In the J programming language, a fork is the special name given to a composite verb made by concatenating three verbs. The general format for a monadic fork follows (f and h are monadic, while g is dyadic, and v is some noun):

(f g h) v is identical to (f v) g (h v)

For example:

The concept of a fork also generalizes to dyadic verbs in a train:

x (f g h) v is identical to (x f v) g (x h v)

Again, an example:

The most important thing to note about the concept of a fork is that it allows extended chaining of verbs in a meaningful way, because a fork can also be a component of a fork (or a hook, which, as noted above, is just a special case of a fork).

For example, to find the distance of each element from the mean (an important step in finding the variance and standard deviation) we just do it:

(- +/ % #) v is
(] - (+/ % #)) v is
(] - (+/ % #)) v is
v - ((+/ % #) v) is
v - ((+/v) % (#v)) is
the pairwise subtraction of elements in v with their mean.

More information on extended chaining of J verbs can be found at train.