Artem's blog

Mainly .NET (C#, ASP.NET) and my projects

Archives for Complex operations using simple methods

Creating a programming language with Mathos Parser (2)

In this article, I would like to find out whether it is possible to construct a programming language with Mathos Parser. In general, the question is if a simple expression parser has the necessary things to easily convert it into a language.

The answer is yes, but the language will be very limited if additional features are not added. The reason for this is because what most languages have in common is some sort of  user/machine interaction, while an expression parser only allows you to parse mathematical things and is not really designed to interpret how to write to a file or allocate memory.

For example, imagine you want to create something similar to if statements  and you decide to treat an if as a function. You would use following code:

So, if whatever we pass into the first parameter is true, the value in the second parameter will be returned. This is quite cool, but it does not allow us to return a series of statements. Instead, we could design a new kind of if statement that would, depending on the result from this if function, execute the right method. Here is how I solved it:

As you can see, the if statement is still there, but there is now a feature that will interpret the result and make something happen. You can also use \n to separate between different statements and also name a collection of statements, as shown below:

Note that both examples use a function get(). It can also be implemented as a function:

You might have noticed the use of statements (see notTrue statement). Their role is to simulate a method. Everything you enter into a statement will not be executed until you call it, so you can insert undefined variables into a statement when you define it and later assign them with a value. I have also added commands like write, title, pause, clear and end. These are extensions to the language and are interpreted in the method below:

Some programmers will certainly argue that the code above is not that optimized and is quite primitive. Well, it serves its purpose and makes Mathos Parser look more like a language.

In the next article I want to implement a while feature into this awesome programming language.

Conclusion: Just because something can parse expressions does not mean it can parse a series of statement. In order to fix this we can either choose to add some features externally, or, go into the parser itself and make it more adjusted to this particular task. This language does not alter Mathos Parser in any way.


Factorial notation in Mathos Parser (1)

In this article series, I would like to look at how Mathos Parser (a very simple expression parser) can be used to perform things that were not originally intended. Today, I am going to show what has to be done to make Mathos Parser able to interpret factorial notation, such as “4!

Already in the parser, we can solve this in at least two different ways:

  • creating a localFunction fact() that will take one parameter and return the factorial of that number
  • using FactorialPower(falling power) instead, that is 4!4 would be 24 and 4!1=4.

Both methods do not require you to change anything in the input string, but they might not be as close to the mathematical notation as we want it to be. Therefore, as a part of this article, I am going to illustrate the changes in the input string that have to be made, to make it understand 4!.

  1. Include Reg Ex name space as following:
  2. Add these two methods somewhere in the class:
  3. Define the Mathos Parser and add a definition of the factorial operator including the way it should be executed. Note, at this stage, for this to work, the factorial number has to be in the form of 4!0 or 4!1 ((both result in 24).
  4. Before the input string can be parsed, perform the following action (assuming you have defined a variable input with a value):
  5. Parser the string and store the result:

This is how we can make Mathos Parser able to understand mathematical notation of factorial. In the next article of this series, we are going to look at how Mathos Parser can be used to construct a new programming language.