public ICompilationUnitSyntax Parse(ITokenIterator <IEssentialToken> tokens)
{
var implicitNamespaceName = ParseImplicitNamespaceName(tokens);
var parser = new Parser(tokens, implicitNamespaceName);
var usingDirectives = parser.ParseUsingDirectives();
var declarations = parser.ParseNonMemberDeclarations <IEndOfFileToken>();
var eof = tokens.Required <IEndOfFileToken>();
var span = TextSpan.FromStartEnd(0, eof.End);
var diagnostics = tokens.Context.Diagnostics;
var compilationUnit = new CompilationUnitSyntax(implicitNamespaceName, span,
tokens.Context.File, usingDirectives,
declarations);
CheckSyntax(compilationUnit, diagnostics);
compilationUnit.Attach(diagnostics.Build());
return(compilationUnit);
}