Syntax10.Scn.Fnt
FoldElems
Syntax10.Scn.Fnt
This is a short demo that shows the use of fold elements.
a) Middle-click at a filled triangle (e.g. behind the procedure Insert). The procedure body is shown.
	Middle-click at the non-filled triangle. The procedure body is collapsed again.
b) Expand procedure Insert and then its local procedure Ins. You find two pseudocode actions that can also be expanded.
c) Make a new fold element by selecting some text and executing FoldElems.Insert
d) Compile this file with
		FoldComp.Compile */s
	A (deliberate) error is reported. Set the caret at the beginning of the text and execute
		FoldComp.ShowError .
	The error location is revealed and marked with a small rectangle. middle-click at it to get the error message.
e) FoldElems.Expand expands all elements. FoldElems.Collapse collapses them all.
Syntax10i.Scn.Fnt
Syntax10.Scn.Fnt
	VAR s: Texts.Scanner;
BEGIN
	Texts.OpenScanner(s, Oberon.Par.text, Oberon.Par.pos); Texts.Scan(s);
	IF s.class = Texts.Name THEN COPY(s.s, n) ELSE n := "" END
END GetName;
Syntax10.Scn.Fnt
FoldElems
Syntax10.Scn.Fnt
FoldElems
Syntax10.Scn.Fnt
FoldElems
Syntax10.Scn.Fnt
GraphicElems
Alloc
Rectangles
Syntax10.Scn.Fnt
father
Syntax10i.Scn.Fnt
p := tree; father := NIL;
		WHILE p # NIL DO
			IF elem.name = p.name THEN RETURN END;
			father := p;
			IF elem.name < p.name THEN p := p.left ELSE p := p.right END
		END;	
see picture
Syntax10i.Scn.Fnt
Syntax10.Scn.Fnt
IF father = NIL THEN tree := elem
		ELSIF elem.name < father.name THEN father.left := elem
		ELSE father.right := elem
		END
		VAR p, father: Node;
	BEGIN elem.left := NIL; elem.right := NIL;
find insertion place (father)
insert elem under father
	END Ins;
	VAR x: Node;
	PROCEDURE Ins(elem: Node);	
BEGIN
	NEW(x); GetName(x.name); Ins(x)
END Insert;
Syntax10.Scn.Fnt
FoldElems
Syntax10.Scn.Fnt
	BEGIN
		IF x # NIL THEN
			P(x.left); Texts.WriteString(w, x.name); Texts.WriteLn(w); P(x.right)
		END
	END P;
	PROCEDURE P(x: Node);	
BEGIN
	P(tree); Texts.Append(Oberon.Log, w.buf)
END Print;
Syntax10.Scn.Fnt
FoldElems
Syntax10.Scn.Fnt
		VAR p, x, y, father: Node;
	BEGIN
		p := tree; father := NIL;
		WHILE (p # NIL) & (name # p.name) DO
			father := p;
			IF name < p.name THEN p := p.left ELSE p := p.right END
		END;
		IF p # NIL THEN
			IF p.right = NIL THEN x := p.left
			ELSIF p.right.left = NIL THEN x := p.right; x.left := p.left
			ELSE
				x := p.right; WHILE x.left # NIL DO y := x; x := x.left END;
				y.left := x.right;
				x.left := p.left; x.right := p.right
			END;
			IF father = NIL THEN tree := x
			ELSIF name < father.name THEN father.left := x 
			ELSE father.right := x 
			END
		END
	END Del;
	VAR name: Name;
	PROCEDURE Del(name: Name);	
BEGIN
	GetName(name); Del(name);
END Delete;
read me
MODULE FoldDemo;
IMPORT Oberon, Texts;
	Name = ARRAY 32 OF CHAR;
	Node = POINTER TO NodeDesc;
	NodeDesc = RECORD
		name: Name;
		left, right: Node
	END;
VAR tree: Node; w: Texts.Writer;
PROCEDURE GetName(VAR n: Name);	
PROCEDURE Insert*;	
PROCEDURE Print*;	
PROCEDURE Delete*;	
BEGIN tree := NIL; Texts.OpenWriter(w)
END FoldDemo.