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<TITLE>3.2 Special Sequences</TITLE>
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<P><FONT SIZE="5">3.2 Special Sequences</FONT><BR>
<P>The scanner scans the input file from top to bottom,
left to right, treating the input as ordinary text (to be
handed directly to the parser as a text token) unless it
encounters the <STRONG>special character</STRONG> which
introduces a <STRONG>special sequence</STRONG>. Thus, the
scanner partitions the input file into ordinary text and
special sequences. (Note: This sort of character is often
referred to as the "escape character" or the
"control character" in other systems. However, as
there is great potential to confuse these names with the
"escape" character (ASCII 27) and ASCII
"control" characters, the term "special" has
been chosen instead. This results in the terms
<I>special character</I> and <I>special sequence</I> .
<P>
<PRE>
input_file = { ordinary_text | special_sequence }
</PRE>
<P>Upon startup, the special
character is
<SAMP>@</SAMP>, but it can be changed using the
<special><SAMP>=</SAMP><new_special> special sequence.
Rather than using <special> whenever the special
character appears, this document uses the default special
character "<TT>@</TT>" to represent the current special
character. More importantly, FunnelWeb's error messages all
use the default special character in examples,
even if the special character has been changed.
<P>An occurrence of the special character in the input
file introduces a special sequence. The kind of special
sequence is determined by the character following the
special character. Only printable characters can follow the
special character.
<P>The following list gives all the possible characters
that can follow the special character, and the legality of
each sequence. The first column gives the ASCII number of
each ASCII character. The second column gives the special
sequence for that character. The next column contains one of
three characters: "<TT>-</TT>" means that the sequence is
illegal. "<TT>S</TT>" indicates that the sequence is a
<STRONG>simple sequence</STRONG> (with no attributes or side
effects) that appears exactly as shown and is converted
directly into a token and fed to the parser. Finally,
"<TT>C</TT>" indicates that the special sequence is complex,
possibly having a following syntax or producing funny side
effects.
<P>
<PRE>
ASC SEQ COMMENT
-----------------
000 \
016 | Unprintable chars (illegal specials).
031 /
032 @ - Illegal (space).
033 @! C Comment.
034 @" S Parameter delimeter.
035 @# C Short name sequence.
036 @$ S Start of macro definition.
037 @% - Illegal.
038 @& - Illegal.
039 @' - Illegal.
040 @( S Open parameter list.
041 @) S Close parameter list.
042 @* - Illegal.
043 @+ C Insert newline.
044 @, S Parameter separator.
045 @- C Suppress end of line marker.
046 @. - Illegal.
047 @/ S Open or close emphasised text.
048 @0 - Illegal.
049 @1 S Formal parameter 1.
050 @2 S Formal parameter 2.
051 @3 S Formal parameter 3.
052 @4 S Formal parameter 4.
053 @5 S Formal parameter 5.
054 @6 S Formal parameter 6.
055 @7 S Formal parameter 7.
056 @8 S Formal parameter 8.
057 @9 S Formal parameter 9.
058 @: - Illegal.
059 @; - Illegal.
060 @< S Open macro name.
061 @= C Set special character.
062 @> S Close macro name.
063 @? - Illegal. Reserved for future use.
064 @@ C Insert special character into text.
065 @A S New section (level 1).
066 @B S New section (level 2).
067 @C S New section (level 3).
068 @D S New section (level 4).
069 @E S New section (level 5).
070 @F - Illegal.
071 @G - Illegal.
072 @H - Illegal.
073 @I C Include file.
074 @J - Illegal.
075 @K - Illegal.
076 @L S Macro is library macro.
077 @M S Macro may be called many times.
078 @N - Illegal.
079 @O S Macro is attached to product file.
080 @P C Pragma.
081 @Q - Illegal.
082 @R - Illegal.
083 @S - Illegal.
084 @T C Typesetter directive.
085 @U - Illegal.
086 @V - Illegal.
087 @W - Illegal.
088 @X - Illegal.
089 @Y - Illegal.
090 @Z S Macro may be called zero times.
091 @[ - Illegal. Reserved for future use.
092 @\ - Illegal.
093 @] - Illegal. Reserved for future use.
094 @^ C Insert control character into text
095 @_ - Illegal.
096 @` - Illegal.
097 @a \
109 @m | Identical to @A..@Z.
122 @z /
123 @{ S Open macro body/Open literal directive.
124 @| - Illegal.
125 @} S Close macro body/Close literal directive.
126 @~ - Illegal.
127 to 255 - Illegal specials (as non-standard ASCII).
</PRE>
<P>The most important thing to remember about the scanner
is that <I>nothing happens unless the special character
is seen.</I> There are no funny sequences that will cause
strange things to happen. The best way to view a FunnelWeb
document at the scanner level is as a body of text
punctuated by special sequences that serve to structure the
text at a higher level.
<P>The remaining description of the scanner consists of a
detailed description of the effect of each complex special
sequence.
<P>
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