謝桂綱
10 years ago
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Imports System.CodeDom
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Imports System.Collections.Generic
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Imports System.Collections.Specialized
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Imports Microsoft.VisualBasic.Linq.Statements.TokenIcer
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Imports Microsoft.VisualBasic.Scripting.TokenIcer
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Namespace LDM.Parser
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''' <summary>
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''' Parses expressions written in strings into CodeDom expressions. There is a certain
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''' amount of context that the parser may need to be familiar with. This is why the
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''' parsing methods are not exposed as static.
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''' </summary>
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Public Class Parser : Implements System.IDisposable
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Private _Enums As Dictionary(Of String, CodeTypeReference) = New Dictionary(Of String, CodeTypeReference)
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Private _Fields As StringCollection = New StringCollection
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''' <summary>
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''' A collection of identifiers that should be recognized as enums.
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''' </summary>
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Public ReadOnly Property Enums() As Dictionary(Of String, CodeTypeReference)
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Get
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Return _Enums
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End Get
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End Property
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''' <summary>
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''' A collection of names of fields.
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''' </summary>
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Public ReadOnly Property Fields() As StringCollection
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Get
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Return _Fields
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End Get
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End Property
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''' <summary>
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''' Parses an expression into a <see cref="CodeExpression"/>.
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''' </summary>
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''' <param name="exp">expression to parse</param>
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''' <returns>CodeDom representing the expression</returns>
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Public Function ParseExpression(exp As Token(Of Tokens)()) As CodeExpression
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Return ReadExpression(exp, Scan0, TokenPriority.None)
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End Function
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''' <summary>
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''' Recursive method that reads an expression.
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''' </summary>
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''' <param name="t"></param>
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''' <param name="priority"></param>
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''' <returns></returns>
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Private Function ReadExpression(t As Token(Of Tokens)(), [next] As Integer, priority As TokenPriority) As CodeExpression
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Dim left As CodeExpression = Nothing, right As CodeExpression = Nothing
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Dim cont As Boolean = True, applyNot As Boolean = False, applyNegative As Boolean = False
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While cont
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Dim current As Token(Of Tokens) = t([next].MoveNext)
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Select Case current.TokenName
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Case Tokens.Float OrElse Tokens.Integer OrElse Tokens.String
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left = New CodePrimitiveExpression(current.TryCast)
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t.GetNextToken()
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cont = False
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Case TokenType.[Operator]
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' An operator here is considered a unary operator.
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Select Case t.Current.Text
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Case "-"
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applyNegative = True
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Case "!"
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applyNot = True
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Case Else
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Throw New Exception("Unexpected operator: " & t.Current.Text)
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End Select
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t.GetNextToken()
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Continue While
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Case TokenType.Identifier
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left = ReadIdentifier(t)
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cont = False
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Case TokenType.OpenParens
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t.GetNextToken()
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left = ReadExpression(t, TokenPriority.None)
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t.GetNextToken()
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If TypeOf left Is CodeTypeReferenceExpression Then
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left = New CodeCastExpression(TryCast(left, CodeTypeReferenceExpression).Type, ReadExpression(t, TokenPriority.None))
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End If
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cont = False
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End Select
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If t.IsInvalid Then
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cont = False
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End If
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End While
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If left Is Nothing Then
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Throw New Exception("No expression found.")
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End If
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If applyNot Then
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left = New CodeBinaryOperatorExpression(left, CodeBinaryOperatorType.ValueEquality, New CodePrimitiveExpression(False))
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ElseIf applyNegative Then
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left = New CodeBinaryOperatorExpression(New CodePrimitiveExpression(0), CodeBinaryOperatorType.Subtract, left)
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End If
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If t.IsInvalid OrElse t.Current.Type = TokenType.CloseParens OrElse t.Current.Type = TokenType.Comma OrElse t.Current.Type = TokenType.CloseBracket Then
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Return left
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End If
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cont = True
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While cont AndAlso Not t.IsInvalid
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Dim token As Token = t.Current
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Select Case token.Type
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Case TokenType.[Operator]
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If t.Current.Priority < priority Then
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cont = False
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Else
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' In the case we have an operator, we'll assume it's a binary operator.
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Dim binOp As CodeBinaryOperatorType
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Dim notEquals As Boolean = False
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Select Case token.Text
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Case ">"
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binOp = CodeBinaryOperatorType.GreaterThan
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Case ">="
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binOp = CodeBinaryOperatorType.GreaterThanOrEqual
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Case "<"
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binOp = CodeBinaryOperatorType.LessThan
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Case "<="
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binOp = CodeBinaryOperatorType.LessThanOrEqual
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Case "=", "=="
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binOp = CodeBinaryOperatorType.ValueEquality
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Case "!="
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binOp = CodeBinaryOperatorType.ValueEquality
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notEquals = True
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Case "|"
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binOp = CodeBinaryOperatorType.BitwiseOr
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Case "||"
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binOp = CodeBinaryOperatorType.BooleanOr
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Case "&"
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binOp = CodeBinaryOperatorType.BitwiseAnd
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Case "&&"
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binOp = CodeBinaryOperatorType.BooleanAnd
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Case "-"
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binOp = CodeBinaryOperatorType.Subtract
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Case "+"
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binOp = CodeBinaryOperatorType.Add
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Case "/"
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binOp = CodeBinaryOperatorType.Divide
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Case "%"
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binOp = CodeBinaryOperatorType.Modulus
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Case "*"
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binOp = CodeBinaryOperatorType.Multiply
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Case Else
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Throw New Exception("Unrecognized operator: " & t.Current.Text)
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End Select
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If t.IsInvalid Then
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Throw New Exception("Expected token for right side of binary expression.")
