Factorial in FP
Example for versions
Interactive FP
This example defines four functions — two of necessity, and two for readability. All of them accept scalar values for input; seq
returns a sequence of scalars, and the other three return individual scalars.

zero
checks whether its argument is equal to zero; 
dec
decrements its argument; 
seq
returns<0>
if its argumentx
is equal to zero, andseq
, applied to(x1)
, withx
appended to right otherwise (if we unwind this recursive definition, we’ll get simply the sequence of values<0 1 ... x>
). 
factorial
returns 1 if its argumentx
is equal to zero, andfactorial
, applied to(x1)
, multiplied byx
otherwise.
The last line of the example applies factorial
to each element of sequence, obtained by applying seq
to 16. Note that all math operations produce floating point values, so the actual output will look like this:
< 1 1.0 2.0 6.0 24.0 120.0 720.0 5040.0 40320.0 362880.0 3628800.0 3.99168E7 4.790016E8 6.2270208E9 8.7178289E10 1.30767428E12 2.09227885E13 >
{ zero ( = @ [id, %0] ) }
{ dec (  @ [id, %1] ) }
{ seq ( zero > %<0> ; apndr @ [ seq @ dec , id ] ) }
{ factorial ( zero > %1 ; * @ [id, factorial @ dec ] ) }
&factorial @ seq:16
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