wiiki - AnonymousFunction

In a programming language, an unnamed function object (also: "function literal").

"lambda(x,y){ x>y }," is an anonymous function object representing the function that tells whether its first argument is greater than its second argument.

This lets you write (e.g.)

sort(lambda(x,y){ x>y },, [5,7,3,4,9,5,4])

instead of

def compfunc(x,y) {
  x>y
},

sort(compfunc,[5,7,3,4,9,5,4])

Analogously, "42" is an anonymous number object (or "number literal") representing the number 42, which lets you write (e.g.)

set_age(42)

instead of

def value := 42
set_age(value)

(for the last code snippet, imagine that this was written in a programming language that does not let you use numbers directly, but always requires you to give them a name first using "def <name> := <value>")

The syntax of anonymous functions depends on the programming language being used:

"lambda x,y: x>y" in PythonLanguage
"proc{|x,y|x>y}," in RubyLanguage
"{|x,y| x>y}," in FrinkLanguage
"sub { my ($x, $y) = @_; $x > $y }," in PerlLanguage
"(lambda (x y) (> x y))" in LispLanguage and SchemeLanguage
"function(x,y) {return x>y}," in JavaScript
"\x y -> x > y" in HaskellLanguage
"fun x y -> x > y" in ObjectiveCaml
"fn (x, y) => x > y" in SmlLanguage
"function($x, $y) { return $x > $y; }," in PhpLanguage 5.3+
"^(int x, int y) { return x > y; }," in ObjectiveCee (as well as CeeLanguage and CeePlusPlus) on MacOSX 10.6+
ForthLanguage: the execution token (xt) returned by ":noname ( x y -- ? ) > ;" (or simply " ' > " since operators are also functions)
[](int x, int y) { return x > y; }, in CeePlusPlusEleven
[:x :y | x > y] in SmallTalk
"OPERATOR (x INTEGER, y INTEGER) RETURNS BOOLEAN; RETURN x > y; END OPERATOR" in the RelProject. (Yes, it's verbose. Deliberately.)
"(x, y) => x > y" in CeeSharpLanguage
"(x, y) -> x > y" in JavaLanguage (Java 8 and above)

Shouldn't this be simply called an unnamed function? -- MarkJanssen

Sometimes it is. In every technical field, science or craft, some things get multiple names.