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HELP SHOWTREE                                   J L Cunningham, Nov 1982
                                           Revised John Gibson, Aug 1993

------------------------------ NOTE ------------------------------------

  From Version 14.5, a change has been made to LIB SHOWTREE which makes
  it incompatible with previous versions: the new version has all the
  exported (i.e. top-level) identifiers prefixed by "showtree_" (except
  for showtree itself).

  The old identifier names can be got by loading LIB * OLD_SHOWTREE,
  which requires LIB * POPOBSOLETELIB first, i.e.

        uses popobsoletelib, old_showtree;

  This file describes the new names; the relationship between old and
  new is fairly obvious (but see LIB * OLD_SHOWTREE if in any doubt).


    uses showtree;


         CONTENTS - (Use <ENTER> g to access required sections)


-- SHOWTREE ------------------------------------------------------------

This library provides a procedure -showtree- which takes a tree, by
default represented as lists within lists, (an example of these are the
parse trees produced by LIB * GRAMMAR), and draws it on the screen using
VED. It is normally called from outside VED, although it is okay to call
it inside VED.  You can also call it from Prolog: see the end of this


    uses showtree;
    showtree([alpha [beta gamma] [delta [epsilon]]]);

Tree nodes are either atoms, or heads of sublists.  Atoms are not drawn
in a box, heads of sub-lists are drawn in a box.  Details of how to
extend this are given below.

-- SHOWTREE_MESS -------------------------------------------------------

The procedure -showtree_mess- does the same as -showtree- but adds a
message helpful to non-VED users above the displayed tree.

-- SHOWTREE_PRINTABLE and SHOWTREE_GRAPHICAL ---------------------------

On most VDUs the tree displayed on the screen uses symbols that cannot
be printed on a line-printer.  If you call the procedure


then the characters used to draw the tree will be suitable for printing.
This procedure also alters -showtree_vgap- to have the value 5.
WARNING: if the tree is too wide to fit on the printer paper, it will
not be nice.


will make showtree use the characters used before -showtree_printable-
was called.  -showtree_vgap- is set to be 4.

-- PROCEDURES AND VARIABLES --------------------------------------------

A number of procedures and variables are available to be used, or
re-defined, by the user to allow easy extensions of the facilities in
this library.

Also available are a number of variables whose values are vedfileprops
(see * NEWVEDFILEPROP) containing PROPERTIES; these give information
about positions of nodes in the layout etc.  For more information look
at the library file.

showtree_box(column1, line1, column2, line2)                 [procedure]
        Draw a box whose top left  position is line1, column1 and  whose
        bottom right position is line2, column2.

showtree_daughters(subtree)                                  [procedure]
        Should return a list of the immediate subtrees of this  subtree.
        The default values is -tl-.

showtree_draw_node(node, position)                           [procedure]
        Used to draw the  node -node- at  position given by  -position-.
        -position- is node_location(node).

showtree_height(node, name)                                  [procedure]
        Returns the number of lines used to show the given node.

showtree_isleaf(node)                                        [procedure]
        Used to determines whether a node is printed in a box. If a node
        is a leaf,  it is not  printed in a  box, but is  printed as  PR
        prints it. The default value of -showtree_isleaf- is * ATOM.

showtree_name_&_subtrees(tree) -> name -> subtrees;          [procedure]
        If a subtree is not a leaf  node, its root node will be  printed
        in a  box,  in  which case  the  (user  re-definable)  procedure
        -showtree_name_&_subtrees- is  called. The  procedure takes  one
        argument and returns  two results:  It should return  a word  or
        string to be  used as the  node name  of the root  node of  this
        subtree, and  a  list (which  may  be  the empty  list)  of  the
        subtrees   immediately   below   this   node.   Note   that   if
        -showtree_isleaf- is true, then the node is a leaf of the  tree,
        but if it is  false, then the  node may still be  a leaf of  the
        tree in  the sense  that  it may  have  no daughter  nodes.  The
        default    value     for     -showtree_name_&_subtrees-     uses
        -showtree_root- and -showtree_daughters- (q.v.).

        The default value for -showtree_name_&_subtrees- assumes that if
        the  -showtree_root-   of   a   subtree   is   a   leaf   (using
        -showtree_isleaf- q.v.) then that is the name of its root  node,
        otherwise that the node is anonymous, and that the *DATALIST  of
        the subtree is the required list of DAUGHTERs.

showtree_node_daughters()(node)                            [vedfileprop]
        Returns a list of daughters of node.

showtree_node_draw_data()(node)                            [vedfileprop]
        Returns a list of the form [label startrow] where -label- is the
        name produced by -showtree_name_&_subtrees-  or the node  itself
        if the  node is  a leaf.  The label  can be  used by  draw_node.
        startrow is the first row on which the node is displayed.

