Interpreter in VB.NET

   1:      ' Interpreter Design Pattern.

   2:      ' See description in //www.vb-net.com/ProgramTheory/Interpreter.htm

   3:      Class MainApp

   4:          ' Entry point into console application.

   5:          Public Shared Sub Main()

   6:              Dim context As New Context()

   7:              ' Usually a tree 

   8:              Dim list As New ArrayList()

   9:              ' Populate 'abstract syntax tree' 

  10:              list.Add(New TerminalExpression())

  11:              list.Add(New NonterminalExpression())

  12:              list.Add(New TerminalExpression())

  13:              list.Add(New TerminalExpression())

  14:              ' Interpret

  15:              For Each exp As AbstractExpression In list

  16:                  exp.Interpret(context)

  17:              Next

  18:              ' Wait for user

  19:              Console.ReadKey()

  20:          End Sub

  21:      End Class

  22:   

  23:      ' The 'Context' class

  24:      Class Context

  25:      End Class

  26:   

  27:      ' The 'AbstractExpression' abstract class

  28:      MustInherit Class AbstractExpression

  29:          Public MustOverride Sub Interpret(context As Context)

  30:      End Class

  31:   

  32:      ' The 'TerminalExpression' class

  33:      Class TerminalExpression

  34:          Inherits AbstractExpression

  35:          Public Overrides Sub Interpret(context As Context)

  36:              Console.WriteLine("Called Terminal.Interpret()")

  37:          End Sub

  38:      End Class

  39:   

  40:      ' The 'NonterminalExpression' class

  41:      Class NonterminalExpression

  42:          Inherits AbstractExpression

  43:          Public Overrides Sub Interpret(context As Context)

  44:              Console.WriteLine("Called Nonterminal.Interpret()")

  45:          End Sub

  46:      End Class