The newbie feeling

I read a blog post:http://blog.recursivity.com/post/9204470867/the-problem-with-the-scala-community that triggered me to write this post.

I do not know the Scala community so I can not agree or disagree with the conclusion:

“I love the Scala community and the eco-system around the language, but quite frankly, to foster the continued growth of the community, we need to call out the small minority of bullies on their bullshit whenever it occurs: being able to confuse and intellectually intimidate newbies to the language and community is not proving your supposed “intellectual superiority”, it is merely a reflection of an insecure ego and social incompetence.”

I do think that as a person we can not know everything of everything and even if we could one moment in time the world will change and we have to learn the new thing.

So we have two option: stick with what we know or accept the newbie feeling.

When you are a newbie you will make mistakes. My grant parents had the following text on a tile:”The only man who never makes mistakes is the man who never does anything.” I just found out it is a quote from Theodore Roosevelt (thanks Google).

So if we want to progress we have to accept the newbie feeling, accept the insecurity and make mistakes.

When we want to progress we have several options, one option is to learn it all by yourself, another is to accept the support of the community.

The community can support you in two ways:

• one is provide knowledge
• the other to provide mentorship

I think a programming language community is able to provide knowledge, that is nature of the community. To provide mentorship is something else and it is very hard to provide it on line.

So as a newbie look for knowledge on line and find mentorship somewhere else.

The difference between SelectMany and Select in LINQ

This is follow up on my previous blog post:Adding xml strings in C# using LINQ.

In the previous post I showed that LINQ can be used to to manipulate XElements and strings. LINQ managed the transformation between the classes.

XElement result =
  from x1 in el1
  from x2 in el2
  select x1.Substring(0, x1.LastIndexOf("<")) + x2.Substring(x2.IndexOf(">") + 1);

el1, el2 and the result are XElements and x1, x2 and the object before select are strings.

In the example there are two XElements and the compiler requires that we implement SelectMany. If delete SelectMany we get the following error:

In case we have one XElement we expect that the following will compile:

private static XElement ToUpper(XElement el)
{
  XElement result =
  from x in el
  select x.ToUpper();

  return result;
}

It does not: “'System.Xml.Linq.XElement' does not contain a definition for 'Select'”

So we implement Select:

public static XElement Select(this XElement el, Func<string, XElement> f)
{
  return SelectMany(el, f, (x, y) => y);
}

Again it does not compile: “Cannot implicitly convert type 'string' to 'System.Xml.Linq.XElement'”

So we add an extra conversion:

private static XElement ToUpper(XElement el)
{
  XElement result =
  from x in el
  select XElement.Parse(x.ToUpper());

  return result;
}

This time it works:

var el = XElement.Parse("<a><b>1</b><b>2</b></a>");
Console.WriteLine(string.Format("ToUpper: {0}", ToUpper(el)));

Results in:

as expected.

Another way to solve the issue is to add a dummy line and use SelectMany:

private static XElement ToUpper(XElement el)
{
  XElement result =
  from x in el
  from dummy in XElement.Parse("<dummy></dummy>")
  select x.ToUpper();

  return result;
}

with the same result.

Update: more information at: http://msdn.microsoft.com/en-us/library/bb546168.aspx

Adding xml strings in C# using LINQ

This is follow up on my previous blog post:Adding xml strings in F# using computation expressions. The text is nearly identical, the language is C# instead of F#.

In some cases classes are enhanced wrappers of simple classes. For instance in .NET:

• DateTime is a point in time and provides, among others things, extra functionality related to representing date and time formats.
• XElement is an xml string and provides, among others things, checks to determine the validity of the xml string.
• Option can contain a value and can tell you if there is value available.

Sometimes you have to deal with underling class and reuse some of the functionality of the wrapper. In this case you could consider using LINQ. We first define the Return, Bind and SelectMany functions to create the required functions.

