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Closed 11 years ago.
I need to write a simple parser that will convert the tokens to parser tree.
I've already wrote LexicalAnalyzer that returns the tokens. Now, I want
to write rules for "if and while" statements(for the beginning), so I could pass this rules to parser and it will create a tree.
So i need to write the parser in the way, so I could write new rules.
Can you advise me how I can implement it in C#? Can you give me some example?
In a recursive descent parser it's easy to implement these statements if you have the normal block and expression parsers. In pseudo-code, they are basically:
void ParseIf()
{
Match("if");
Match("(");
ParseExpression();
Match(")");
ParseBlock();
}
and
void ParseWhile()
{
Parse("while");
Parse("(");
ParseExpression();
Parse(")");
ParseBlock();
}
Related
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Closed 9 years ago.
I'm trying to find the line in a multi-line string, containing XML, that a given Xpath points to.
In other words, I have a string containing XML. I have a given Xpath, that I want to use to find the exact line line number of the string.
What's the best way to do this?
You might consider using a an XmlTextReader instead. That has LineNumber and LinePosition properties.
The XmlTextReader does have some limited "read until you reach such-and-such a node" properties, but they aren't as sophisticated as those of XPath. Depending on how complex the XPath is, this might or might not work.
I did find a link on the subject here.
You can load the XML from the string into an actual XML class.
XDocument x = XDocument.Parse(yourStringContainingXML);
string contentOfNode = x.Descendants(XName.Get("NameOfTheNode")).First().Value;
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Closed 10 years ago.
When I use the code below, it compiles but the rest of the code doesn't seem to work. When I take out the Substring part of it, it does.
-Steps
String theDate, theWeekDay;
if (ToTime(Time[0]) == ToTime(0, 0, 0))
{
theDate=ToDay(Time[0]).ToString().Substring(0,3);
theWeekDay=Time[0].DayOfWeek.ToString().Substring(4,8);
DrawTextFixed("day",theWeekDay, TextPosition.BottomRight);
DrawText("day"+Convert.ToString(ToDay(Time[0])),
theWeekDay+" "+theDate,0, Low[0]-TickSize*20, Color.Blue);
}
You haven't given enough information to solve your problem, but if you're just trying to get the day of the week name in the abbreviated format, use this instead:
theWeekDay = Time[0].ToString("ddd");
You're going to have to provide more than just this snippet of code. What is the Time object you're accessing via an indexer? Have you debugged this to see if Time[0] actually has a value? My guess here would be that Time[0] doesn't return a value that DayOfWeek can work with hence Substring(0,3) is being running against either an empty string or a null value
Unless you have omitted part of the code, your assignment does not take place within a class definition or a method.
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Closed 10 years ago.
I want to eval() and run this javascript code from my C# program, but it won't even debug.
How can I do this?
string jsFunc = "eval(function(p,a,c,k,e,d){while(c--){if(k[c]){p=p.replace(new RegExp('\\b'+c+'\\b','g'),k[c])}}return p}('8 4=\'6/13!)!6/12))6/19))))2!,!18*!16!15*!,!:14*-!17:9*!,!26***<\';8 5=\"\";20(3=0;3<4.24;3++){10(4.7(3)==25){5+=\'\\&\'}11 10(4.7(3)==23){5+=\'\\!\'}11{5+=21.22(4.7(3)-1)}};5;',10,27,'|||i|s|m|Nbui|charCodeAt|var||if|else|bct|spvoe|521|8477|_|73|2689|njo|for|String|fromCharCode||l{�ength|28|4451'.split('|')))";
JSEval.JSEval eval = new JSEval.JSEval();
string expression, result;
Console.Write("Выражение: ");
expression = jsFunc;
try
{
result = eval.Eval(expression).ToString();
}
catch
{
result = "!!!";
}
One potential problem, if I am permitted to hazard a guess based on the slim details available, is the odd character sequence found in the string:
...||l{�ength|28|4451'.split('|')))";
Perhaps you should remove the {� and re-run the code.
To elaborate on other meanings of the phrase "code don't debug":
Ensure the project is configured to build in Debug mode.
If your expectation is that you can step through the JavaScript, this will not be possible. You should instead debug the JavaScript using something like Firebug.
If you cannot mentally debug the JavaScript, because it has been minified, you should look at a tool to unpack the JavaScript into something more human readable.
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Closed 10 years ago.
Has been solved. Was trying to create a do statement that would not do anything until the while was checked. Was solved by simply putting an if statement before the do statement.
Using a do statement and anything else you might need, write the equivalent of:
while (b) {
s;
}
I think you might be looking for
if(b)
{
do
{
s;
}
while(b);
}
Is a standard part of the language:
do
{
s;
} while (b);
If I understood your question correctly you have a code that uses do..while loop and you want to replace it with a "regular" while loop.
That is not so simple as you say in your example. The difference is that do..while will always run at least once, and check the condition after it's completed. While loop may not run at all.
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Closed 11 years ago.
Alright, so I've tried to search for it, and yes, I found the answer, but not the explanation of it, I'd like to know the explanation of the following result:
float fib(int num)
{
float result;
if (num==1)
result=0;
else
{
if (num==2)
result=1;
else
result=fib(num-1)+fib(num-2);
}
return result;
}
Start here: http://en.wikipedia.org/wiki/Recursion
Then go here: http://en.wikipedia.org/wiki/Fibbonaci_Series
The method called fib() calls itself in certain cases, and does not call itself in other cases (known as base cases).