(repeat-transformation #'(lambda (x) (* 2 x)) 4 1)
This is a LISP lambda function , i don't understand what is the last "1" ? Thanks.
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3 Answers
Definition: repeat-transformation (F N X)
Repeat applying function F on object X for N times.
You're defining your lambda function to be called by repeat-transformation 4 times on the integer 1.
Hope that explains it.
Comments
Google comes back with a recursive definition for repeat-transformation:
(defun repeat-transformation (F N X)
"Repeat applying function F on object X for N times."
(if (zerop N)
X
(repeat-transformation F (1- N) (funcall F X))))
Which indicates the 1 is the value on which the function operates. The next 3 Google links confirm it.
Comments
The lambda function is the first argument to repeat-transformation. 4 and 1 are the second and third arguments respectively.
The Lisp Tutorial Advanced Functional Programming in LISP defines a repeat-transformation function that repeats applying function F on object X for N times. If yours is equivalent, then the 1 is the number of times to apply the lambda function on the value 4.
2 Comments
dfan
Yes, it repeats applying F on X for N times, but the order of the arguments is F N X.
Terje Norderhaug
Good catch. It's a reminder to double-check the function signature rather than assume that the order of the arguments is the same as in the documentation string. It also demonstrates that it might be helpful to maintain the order of the arguments when documenting a function.