How to get a proper imathas link for a given mathematical expression string?

Question

For example for a string x + 1/y I want to generate this url with expression:

http://www.imathas.com/cgi-bin/mimetex.cgi?\displaystyle\blue{x}%2B\frac{{1}}{{y}}

Is there any tool doing this job in C#?

Answer 1

You could use the NCalc library to compile the mathematical expression x + 1/y into a imathas expression. The NCalc library creates an abstract syntax tree (AST) of a given mathematical expression string. You could then create a Visitor which transforms the AST into an imathas expression. For more information about the Visitor pattern please see the following wikipedia article.

The (incomplete) example below should give you a starting point:

// Implement a visitor
public class ImathasVisitor: LogicalExpressionVisitor
{
  // Result contains the imathas expression
  // after the visit.
  public StringBuilder Result = new StringBuilder();

  public override void Visit(Function function)
  {                
  }

  public override void Visit(LogicalExpression expression)
  {                
  }

  public override void Visit(TernaryExpression expression)
  {                
  }

  public override void Visit(UnaryExpression expression)
  {                
  }

  public override void Visit(Identifier identifier)
  {
    Result.AppendFormat("{{{0}}}", identifier.Name);
  }           

  public override void Visit(ValueExpression expression)
  {
    Result.AppendFormat("{{{0}}}", expression.Value);
  }

  public override void Visit(BinaryExpression expression)
  {                                
    switch(expression.Type)
    {
      case BinaryExpressionType.Div:
        Result.Append("\\frac{");
        expression.LeftExpression.Accept(this);
        Result.Append("}{");
        expression.RightExpression.Accept(this);
        Result.Append("}");
        break;
      case BinaryExpressionType.Plus:
        expression.LeftExpression.Accept(this);               
        Result.Append(HttpUtility.UrlEncode("+"));
        expression.RightExpression.Accept(this);                
        break;
      case BinaryExpressionType.Minus:
        expression.LeftExpression.Accept(this);               
        Result.Append("-");
        expression.RightExpression.Accept(this);                
        break;
    }                                                
  }           
}

static void Main(string[] args)
{
  // Create a NCalc expression.
  NCalc.Expression e = new NCalc.Expression("x + 1/y");

  // Check for syntax errors.
  if(e.HasErrors())
  {
    Console.Out.WriteLine("Syntax error.");
    return;
  }

  // Transform the parsed expression into
  // an imathas expression.
  ImathasVisitor iv = new ImathasVisitor();
  e.ParsedExpression.Accept(iv);

  Console.Out.WriteLine(iv.Result);
}

For a more elaborated example of a visitor the NCalc library comes with a build in SerializationVisitor which you definitely should have a look at.

Hope, this helps.