Book cover of Concrete Mathematics.
Xah Lee, 2002-02
Dear lispers,
The lambda character λ, always struck a awe in me, as with other mathematical symbols. In my mind, i imagine that those obscure math symbolism are etched in stone by god. A salient example is the book cover Concrete Mathematics by Ronald Graham et al. amazon
Book cover of Concrete Mathematics.
Here we see the summation sign ∑ etched in stone. The summation sign happens to be my favorite math symbol. (chosen as my website signet: 
)
These symbols are not to be trifled with. If anyone puffs in as much half a snicker, i wish god strikes a thunder upon their impudence.
The Greek lambda symbol is used in a branch of logic called lambda calculus. The theories of lambda calculus is what functional languages are based on, thus many functional language's logo feature the lambda. Here is a sampling:
MIT Scheme's logo features a recursive shield with lambda http://www.swiss.ai.mit.edu/projects/scheme/
Schemer.org's logo has a modernized look. It is a simple lambda inside a O figuration. http://www.schemers.org/ (the O figure is supposed to be a pair of parenthesis)
PLT Scheme logo, notable is the red/white/blue coloring scheme. http://www.plt-scheme.org/
MzScheme logo features a lambda besides a Chinese character 文 (wen2). The character means written language. http://www.plt-scheme.org/software/mzscheme/.
the Common Lisp HTTP server logo. http://www.ai.mit.edu/projects/iiip/doc/cl-http/home-page.html
Scheme shell scsh logo is a lambda inside a bivalve, perhaps most florid of the bunch: http://www.scsh.net/
Haskell language logo is a plain lambda: http://haskell.org/.
The Haskell interpreter Hugs98 features a 3D lambda with projected shadow http://www.haskell.org/hugs/
Yale Haskell project used a logo that features symbols in lambda calculus including the lambda, and also a bullfrog head. Quite funny and beautiful. (the bullfrog logo origin is explained at the bottom. i.e. that of parody to Yale's bulldog logo) http://web.archive.org/web/19990828153125/http://www.cs.yale.edu/haskell/yale-fp.html
The book cover of Structure and Interpretation of Computer Programs, by Harold Abelson, Gerald Jay Sussman, features a wizard and witch gesticulating with prominent lambda, and a monster foot of the table showing.
I love these lambda-featuring logos. However, i have a complaint. As most of you know, lisp languages are not purely functional languages. Subroutines in lisps easily have side-effects, and sometimes non-functional programing methodologies such as OOP are actually encouraged in lisp. As most of you know, the lambda symbol chosen by functional languages is to signify no side-effects. In this respect, i find the lisp languages not totally deserving the use of lambda in their logo. As i have expressed before, mathematical symbols are not to be trifled with, and the Schemers have tainted my mathematics, strictly speaking.
Although i have this minor objection with lispers using the lambda symbol, but overall i think the lispers and i share a more important common goal. That is, to kill all imperative programing ignoramuses of the world. Once the unix and C and Perl and otherwise idiots are all dead, then i'll formally raise my objection about Lisper's unfit borrowing of the lambda symbol.
(PS In America, imperative language programers are such not because they prefer such methodology, but because they know shit.)
Addendum, 2003-05, 2006-04, 2009-06.
Haskell language has a new logo, inaugurated in 2003-05. It is designed by Fritz Ruehr. Superb.
It is made of 5 math symbols revolving around a big lambda. The symbols are: right arrow →, inverted A ∀, double right-pointing angle bracket ≫, double colon ::, double right arrow ⇒, and lambda λ. The right arrow → signifies transformation. The inverted A ∀ signifies “for all”. The double angle ≫ signifies free from disorder. The double colon :: signifies exactitude. The double right arrow ⇒ signifies generality. Finally, the lambda λ signifies functionality.
PFP logo, by Martin Erwig.
The PFP library for Haskell features a lambda disguised as a histogram. One of the most well-designed among lambda logos. (“A Probabilistic Functional Programming Library for Haskell” by Martin Erwig and Steve Kollmansberger, 2005. http://web.engr.oregonstate.edu/~erwig/pfp/).
Logo for FC++ by Brian Dickens.
Someone has written a C++ library for functional programing, called FC++. (by Brian McNamara and Yannis Smaragdakis, 2003) Website: http://www.cc.gatech.edu/~yannis/fc++/index.html.
There's a Scheme-to-C compiler called Chicken, featuring a logo that is a lambda inside a hen silhouette. (by Felix L Winkelmann, at http://www.call-with-current-continuation.org/chicken.html).
This is getting silly and disrespectful.
Chicken's new logo. Left as of 2007-03, right as of 2009-06.
The Scheme compiler “Chicken” has a new logo, by Moe Aboulkheir et al. I prefer the original logo. This new “modern looking” logo lost it's chicken attraction. You can't easily tell what bird it is, and the funky lambda takes some tech geeking to recognize. The original logo of the fat hen signifies birth, with lambda right in its tummy. (For some detail about Chicken Scheme's logo, see http://galinha.ucpel.tche.br:8080/logos (accessed on 2007-12-19))
A Qi (programming language) logo designed by yours truely. For detail, see: Qi Language Logo.
Logo of Clojure, a new Lisp lang in Java Virtual Machine. The logo is designed by Tom Hickey with input from Rich Hickey. A SVG version is here: http://clojure.googlegroups.com/web/Clojure.svg.
Haskell has a new logo, again.
Haskell's new logo.
This logo's concept is based on ASCII art by Darrin Thompson, and interpreted by Jeff Wheeler. It is a result of public logo contest. For detail, and many quality logo entries, see Source.
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