Recently we inherited several big boxes (about 1 cubic meter!) of LEGO from the neighbor's boys downstairs. Playing LEGO with my kids got me back into it's powerful design space. When you ask good software designers about childhood influences they usually name two factors: LEGO and set theory (new math).

Some twenty years ago Peter Glaser was among the first who wrote [1,2] about the connection between LEGO and programming. He called it "Hirn-LEGO" which translates to "Brain-LEGO". I always thought "Gedanken-LEGO", as in Gedanken experiment, was more appropriate.

To me Lisp is the LEGO of programming languages:

• Both were invented during the 1950s.
• As the basic building material the list resembles the classic 8 stud brick of LEGO.
• The REPL makes programming as interactive as plugging red bricks onto the green baseplate.
• No syntactic sugar, just plug and play.
• Nothing is glued together forever. Anything can be changed even at runtime.
• You can use macros to add new specialized bricks to your vocabulary.

References:
[1] Glaser, Peter: [Chaos CD][HaBi 1]- Das BASIC-Gefühl - Vom Leben mit einem MicroComputer, 1985
[2] Glaser, Peter: The BASIC Feeling or Life with a (Micro) Computer, 1985
[3] Halfbakery: Lego Programming
[4] Forth - the LEGO of Programming Languages