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The built-in macro <code>DEFINECHARTABLE</code> defines a character translation table.
It takes two parameter lists: the name of the table and the character
translations. Hence, each table is defined by its own name.

As an example of a table, consider the following fragment.  It defines a table
that translates the upper case characters <code>A</code> to <code>E</code> to their lower case
equivalents:

<pre>
DEFINECHARTABLE(tolower)(
    'A' = "a"
    'B' = "b"
    'C' = "c"
    'D' = "d"
    'E' = "e"
)
</pre>

<p>Each <code>DEFINECHARTABLE</code> statement <strong>must</strong> have a non-empty second
parameter. "Empty" character tables cannot be defined, though one
non-translation table is built-in.
<p>The syntaxis of the second parameter list is as follows:
<p><dl>
<p><li > On separate lines, input characters are mapped to a sequence to
    appear on the output.
<p><li > Per line, the input character is specified as <code>'c'</code>, <code>c</code> being
    any character. Escape-sequences from the <strong>C</strong> programming language can be
    used in this specification; Yodl supports the sequences <code>\a</code> (alert),
    <code>\b</code> (beep), <code>\f</code> (formfeed), <code>\n</code> (newline), <code>\r</code> (carriage
    return), <code>\t</code> (tab), and <code>\v</code> (vertical tab). Any other character
    following a \ defines itself: <code>\\</code> defines one backslash character. 
<p><li > Following the character specification, a <code>=</code> must appear.
<p><li > Following that, a sequence of one or more characters appears,
    enclosed in double quotes, defining the translation. Again, escape
    sequences can be used, as in:
<p><pre>
'\n' = "End of line\n"
</pre>

<p>Such a mapping adds the text <code>End of line</code> to each line, since each
    newline character in the input is replaced by the text <code>End of line</code>,
    followed by the newline itself.
<p></dl>
<p>Translations which are <strong>not</strong> specified in the table are left to the default,
which is to output the character as-is.
<p>Note that the character table translation is something that the <code>yodl</code>
program does as one of its last actions, just before sending text to the
output file. The expansion text is not further processed by <code>yodl</code>, except
for the conversion of <strong>C</strong>-type escape sequences to ordinary characters. The
expansion text should therefore not be protected by, e.g., <code>NOTRANS</code>
(unless of course you want some character to generate the text <code>NOTRANS</code>
on the output).
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Copyright (c) 1997, 1998, 1999 Karel Kubat and Jan Nieuwenhuizen.

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