Virtual CloneDrive

Virtual CloneDrive is a convenient CD image mounter that masquerades as a permanent device.

Alan Kay's Definition of OOP

From Meaning of "Object-Oriented Programming" According to Dr. Alan Kay:

OOP to me means only messaging, local retention and protection and hiding of state-process, and extreme late-binding of all things. It can be done in Smalltalk and in LISP. There are possibly other systems in which this is possible, but I'm not aware of them.

This was written in 2003, long after the creation of C++ or Java.

MACLISP

The old MACLISP manual is now available on-line in revised form as The Pitmanual.

PXSL

Parsimonious XML Shorthand Language (PXSL) is interesting both for what it does (provide a shorthand syntax for XML) and for how it is implemented (in Haskell).

SQL Server 2000 Functions vs. Usefulness

The SQL Server 2000 development team have really gone out of their way to make table-valued functions less than useful.  Here, for example, is a function that will retrieve ancestors of a row in some kind of hierarchy table:

create function ancestors(@id int)
returns @t table(id int)
as begin
  while 1=1 begin
    select @id=(select parentId from hierarchyTable where id=@id)
  if @id is null break
    insert into @t values(@id)
  end
  return
end

But don't actually try to use this function:

select a.id, anc.id from hierarchyTable a
left join ancestors(a.id) anc on (1=1)

The alias 'a' is not visible in the argument to the function call.  In fact, it appears that the only way to pass a non-constant value to a table-valued function is within a stored procedure.

Apparently, this is fixed in SQL Server 2005 using the new CROSS APPLY or OUTER APPLY join operators.  Of course, SQL Server 2005 implements recursive queries using the WITH clause for SELECT statements, so such function shenanigans are less necessary:

WITH

  data AS (
    SELECT 'grandparent' AS id, CAST(NULL AS VARCHAR(MAX)) AS parent
    UNION SELECT 'parent 1', 'grandparent'
    UNION SELECT 'parent 2', 'grandparent'
    UNION SELECT 'child 1', 'parent 1'
    UNION SELECT 'child 2', 'parent 1'
    UNION SELECT 'child 3', 'parent 2'
    UNION SELECT 'child 4', 'parent 2'
  )

, hierarchy AS (
    SELECT 0 AS level, CAST(NULL AS VARCHAR(MAX)) AS parent, id
    FROM data
    WHERE parent IS NULL
    UNION ALL
    SELECT parent.level+1, child.parent, child.id
    FROM data AS child
    INNER JOIN hierarchy AS parent ON parent.id = child.parent
  )

SELECT * from hierarchy
ORDER BY 1, 2, 3

Parnas on Software Engineering

In a similar vein, some of David Parnas' lectures concerning software engineering can be found at the David Parnas Lecture Series at the University of Limerick.

PDFCreator

For the record, here is a link to the PDFCreator Windows printer driver on pdfforge.

Early LISP Paper

John McCarthy has put one of his seminal LISP papers up on the web as HTML: Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I.