Thomas S. "Tom" Christiansen (born February 13, 1963), nicknamed tchrist or occasionally thoth, is a

Unix Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

developer and user known for his work with the

Perl Perl is a high-level, general-purpose, interpreted, dynamic programming language. Though Perl is not officially an acronym, there are various backronyms in use, including "Practical Extraction and Reporting Language". Perl was developed ...

programming language. Christiansen worked for several years at TSR Hobbies before attending the

University of Wisconsin - Madison A university () is an institution of tertiary education and research which awards academic degrees in several academic disciplines. ''University'' is derived from the Latin phrase , which roughly means "community of teachers and scholars". Univ ...

where he earned

B.A. A Bachelor of Arts (abbreviated B.A., BA, A.B. or AB; from the Latin ', ', or ') is the holder of a bachelor's degree awarded for an undergraduate program in the liberal arts, or, in some cases, other disciplines. A Bachelor of Arts degree ...

's in Spanish and Computer Science, and an

M.S. A Master of Science (; abbreviated MS, M.S., MSc, M.Sc., SM, S.M., ScM or Sc.M.) is a master's degree. In contrast to the Master of Arts degree, the Master of Science degree is typically granted for studies in sciences, engineering and medicine ...

in Computer Science. He worked for five years at

Convex Computer Convex Computer Corporation was a company that developed, manufactured and marketed vector minisupercomputers and supercomputers for small-to-medium-sized businesses. Their later Exemplar series of parallel computing machines were based on the He ...

. In 1993, he established the Tom Christiansen Perl Consultancy, located in

Lake Geneva, Wisconsin Lake Geneva is a city in the U.S. state of Wisconsin. Located in Walworth County and situated on Geneva Lake, it was home to 8,277 people as of the 2020 census, up from 7,651 at the 2010 census. It is located southwest of Milwaukee and no ...

. In 2010, he joined the Biomedical Text Mining Group at the University of Colorado School of Medicine. Christiansen, with a C- and-Unix background, was one of the early contributors to Perl after its public release in 1987. He presented the first public Perl tutorial in 1989 and wrote the first academic paper to highlight Perl in 1990. He was the author of much of the core Perl documentation, including the manual pages perlfaq and perltoot, development of ''perl.com''. In 1996, Christiansen wrote "''Csh Programming Considered Harmful''" about the limitations inherent in

C Shell The C shell (csh or the improved version, tcsh) is a Unix shell created by Bill Joy while he was a graduate student at University of California, Berkeley in the late 1970s. It has been widely distributed, beginning with the 2BSD release of the ...

Programming. Books he co-authored include: *The second (1996) and third (2000) editions of ''

Programming Perl ''Programming Perl'', best known as the Camel Book among programmers, is a book about writing programs using the Perl programming language, revised as several editions (1991–2012) to reflect major language changes since Perl version 4. Editions ...

''. *The second (1997) edition of ''

Learning Perl ''Learning Perl'', also known as the llama book, is a tutorial book for the Perl programming language, and is published by O'Reilly Media. The first edition (1993) was authored solely by Randal L. Schwartz, and covered Perl 4. All subsequent editi ...

'' (and its spin-off '' Learning Perl on Win32 Systems''). *'' The Perl Cookbook'' (1998). In 1999, Christiansen was one of the original recipients of the

White Camel award The Perl Foundation (TPF) is a non-profit, 501(c)(3) organization based in Holland, Michigan. It is dedicated to the advancement of the Perl and Raku programming languages through open discussion, collaboration, design, and code. The Perl Found ...

s from

Perl Mongers Perl Mongers is an international association of user groups for the Perl programming language, and part of The Perl Foundation. It was created as a stand-alone organization in 1998 by brian d foy and others, who formed the first group, the New ...

for his contribution to Perl's documentation. Christiansen has been called a "UNIX luminary". The common phrase "Only perl can parse Perl" is attributed to Tom Christiansen. It is not inspired by "Only tex can understand

TeX Tex, TeX, TEX, may refer to: People and fictional characters * Tex (nickname), a list of people and fictional characters with the nickname * Tex Earnhardt (1930–2020), U.S. businessman * Joe Tex (1933–1982), stage name of American soul singer ...

", but rather refers to Perl's unique capability, akin to a typedef or a #define in C or C++, where it can modify its syntactic rules dynamically while running. This empowers Perl to alter how its parser interprets code during execution, much like a type declaration changes the parsing process in C.

Randal Schwartz Randal L. Schwartz (born November 22, 1961), also known as merlyn, is an American author, system administrator and programming consultant. He has written several books on the Perl programming language, and plays a promotional role within the Per ...

also credits him with accidentally naming the

Schwartzian Transform In computer programming, the Schwartzian transform is a technique used to improve the efficiency of sorting a list of items. This idiom is appropriate for comparison-based sorting when the ordering is actually based on the ordering of a certain p ...

for optimizing some types of sorts. This happened after Schwartz used it in a

Usenet Usenet (), a portmanteau of User's Network, is a worldwide distributed discussion system available on computers. It was developed from the general-purpose UUCP, Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Elli ...

message, and Christiansen replied to the message giving some corrections and in one place said "the Schwartzian transform" to refer to the transform that Schwartz used.

References

External links

* (1999
"Plural of Virus"
* perl.co

* UNIX faq - shel
"Csh Programming Considered Harmful"
* (1991
"GUIs Considered Harmful"

PerlMonks ''PerlMonks'' is a community website covering all aspects of Perl programming and other related topics such as web applications and system administration. It is often referred to by users as 'The Monastery'. The name PerlMonks, and the general styl ...

* (1997
Interview with Tom Christiansen and Larry Wall
Web Review magazine, Feb 28, 1997 issue (link to archived copy) * (2009

{{DEFAULTSORT:Christiansen, Tom 1963 births Living people Perl writers O'Reilly writers University of Wisconsin–Madison College of Letters and Science alumni