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End If
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t.GetNextToken()
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right = ReadExpression(t, token.Priority)
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left = New CodeBinaryOperatorExpression(left, binOp, right)
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' If the operator was the not equals operator, we just negate the previous binary expression.
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If notEquals Then
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left = New CodeBinaryOperatorExpression(left, binOp, New CodePrimitiveExpression(False))
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End If
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End If
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Case TokenType.CloseParens
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't.GetNextToken();
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cont = False
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Case TokenType.Dot
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' A dot could appear after some parentheses. In this case we need to parse
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' what's after the dot as an identifier.
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t.GetNextToken()
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right = ReadIdentifier(t)
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Dim ceTemp As CodeExpression = right
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While True
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If TypeOf ceTemp Is CodeVariableReferenceExpression Then
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left = New CodePropertyReferenceExpression(left, TryCast(ceTemp, CodeVariableReferenceExpression).VariableName)
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Exit While
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ElseIf TypeOf ceTemp Is CodePropertyReferenceExpression Then
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Dim cpre As CodePropertyReferenceExpression = TryCast(ceTemp, CodePropertyReferenceExpression)
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If TypeOf cpre.TargetObject Is CodeThisReferenceExpression Then
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cpre.TargetObject = left
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left = cpre
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Exit While
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Else
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ceTemp = cpre.TargetObject
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End If
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ElseIf TypeOf ceTemp Is CodeFieldReferenceExpression Then
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Dim cfre As CodeFieldReferenceExpression = TryCast(ceTemp, CodeFieldReferenceExpression)
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If TypeOf cfre.TargetObject Is CodeThisReferenceExpression Then
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cfre.TargetObject = left
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left = cfre
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Exit While
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End If
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ElseIf TypeOf ceTemp Is CodeMethodInvokeExpression Then
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Dim cmie As CodeMethodInvokeExpression = TryCast(ceTemp, CodeMethodInvokeExpression)
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If TypeOf cmie.Method.TargetObject Is CodeThisReferenceExpression Then
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cmie.Method.TargetObject = left
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left = cmie
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Exit While
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Else
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ceTemp = cmie.Method.TargetObject
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End If
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Else
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Throw New Exception("Unexpected identifier found after .")
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End If
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End While
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cont = False
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Case Else
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Throw New Exception("Token not expected: " & token.Text)
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End Select
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End While
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Return left
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End Function
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''' <summary>
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''' When an identifier is encountered, it could be a number of things. A single identifer by itself
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''' is considered a variable. The pattern identifier[.identifier]+ will consider the
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''' first identifier as a variable and the others as properties. Any identifier that is followed
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''' by an open parenthesis is considered to be a function call. Indexes are not handled yet, but
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''' should be handled in the future. If the identifier is "this" then a this reference is used.
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''' </summary>
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''' <param name="t"></param>
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''' <returns></returns>
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Private Function ReadIdentifier(t As Tokenizer) As CodeExpression
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Dim ce As CodeExpression = Nothing
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Dim token As Token = t.Current
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ce = New CodeVariableReferenceExpression(token.Text)
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token = t.GetNextToken()
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Return ce
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End Function
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#Region "IDisposable Support"
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Private disposedValue As Boolean ' 检测冗余的调用
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' IDisposable
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Protected Overridable Sub Dispose(disposing As Boolean)
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If Not Me.disposedValue Then
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If disposing Then
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' TODO: 释放托管状态(托管对象)。
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End If
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' TODO: 释放非托管资源(非托管对象)并重写下面的 Finalize()。
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' TODO: 将大型字段设置为 null。
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End If
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Me.disposedValue = True
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End Sub
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' TODO: 仅当上面的 Dispose(ByVal disposing As Boolean)具有释放非托管资源的代码时重写 Finalize()。
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'Protected Overrides Sub Finalize()
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' ' 不要更改此代码。 请将清理代码放入上面的 Dispose(ByVal disposing As Boolean)中。
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' Dispose(False)
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' MyBase.Finalize()
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'End Sub
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' Visual Basic 添加此代码是为了正确实现可处置模式。
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Public Sub Dispose() Implements IDisposable.Dispose
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' 不要更改此代码。 请将清理代码放入上面的 Dispose (disposing As Boolean)中。
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Dispose(True)
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GC.SuppressFinalize(Me)
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End Sub
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#End Region
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End Class
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End Namespace
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