For details more details see:

• Functional Programming in C#: Classic Programming Techniques for Modern Projects (Wrox Programmer to Programmer)
• Real World Functional Programming: With Examples in F# and C#
• Monads in C#–1. Introduction

All excellent resources.

public static classXmlMonad
{
  //monad
 public staticXElement Return(this stringtext)
  {
    try
   {
      returnXElement.Parse(text);
    }
    catch(XmlException exc)
    {
      returnXElement.Parse(String.Format("<XmlException>{0}</XmlException>", exc.Message));
    }
  }

  public staticXElement Bind(thisXElement el, Func<string, XElement> f)
  {
    try
   {
      returnf(el.ToString());
    }
    catch(XmlException exc)
    {
      returnXElement.Parse(String.Format("<XmlException>{0}</XmlException>", exc.Message));
    }
  }

  public staticXElement SelectMany(thisXElement el, Func<string, XElement> f, Func<string, string, string> select)
  {
    returnel.Bind(text => f(text).Bind(x => select(text, x).Return()));
  }
}

We can now define a add function that will xml elements by using a string manipulation:

private static XElement Add(XElement el1, XElement el2)
{
  XElement result =
  from x1 in el1
  from x2 in el2
  select x1.Substring(0, x1.LastIndexOf("<")) + x2.Substring(x2.IndexOf(">") + 1);

  return result;
}

Add in action:

var el1 = XElement.Parse("<a><b>1</b><b>2</b></a>");
var el2 = XElement.Parse("<a><b>3</b><b>4</b></a>");

Console.WriteLine(string.Format("Add: {0}", Add(el1,el2)));

Results in:

When we change the xml into:

var el2 = XElement.Parse("<c><b>3</b><b>4</b></c>");

The result is:

Adding xml strings in F# using computation expressions

In some cases types are enhanced wrappers of simple types. For instance in .NET:

• DateTime is a point in time and provides, among others things, extra functionality related to representing date and time formats.
• XElement is an xml string and provides, among others things, checks to determine the validity of the xml string.
• Option can contain a value and can tell you if there is value available.

Sometimes you have to deal with underling type and reuse some of the functionality of the wrapper. In this case you could consider using computation expressions.

This is a simple xml example. We create a xmlBuilder and reuse the validation logic of XElement:

open System
open System.Xml
open System.Xml.Linq

type xmlBuilder()=
    member x.Bind(el:XElement,(f:string -> XElement)) =
        try
            f(el.ToString())
        with
            | :? XmlException as exc -> XElement.Parse(String.Format("<XmlException>{0}</XmlException>", exc.Message))
    member x.Return(text) = 
        try
            XElement.Parse(text)
        with
            | :? XmlException as exc -> XElement.Parse(String.Format("<XmlException>{0}</XmlException>", exc.Message))

The string “123” creates an error:

let xml = new xmlBuilder()

let error =
    xml { 
            return "123"
        }

val error : XElement = <XmlException>Data at the root level is invalid. Line 1, position 1.</XmlException>

The expression can now be used to reuse sting functions:

let toUpper el =
    xml { 
            let! x = el
            return x.ToUpper()
        }

let el = XElement.Parse("<a><b>1</b><b>2</b></a>")
let result1 = el |> toUpper 

val result1 : XElement = <A>
  <B>1</B>
  <B>2</B>
</A>

In the same way we can define a simple add function for xml:

let (+) (el1:XElement) (el2:XElement) =
    xml { 
            let! x1 = el1
            let! x2 = el2
            return x1.Substring(0, x1.LastIndexOf("<")) + x2.Substring(x2.IndexOf(">") + 1)
        }

let el1 = XElement.Parse("<a><b>1</b><b>2</b></a>")
let el2 = XElement.Parse("<a><b>3</b><b>4</b></a>")
let result2 = el1 + el2

val result2 : XElement =
  <a>
  <b>1</b>
  <b>2</b>
  <b>3</b>
  <b>4</b>
</a>

let el3 = XElement.Parse("<c><b>3</b><b>4</b></c>")
let result3 = el1 + el3

val result3 : XElement = <XmlException>The 'a' start tag on line 1 position 2 does not match the end tag of 'c'. Line 7, position 3.</XmlException>

This may not be in line with the concept of information hiding, but it can help you in case you have to deal with the simple type to get the work done.