できたー

IConnectable.boo

namespace ConsoleApplicationBoo

import System
import Boo.Lang.Compiler
import Boo.Lang.Compiler.Ast

interface IConnectable:
    def Open():
        pass
    
    def Close():
        pass

class ConnectMacro(AbstractAstMacro):
    override def Expand(macro as MacroStatement) as Statement:
        assert len(macro.Arguments) == 1
        connectableAssignExpression = macro.Arguments[0]
        
        openInvocationExpression = MethodInvocationExpression()
        openInvocationExpression.Target = MemberReferenceExpression(connectableAssignExpression, "Open")
        
        closeInvocationExpression = MethodInvocationExpression()
        closeInvocationExpression.Target = MemberReferenceExpression(connectableAssignExpression, "Close")
        
        tryStatement = TryStatement()
        tryStatement.ProtectedBlock = Block()
        tryStatement.ProtectedBlock.Add(openInvocationExpression)
        tryStatement.ProtectedBlock.Add(macro.Block)
        tryStatement.EnsureBlock = Block()
        tryStatement.EnsureBlock.Add(closeInvocationExpression)
        
        connectBlock = Block()
        connectBlock.Add(tryStatement)
        
        return connectBlock

Program.boo

namespace ConsoleApplicationBoo

import System

class HelloWorld(IConnectable):
    def Open():
        print "open"
    
    def Close():
        print "close"
    
    def Execute():
        print "Hello, World !"
    

connect con = HelloWorld():
    con.Execute()

Console.ReadLine()

で、ConnectMacro クラス書く代わりにこーやって簡単に書くことも可能、と。

macro Connect:
    assert len(Connect.Arguments) == 1
    return [|
        try:
            connectable as IConnectable = $(Connect.Arguments[0])
            connectable.Open()
            $(Connect.Block)
        ensure:
            connectable.Close()
    |]

こっちは簡単に記述できるけど、マクロ実行時 (＝コンパイル時) に検証を行わせたりすることはできない。・・・たぶんｗ
できたので検証処理追加しといた＾＾；