NB.  The fibonacci definitions.

fibonacci =: monad define
if. y. < 2
  do. y.
  else. (fibonacci y. - 1) + fibonacci y. - 2
end.
)

NB. a synonym for fibonacci

f =: fibonacci

fib_work =: monad define
if. y. < 2
  do. 1
  else. 1 + (fib_work y.-1) + fib_work y.-2
end.
)
fib_iter =: monad define
('a' ; 'b' ; 'count') =. y.
if. count = 0
  do. b
  else. fib_iter (a + b) , a , count - 1
end.
)

fibonacci1 =: monad def 'fib_iter 1 0 , y.'