🚀 go-pugleaf

Ken Kahn writes:
>  To my way of thinking it is perhaps the
>most natural of the bunch.  Namely, write or use something that will generate
>a list of numbers and then multiply them together.  This is the APL-style of
>doing factorial.

In ISETL, another programming language that they use a lot in education, 
you say

	factorial := {x -> % * [1..x]}

E.g., "assign to the variable factorial the following value: a function that
maps x to the answer you get by reducing the list of numbers from 1 to x by
multiplying them all together."

You could do something like this in any language with first-class
functions.  (Or even LOGO, which merely has RUN and dynamic scope.)

TO ONETO :X
IF :X = 0 [OUTPUT []]
OUTPUT SE ONETO :X-1 :X
END

TO REDUCE :SENT :OP
IF EMPTYP BF :SENT [OP FIRST :SENT]
OUTPUT RUN (SE :OP FIRST :SENT REDUCE BF :SENT :OP)
END

TO FACTORIAL :N
OP REDUCE ONETO :N "PRODUCT
END

-Matt