly defined symbols). Error messages will not stop the parsing of the input (up to a maximum number of errors), but no output is generated.

o   INFO (0x02). Not as detailed as `debug’, but still very much info, like information about media switches.

o   NOTICE (0x04). Information about, e.g., calls to the builtin function calls.

o   WARNING (0x08). Something you should know about, but probably not affecting Yodl’s proper functioning

    There also exists a level EMERG (0x80) which cannot be suppressed.

    The value 0x00 represents NONE, the value 0xff represents ALL.

    When specifying multiple message levels using the hexadecimal form, their hexadecimal values should be binary-or-ed: adding them is ok, as long as you don’t specify ALL:
        VERBOSITY()(0x06)
        COMMENT(this specifies `INFO’ and `NOTICE’)

    When specifying message levels by their names, the names may be truncated at a unique point. However, the message level names are interpreted case sensitively, so INF for INFO is recognized as such, but info for INFO isn’t. The following examples all specify verbosity levels INFO and NOTICE:
        VERBOSITY()(I N)
        VERBOSITY()(N I)
        VERBOSITY()(NOT IN)
        VERBOSITY()(INFO NOTICE)

WARNING
    WARNING takes one argument: text to display as a warning. The yodl program makes sure that before showing the text, the current file and line number are printed. Other than this, WARNING works just as TYPEOUT (see section [TYPEOUT]).

    Note that an analogous function ERROR exists, which prints a message and then terminates the program (see section [ERROR]).

WRITEOUT
    WRITEOUT is deprecated, use FPUTS [FPUTS] instead.

FILES
The files in /usr/local/share/yodl-3.00.0 define the converter’s macro packages. The scripts yodl2tex, yodl2html, yodl2man etc. perform the conversions.

SEE ALSO

yodlstriproff(1), yodl(1), yodlconverters(1), yodlletter(7), yodlmacros(7), yodlmanpage(7), yodlpost(1), yodlverbinsert(1).

BUGS
--

AUTHOR

Frank B. Brokken (f.b.brokken@rug.nl),