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# Fork

A train of three verbs is a fork and is evaluated as follows:

      (f g h) y	evaluates as	(f y) g (h y)
    x (f g h) y	evaluates as	(x f y) g (x h y)

A simple example of a fork is the sequence of three verbs `+/ % #` . The `/` adverb takes its left argument `+` and returns a verb, so there is a sequence of three verbs. Let's examine the use of this fork monadically.

       (f  g h) y	evaluates as	(f  y) g (h y)
       (+/ % #) y	evaluates as	(+/ y) % (# y)

This can be read as: sum over the argument divided by the count of the argument. This is the definition of the mean or average.

       (+/ % #) 5 9 12
    8.66667

       (+/ % #) i.9
    4

You can now define mean as a fork with `+/ % #` .

       mean =. +/ % #
       mean i.9
    4

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