From: Alexander I. Baranovsky
Subject: Exceptions in VIRT, Freeware Interpreter Ver.2.0
Date: Sat, 21 Nov 1998 00:00:00 +0000
Message-ID: <ADIaZ6wW29@blast.donetsk.ua>

New version of the language VIRT ensures processing of exceptions
and errors handling. Now VIRT supports constructions such as try-except,
try-finally, on-do, raise. You can find the freeware VIRT interpreter
version 2.0 at the following URL : http://www.botspot.com/virt/

The mentioned above concepts are illustrated by a full source written
in VIRT ( file 'interp.w' ). It is interpreter for simple language with
gramma :

  Program    = "program"  { Statement } "end"
  Statement  = ( Assignment | Print ) ";"
  Print      = "print" Expression { "," Expression }
  Assignment = ID ":=" Expression
  Expression = Term   { ( "*" | "/" ) Term   }
  Term       = Factor { ( "+" | "-" ) Factor }
  Factor     = ID | "(" Expression ")" | - Factor | Number
  Number     = Digit { Digit }
  ID         = Letter { ( Letter | Digit ) }
  Digit      = "0"|"1"|..."9"
  Letter     = "a"|"b"|..."z"

Besides this demo source testifies that VIRT can be very attractive both for
interpreter writing and for the self-description.

As an example you can see a fragment of the file 'interp.w' below :

  object Scanner : TScanner
  object SymbolTable : TSymbolTable
  object Parser : TParser
  object Postfix : TPostfix

  P := 'program a3 := -78 * ( 6+11 ); b := a3 + 2; print a, b+4; and'
  writeln( P )

  Scanner.Init(  P, SymbolTable )
  SymbolTable.Init()
  PostFix.Init( SymbolTable )
  Parser.Init(  Scanner, Postfix )

  try
    Parser.Parse_PROGRAM()
  except
    on E : TFailrue do               -- TFailrue is user class
      E.ShowError()
      raise
    end
  end

  try
    try
      Postfix.Execute()
    except
      on E : TFailrue do
        E.ShowError()
      end
    end
  finally
    Postfix.Print()
    SymbolTable.Print()
  end

  return

Another demos are exposing the following VIRT applications : theorem
proving, processing of dynamic data structures, sorting, graph algorithmes,
numerical methods.

 Alexander I.Baranovsky
 E-mail : ·······@blast.donetsk.ua
 Flat 265, Constitution's square, 1
 Donetsk, Ukraine.
 Tel. 380622-371978