Understand "curry" function

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cameyo
Posts: 108
Joined: Sun Mar 27, 2011 3:07 pm
Location: Italy

Understand "curry" function

Post by cameyo »

This is what I understand ...

I can map a function with multiple arguments in this way:

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(map pow '(2 1) '(3 4))
;-> (8 1)
where: 8 = 2^3, 1 = 1^4
But, if the list of arguments are within a list:

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(setq lst '((2 1) (3 4)))
I got an error:

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(map pow lst)
ERR: value expected in function pow : '(2 1)
I use "curry" to solve this problem:

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(map (curry apply pow) lst)
;-> (2 81)
where: 2 = 2^1, 81 = 3^4
Ok, transpose the list of arguments:

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(map (curry apply pow) (transpose lst))
;-> (8 1)
This is equivalent to:

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(map (lambda(x) (apply pow x)) (transpose lst))
;-> (8 1)
We can define a user function too:

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(define (mypow lst)
  (if (null? lst) '()
      (cons (pow (nth '(0 0) lst) (nth '(0 1) lst)) (mypow (rest lst)))
  )
)

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(setq lst '((2 1) (3 4)))
(mypow (transpose lst))
;-> (8 1)
Another example:

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(map max '(3 5) '(2 7))
;-> (3 7) 
(map (curry apply max) '((3 5) (2 7)))
;-> (5 7)
(map (curry apply max) (transpose '((3 5) (2 7))))
;-> (3 7)
Did I get it right?
cameyo
p.s. sorry for poor english...

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