showtree_node_location()(node)                             [vedfileprop]
        Returns a  list  of  the form  [startrow  finishrow  startcolumn
        finishcol] for the given node.

showtree_quit()                                              [procedure]
        Removes the tree file from the list of file being edited.

showtree_root(tree)                                          [procedure]
        Should return the  item to be  printed as the  name of the  root
        node. This will be converted  to a string if necessary.  Default
        value is -hd-.

showtree_defaults()                                          [procedure]
        Procedure used  when  calling  vededitor to  display  the  tree.
        Default is -vedhelpdefaults-.

showtree_init()                                              [procedure]
        Procedure called before the tree is planned (and may be used  to
        set  the  values  of  -showtree_isleaf-,  -showtree_root-  etc).
        Default value is -identfn-.

showtree_name                                                 [variable]
        The name of the file used to display the tree. The initial value
        is 'tree.t'.

showtree_subtree_rootnode_name()(subtree)                  [vedfileprop]
        Returns node name for given subtree. A property to give  inverse
        mapping from tree fragments to  node names. N.B. this will  only
        work on sub-trees, not on leafs.

showtree_graphical()                                         [procedure]
        Makes -showtree- use the  best graphic characters available  for
        the current vdu. See above.

showtree_printable()                                         [procedure]
        Makes -showtree- use characters  that can be  printed on a  line
        printer. See above.

showtree_vgap                                                 [variable]
        The minimum  number  of lines  beteen  nodes vertically.  It  is
        initially 1.

showtree_width(node, name)                                   [procedure]
        Returns the width that will be used to display node. By default,
        if the node  has daughters  then this will  be 2  more than  the
        length of name  (to allow for  a box) otherwise  it will be  the
        length of name.

$-showtree$-connectup()                                      [procedure]
        Draws the  connections between  the  nodes. Uses  the  procedure
        -drawline-    and    the    data     held    in    the     table

$-showtree$-shapetree(node)                                  [procedure]
        Updates the data held  in the table -showtree_node_location-  to
        reflect the correct layout of the tree.

$-showtree$-transformtree(tree, depth) -> topnode            [procedure]
        Involved in calculating the layout of the tree on the screen.

-- A SIMPLE EXAMPLE ----------------------------------------------------

Normally it will be unnecessary to redefine -showtree_name_&_subtrees-,
as it will be sufficient to redefine -showtree_isleaf-, -showtree_root-
and -showtree_daughters-. As an example:

    defclass bintree {value, left, right};

    vars tree;
    consbintree("top",consbintree("alpha",1,2),3) -> tree;

    isbintree <> not -> showtree_isleaf;
    value -> showtree_root;
    define showtree_daughters(tree);
        [% left(tree), right(tree) %]


-- A MORE COMPLICATED EXAMPLE ------------------------------------------

    define showtree_width(tree, name) -> w;
        lvars tree name i w = 0;
        if isvector(name) then
            for i from 1 to length(name) do
                max(length(name(i)), w) -> w
            w + 2 -> w
            length(name) -> w

    define showtree_height(tree, name);
        lvars tree name;
        if isvector(name) then
            length(name) + 2

    define showtree_draw_node(node,val);
        lvars node val i name;
        vars r1 r2 c1 c2;
        val --> [?r1 ?r2 ?c1 ?c2];
        hd(showtree_node_draw_data()(node)) -> name;
        if isvector(name) then
            showtree_box(c1, r1, c2-2, r2);
            c1 + 1 -> c1;
            r1 + 1 -> r1;
            for i from 1 to length(name) do
                vedjumpto(r1, c1);
                r1 + 1 -> r1;
            vedjumpto(r1+1, c1);

    define showtree_name_&_subtrees() -> name -> subtrees;
        lvars name,subtrees;
        destpair() -> subtrees -> name;

    showtree([{top} [above [{a fairly big node}
        {with a very tall sub node}]] and
        [{a} [deep [{sub tree} {which} {is} fairly {wide}]]]
        [also [{a smaller node} with {some 'sub-' nodes}]]]);

-- FROM PROLOG ---------------------------------------------------------
                                   Added 8 July 1983, Jonathan Laventhol

Almost everything written above applies when calling SHOWTREE from
Prolog, although of course you have to use prolog syntax (and the
prolog predicates use the old names without the showtree_ prefix).
This is just a list of the predicates that are available.

    ?- library(showtree).

    ?- showtree(Tree).

    ?- showtreemess(Tree).

    ?- vgap(X).         /* find value of vspacing */
    ?- vgap(6).         /* set value of vspacing */

    ?- tree_printable.
    ?- tree_graphical.


    Make a printable tree, with helpful message:

    ?- tree_printable.
    ?- showtreemess([alpha, [beta, gamma], [delta, [epsilon]]]).

--- C.all/help/showtree ------------------------------------------------
--- Copyright University of Sussex 1987. All rights reserved. ----------