Helper method for defining space-delimited indentation blocks, such as
    those used to define block statements in Python source code.

    Parameters:
     - blockStatementExpr - expression defining syntax of statement that
            is repeated within the indented block
     - indentStack - list created by caller to manage indentation stack
            (multiple statementWithIndentedBlock expressions within a single grammar
            should share a common indentStack)
     - indent - boolean indicating whether block must be indented beyond the
            the current level; set to False for block of left-most statements
            (default=C{True})

    A valid block must contain at least one C{blockStatement}.

    Example::
        data = '''
        def A(z):
          A1
          B = 100
          G = A2
          A2
          A3
        B
        def BB(a,b,c):
          BB1
          def BBA():
            bba1
            bba2
            bba3
        C
        D
        def spam(x,y):
             def eggs(z):
                 pass
        '''


        indentStack = [1]
        stmt = Forward()

        identifier = Word(alphas, alphanums)
        funcDecl = ("def" + identifier + Group( "(" + Optional( delimitedList(identifier) ) + ")" ) + ":")
        func_body = indentedBlock(stmt, indentStack)
        funcDef = Group( funcDecl + func_body )

        rvalue = Forward()
        funcCall = Group(identifier + "(" + Optional(delimitedList(rvalue)) + ")")
        rvalue << (funcCall | identifier | Word(nums))
        assignment = Group(identifier + "=" + rvalue)
        stmt << ( funcDef | assignment | identifier )

        module_body = OneOrMore(stmt)

        parseTree = module_body.parseString(data)
        parseTree.pprint()
    prints::
        [['def',
          'A',
          ['(', 'z', ')'],
          ':',
          [['A1'], [['B', '=', '100']], [['G', '=', 'A2']], ['A2'], ['A3']]],
         'B',
         ['def',
          'BB',
          ['(', 'a', 'b', 'c', ')'],
          ':',
          [['BB1'], [['def', 'BBA', ['(', ')'], ':', [['bba1'], ['bba2'], ['bba3']]]]]],
         'C',
         'D',
         ['def',
          'spam',
          ['(', 'x', 'y', ')'],
          ':',
          [[['def', 'eggs', ['(', 'z', ')'], ':', [['pass']]]]]]]

def indentedBlock(blockStatementExpr, indentStack, indent=True):
    """
    Helper method for defining space-delimited indentation blocks, such as
    those used to define block statements in Python source code.

    Parameters:
     - blockStatementExpr - expression defining syntax of statement that
            is repeated within the indented block
     - indentStack - list created by caller to manage indentation stack
            (multiple statementWithIndentedBlock expressions within a single grammar
            should share a common indentStack)
     - indent - boolean indicating whether block must be indented beyond the
            the current level; set to False for block of left-most statements
            (default=C{True})

    A valid block must contain at least one C{blockStatement}.

    Example::
        data = '''
        def A(z):
          A1
          B = 100
          G = A2
          A2
          A3
        B
        def BB(a,b,c):
          BB1
          def BBA():
            bba1
            bba2
            bba3
        C
        D
        def spam(x,y):
             def eggs(z):
                 pass
        '''


        indentStack = [1]
        stmt = Forward()

        identifier = Word(alphas, alphanums)
        funcDecl = ("def" + identifier + Group( "(" + Optional( delimitedList(identifier) ) + ")" ) + ":")
        func_body = indentedBlock(stmt, indentStack)
        funcDef = Group( funcDecl + func_body )

        rvalue = Forward()
        funcCall = Group(identifier + "(" + Optional(delimitedList(rvalue)) + ")")
        rvalue << (funcCall | identifier | Word(nums))
        assignment = Group(identifier + "=" + rvalue)
        stmt << ( funcDef | assignment | identifier )

        module_body = OneOrMore(stmt)

        parseTree = module_body.parseString(data)
        parseTree.pprint()
    prints::
        [['def',
          'A',
          ['(', 'z', ')'],
          ':',
          [['A1'], [['B', '=', '100']], [['G', '=', 'A2']], ['A2'], ['A3']]],
         'B',
         ['def',
          'BB',
          ['(', 'a', 'b', 'c', ')'],
          ':',
          [['BB1'], [['def', 'BBA', ['(', ')'], ':', [['bba1'], ['bba2'], ['bba3']]]]]],
         'C',
         'D',
         ['def',
          'spam',
          ['(', 'x', 'y', ')'],
          ':',
          [[['def', 'eggs', ['(', 'z', ')'], ':', [['pass']]]]]]] 
    """
    def checkPeerIndent(s,l,t):
        if l >= len(s): return
        curCol = col(l,s)
        if curCol != indentStack[-1]:
            if curCol > indentStack[-1]:
                raise ParseFatalException(s,l,"illegal nesting")
            raise ParseException(s,l,"not a peer entry")

    def checkSubIndent(s,l,t):
        curCol = col(l,s)
        if curCol > indentStack[-1]:
            indentStack.append( curCol )
        else:
            raise ParseException(s,l,"not a subentry")

    def checkUnindent(s,l,t):
        if l >= len(s): return
        curCol = col(l,s)
        if not(indentStack and curCol < indentStack[-1] and curCol <= indentStack[-2]):
            raise ParseException(s,l,"not an unindent")
        indentStack.pop()

    NL = OneOrMore(LineEnd().setWhitespaceChars("\t ").suppress())
    INDENT = (Empty() + Empty().setParseAction(checkSubIndent)).setName('INDENT')
    PEER   = Empty().setParseAction(checkPeerIndent).setName('')
    UNDENT = Empty().setParseAction(checkUnindent).setName('UNINDENT')
    if indent:
        smExpr = Group( Optional(NL) +
            #~ FollowedBy(blockStatementExpr) +
            INDENT + (OneOrMore( PEER + Group(blockStatementExpr) + Optional(NL) )) + UNDENT)
    else:
        smExpr = Group( Optional(NL) +
            (OneOrMore( PEER + Group(blockStatementExpr) + Optional(NL) )) )
    blockStatementExpr.ignore(_bslash + LineEnd())
    return smExpr.setName('indented block')