Debugging by Thinking

3.3 The methods of Lord Peter Wimsey 35

3.3

The books noted as anthologies contain twenty-one short stories about

Lord Peter and some about other characters of Dorothy L. Sayers's inven-

tion. The other works are complete novels. The last two novels were com-

pleted by completed by Jill Paton Walsh based on material from Sayers.

Ian Carmichael starred in video versions of five of the Lord Peter adven-

tures. These were originally aired in the United Kingdom and subsequently

in the United States on PBS's Masterpiece Theater. Edward Petherbridge

starred in video versions of three other Lord Peter Mysteries, which were

aired first on the BBC and later on PBS's Mystery? series. Both of these

series have recently become available on videocassette and DVD.

3.2.3 The author behind Lord Peter Wimsey

Dorothy L. Sayers was born in Oxford, England, in 1893, the daughter of a

clergyman. She was fluent in Latin, French, and German and was one of

the first women to earn an Oxford degree in 1915. She was a scholar of

medieval literature. After World War I, she worked for the largest British

advertising firm. In 1926, she married the famous World War I correspon-

dent, Capt. O. A. Fleming. After writing the last Lord Peter novel, she

spent the rest of her life translating medieval literature and writing plays

and academic studies. She died in 1957.

There are a couple of important points to observe about Dorothy L.

Sayers. She was educated at Oxford, a scholar of history and of literature.

Despite her academic training, she was capable of earning her living first in

the business world and later as a writer. In these respects, the detective that

she created was made in her own image.

The methods of Lord Peter Wimsey

We can summarize the points of Lord Peter's methodology that apply to

software debugging under the following categories:

9 Use alibis as clues

9 Eliminate impossible causes

9 Exercise curiosity

9 Reason based on facts

9 Enumerate possibilities

I Chapter 3

36 3.3 The methods of Lord Peter Wimsey

3.3.1

9 Use the power of logic

9 Use a system for organizing facts

9 Exercise caution when searching

9 Use gestalt understanding

9 Show how something could be done

Applying Wimsey to debugging

Once again, we apply the analogy of viewing software defects as crimes to

be solved. We must answer the following questions:

9 Who did it?~suspect

[] How did the culprit do it?~means

[] When did the culprit do it?~opportunity

3.3.2

Our approach to motive is somewhat different, since we assume that all

defects were caused accidentally, as we explained previously. We are inter-

ested in an answer to the question, why did this problem happen? We treat

the why question the way an accident investigator would, rather than the

way a detective would. The detective seeks to assign guilt for a crime. The

investigator seeks to find contributing causes, to prevent the accident from

occurring again.

Use alibis as clues

In

Have His Carcase

[Sa32], Lord Peter works with the mystery writer Har-

riet Vane. They search for the murderer responsible for a body Harriet

found on a beach while on holiday. After a serious investigation, Lord Peter

works his way through a long chain of deductions while conversing with

one of the suspects:

"Always suspect the man with the cast-iron alibi"~was not that the

very first axiom in the detective's book of rules? And here it was~the

cast-iron alibi which really was cast-iron; meant to be scrutinized;

meant to stand every test~as how should it not, for it was truth!