Programming Into a Language: Great Examples

Question

In reference to Steve McConnell's Code Complete and its reference to "Programming into a language" versus "Programming in a language" (see this blog entry by Jon Skeet if you don't have the book handy), I would like to know your favorite/best examples of where you programmed into a language. I'll include my own for good measure.

Answer 1

My current favorite example of this is for VB/ASP.NET web projects. I hate massive "if" statements in the page load and then trying to figure out the logic on postbacks. Therefore, I have created a convention to separate code that loads on first requests, post backs, and a section for both. Applying this to all aspx.vb files helps me keep sane regarding this. I put this code in even if the subs are empty, as it makes it extremely easy to alter the code later.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If IsPostBack Then
        handlePostBack(sender, e)
    Else
        handleFirstTimeHere(sender, e)
    End If

    ' do this regardless

End Sub

Private Sub handlePostBack(ByVal sender As Object, ByVal e As System.EventArgs)
    ' stuff to do on postbacks
End Sub

Private Sub handleFirstTimeHere(ByVal sender As Object, ByVal e As System.EventArgs)
    ' stuff to do on non postbacks
End Sub

Answer 2

I recently had to implement (as a proof of concept) a finite state machine in RPG II. This isn't a natural match (to say the least) but by doing exactly what McConnell suggests, the code was reasonably straight forward:

C*
C*            Factor 1  Op   Factor 2  Result           Comments
C*
C* -----------State 0 --------------------------------------------
C*
C             STATE     IFEQ 0
C             CURCHAR   CASLT'0'       REJECT
C             CURCHAR   CASGT'9'       REJECT
C                       CAS            STATE=1
C                       END
C                       ELSE
C*
C* -----------State 1 --------------------------------------------
C*
C             STATE     IFEQ 1
C             CURCHAR   CASLT'.'       STATE=2
C             CURCHAR   CASLT'0'       ACCEPT
C             CURCHAR   CASGT'9'       ACCEPT
C                       END
C                       ELSE
C*
C* -----------State 2 --------------------------------------------
C*
C             STATE     IFEQ 2
C             CURCHAR   CASLT'0'       REJECT
C             CURCHAR   CASGT'9'       REJECT
C                       CAS            STATE=3
C                       END
C                       ELSE
C*
C* -----------State 3 --------------------------------------------
C*
C             STATE     IFEQ 3
C             CURCHAR   CASLT'0'       ACCEPT
C             CURCHAR   CASGT'9'       ACCEPT
C                       END
C                       ELSE
C*
C* ----------------------------------------------------------------
C*
C                       END                             End for state 3
C                       END                             End for state 2
C                       END                             End for state 1
C                       END                             End for state 0
C*
C* ----------------------------------------------------------------
C*
C             STATE=1   BEGSR
C                       Z-ADD1         STATE
C                       ENDSR
C*
C             STATE=2   BEGSR
C                       Z-ADD2         STATE
C                       ENDSR
C*
C             STATE=3   BEGSR
C                       Z-ADD3         STATE
C                       ENDSR
C*
C             ACCEPT    BEGSR
C                       ENDSR
C*
C             REJECT    BEGSR
C                       ENDSR

The key was breaking the problem into two parts: figure out what you want to express, and then figure out how best to express it in the target language. I fear a pure RPG II style solution would have been an utter mess.

Answer 3

I missed the concepts of Blocks (from Smalltalk) in Java and went through a phase where I did something like this (this general type of back in JDK 1.1, updated for generics):

interface Block<T>
{
    void perform(T data);
}

public class Main
{
    public static void main(final String[] argv)
    {
        final ForEach<Integer> each;
        final List<Integer>    values;

        each   = new ForEach<Integer>();
        values = new ArrayList<Integer>();
        each.iterate(values,
                     new Block<Integer>()
                     {
                        public void perform(final Integer data)
                        {
                            System.out.println(data);
                        }
        });
    }
}

class ForEach<T>
{
    public void iterate(final Iterable<T> values,
                        final Block<T>      block)
    {
        for(final T value : values)
        {
            block.perform(value);
        }
    }
}

Answer 4

This is probably one of the most useless things I've programmed, but here it is:

This is a documented, unit tested PHP implementation of Ruby's Enumerable mixin. All methods (except .entries and .to_set) listed here are implemented: ruby-doc.org::Enumerable

The motivation for doing this came from this StackOverflow question, "How can I use PHP closures like ruby blocks?". This class emulates ruby blocks using anonymous functions, and it's more a proof of concept than anything else.

Source code and examples available here.