Algorithm of J. M. Borwein and P. B. Borwein for computation of
Pi number starts with the initializations
X=SQRT(2); Pi=2+X; Y=SQRT(X)
and then repeats the iteration
X = 0.5 * (SQRT(X) + 1 / SQRT(X)
Pi = Pi * (X + 1) / (Y + 1)
Y = Y * (SQRT(X) + 1 / SQRT(X)) / (Y + 1)

IMPLEMENTATION
Unit: internal function, external function without procedure statement
Interface: SQRT function
Parameter: a positive integer P  number of digits of Pi, implicit P=9
Returns: the first P significant decimal digits of Pi, default is 9
PI: procedure
parse arg P
if P = "" then P = 9; numeric digits P
X = SQRT(2, P); Pi = 2 + X
Y = SQRT(X, P); X = Y
do forever
X = 0.5 * (X + 1 / X)
NewPi = Pi * (X + 1) / (Y + 1)
if Pi = NewPi then return Pi
Pi = NewPi
X = SQRT(X, P)
Y = (Y * X + 1 / X) / (Y + 1)
end

There is an another way to obtain the value of the number
Pi: we can compute the number
Pi only once and save its value into the text of the function. The following
PICONST function can be used to computing of the first
P decimal digits of
Pi, for
P=1,...,200. It was created automatically by the program, see
Technique: Beforehand computed constants.
PICONST: procedure; V = ''
V = V  3.14159265358979323846264338327950288419
V = V  7169399375105820974944592307816406286208
V = V  9986280348253421170679821480865132823066
V = V  4709384460955058223172535940812848111745
V = V  028410270193852110555964462294895493038196
return V

The statement Number_Pi=PI(1000) computes 10 times loop in PI function and requires 79 seconds.
CONNECTIONS