Microsoft提出将Rolsyn API作为带有公共API的C＃编译器的实现。它为每个编译器管道阶段包含单独的API：语法分析，符号创建，绑定，MSIL发出。您可以提供自己的语法解析器实现或扩展现有的语法解析器实现，以便获得具有所需功能的C＃编译器。
让我们使用Roslyn扩展C＃语言！在我的示例中，我将替换带有相应的do-while的do-until语句：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Roslyn.Compilers.CSharp;
namespace RoslynTest
{
class Program
{
static void Main(string[] args)
{
var code = @"
using System;
class Program {
public void My() {
var i = 5;
do {
Console.WriteLine(""hello world"");
i++;
}
until (i > 10);
}
}
";
//Parsing input code into a SynaxTree object.
var SyntaxTree = SyntaxTree.ParseCompilationUnit(code);
var SyntaxRoot = SyntaxTree.GetRoot();
//Here we will keep all nodes to replace
var replaceDictionary = new Dictionary<DoStatementSyntax, DoStatementSyntax>();
//Looking for do-until statements in all descendant nodes
foreach (var doStatement in SyntaxRoot.DescendantNodes().OfType<DoStatementSyntax>())
{
//Until token is treated as an identifier by C# compiler. It doesn't kNow that in our case it is a keyword.
var untilNode = doStatement.Condition.ChildNodes().OfType<IdentifierNameSyntax>().FirstOrDefault((_node =>
{
return _node.Identifier.ValueText == "until";
}));
//Condition is treated as an argument list
var conditionNode = doStatement.Condition.ChildNodes().OfType<ArgumentListSyntax>().FirstOrDefault();
if (untilNode != null && conditionNode != null)
{
//Let's replace identifier w/ correct while keyword and condition
var whileNode = Syntax.ParseToken("while");
var condition = Syntax.ParseExpression("(!" + conditionNode.GetFullText() + ")");
var newDoStatement = doStatement.WithWhileKeyword(whileNode).WithCondition(condition);
//Accumulating all replacements
replaceDictionary.Add(doStatement, newDoStatement);
}
}
SyntaxRoot = SyntaxRoot.ReplaceNodes(replaceDictionary.Keys, (node1, node2) => replaceDictionary[node1]);
//Output preprocessed code
Console.WriteLine(SyntaxRoot.GetFullText());
}
}
}
///////////
//OUTPUT://
///////////
// using System;
// class Program {
// public void My() {
// var i = 5;
// do {
// Console.WriteLine("hello world");
// i++;
// }
//while(!(i > 10));
// }
// }
现在，我们可以使用Roslyn API编译更新的语法树，或将语法Root.GetFullText（）保存到文本文件并将其传递给csc.exe。
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