@Section
  @Title { Objects }
  @Tag { objects }
@Begin
@PP
Since our aim is to produce neatly formatted documents, we should begin by
looking at a typical example of such a document:
@ID {
nohyphen @Break @LittleDocument
//
@LittleText {
@DP
|0.5rt {@B PURCELL}{ 0.8f @Font 1 ^//0.2v}
@LittleFootNote
{ { 0.8f @Font 1 ^//0.2v}Blom, Eric.  @I {Some Great Composers.}  Oxford, 1944.
}
@DP
In the world of music England is supposed to be a mere province.  If she
produces an indifferent composer or performer, that is regarded
elsewhere as perfectly normal and natural; but if foreign students of
musical history have to acknowledge a British musical genius, he is
considered a freak.
@PP
Such a freak is Henry Purcell.  Yet if we make a choice of fifteen of
the world's musical classics, as here, we find that we cannot omit this
English master.
}
//
@LittleEndRun
}
It is a large rectangle made from three smaller rectangles -- its
pages.  Each page is made of lines; each line is made of words,
although it makes sense for any rectangle (even a complete document) to
be part of a line, provided it is not too large.
@PP
Lout deals with something a little more complicated than rectangles:
@I objects.  An object
objec @Index { Object }
is a rectangle with at least one @I {column mark}
column.mark @Index { Column mark }
mark.alignment @Index { Mark alignment }
alignment @RawIndex { Alignment @I see mark alignment }
protruding above and below it, and at least one @I {row mark}
row.mark @Index { Row mark }
protruding to the left and right.  The simplest objects contain words like
metempsychosis, and have one mark of each type:
@ID {
@ShowMarks metempsychosis
}
The rectangle exactly encloses the word; its column mark is at the left
edge, and its row mark passes through the middle of the lower-case
letters.  The rectangle and marks do not appear on the printed page, but
to understand what Lout is doing you have to imagine them.
@PP
To place two objects side by side, we separate them by the
symbol @Code "|", which denotes the act of @I {horizontal
concatenation}.  So, if we write
@ID {
@Code "USA  |  Australia"
}
the result will be the object
@ID {
@ShowMarks USA | @ShowMarks Australia
}
Notice that this object has two column marks, but still only one row mark,
because @Code "|" merges the two row marks
together.  This merging of row marks fixes the vertical
position of each object with respect to the other, but it does not
determine how far apart they are.  This distance, or {@I gap},
may be given just after the symbol, as in @Code "|0.5i" for example,
which specifies horizontal concatenation with a gap of half an inch.  If
no gap is given, it is assumed to be {@Code "0i"}.
@PP
@I {Vertical concatenation} & , denoted by {@Code "/"},
is the same apart from the change of direction:
@ID {
@Code "Australia  /0.1i  USA"
}
has result
@ID {
@ShowMarks Australia /0.1i
@ShowMarks USA
}
The usual merging of marks occurs, and now the gap determines the
vertical separation.  Horizontal and vertical can be combined:
@ID  @Code {
             |1m  USA         |1m  "|0.2i" |1m   Australia
/1vx "/0.1i" |    Washington  |    "|"     |     Canberra
}
has result
@ID {
  @BackEnd @Case {
    PostScript @Yield {
      @ShowMarks USA &
      { 0 ymark moveto xsize 10 pt add ymark lineto [ 3 pt ] 0 setdash stroke }
      @Graphic {1c @Wide }
      |0.2i @ShowMarks Australia
/0.1i @ShowMarks Washington  |     @ShowMarks Canberra
    }
    PDF @Yield {
      @ShowMarks USA &
      { [ __mul(3, __pt) ] 0 d 0 __ymark m __add(__xsize, __mul(10, __pt)) __ymark l S }
      @Graphic {1c @Wide }
      |0.2i @ShowMarks Australia
/0.1i @ShowMarks Washington  |     @ShowMarks Canberra
    }
  }
}
tables @Index { Tables }
There are several things to note carefully here.  White space (including
tabs and newlines) adjacent to a concatenation symbol is ignored, so
it may be used to lay out the expression clearly.  The symbol
@Code "|" takes precedence over {@Code "/"}, which means that the rows
are formed first, then vertically concatenated.  The symbol @Code "/" will
merge two or more column marks, creating multiple
columns (and @Code "|" will merge two or more row marks).  This
implies that the gap @Code "0.2i" used above is between
columns, not individual items in columns; a gap in the second row
would therefore be redundant, and so is omitted.
@PP
A variant of @Code "/" called @Code "//" left-justifies
two objects instead of merging their marks.
@PP
By enclosing an object in braces, it is possible to override the
braces @Index { Braces }
set precedences.  Here is another expression for the table
above, in which the columns are formed first:
@ID  @Code {
             |1m "{ USA"       |1m "/0.1i" |1m "Washington }"
/1vx "|0.2i" |   "{ Australia" |   "/"     |   "Canberra }"
}
Braces have no effect other than to alter the grouping.
@PP
@I {Paragraph breaking} occurs when an object is too wide to fit
paragraph.breaking @Index { Paragraph breaking }
into the space available to it; by breaking its paragraphs into lines,
its width is reduced to an acceptable amount.  The available
space is determined by the @@Wide symbol, whose form is
@ID  {
@I length  @@Wide  @I object
}
and whose result is the given object modified to have exactly the given
length.  For example,
@ID @OneRow @Code {
"5i @Wide {"
"Macbeth was very ambitious.  This led him to wish to become king of"
"Scotland.  The witches told him that this wish of his would come true.  The"
"king of Scotland at this time was Duncan.  Encouraged by his wife, Macbeth"
"murdered Duncan.  He was thus enabled to succeed Duncan as king.  (51 words)"
"|0.5i"
"Encouraged by his wife, Macbeth achieved his ambition and realized the"
"prediction of the witches by murdering Duncan and becoming king of Scotland"
"in his place.  (26 words)"
"}"
}
has for its result the following five inch wide object
@Cite { $strunk1979style }:
@ID {
5i @Wide {
Macbeth was very ambitious.  This led him to wish to become king of
Scotland.  The witches told him that this wish of his would come true.  The
king of Scotland at this time was Duncan.  Encouraged by his wife, Macbeth
murdered Duncan.  He was thus enabled to succeed Duncan as king.  (51 words)
|0.5i
Encouraged by his wife, Macbeth achieved his ambition and realized the
prediction of the witches by murdering Duncan and becoming king of Scotland
in his place.  (26 words)
}
}
A paragraph of text can be included anywhere, and it will be broken
automatically if necessary to fit the available space.  The spaces
between words are converted into concatenation symbols.
@PP
These are the most significant of Lout's object-building symbols.  There
are others, for changing fonts, controlling paragraph breaking, printing
graphical objects like boxes and circles, and so on, but
they do not add anything new in principle.
@End @Section
