Problem #71: Rearranging Code ->

[David Wagle]

The problem is: 

The -> macro threads an expression x through a variable number of forms. First, x is inserted as the second item in the first form, making a list of it if it is not a list already. Then the first form is inserted as the second item in the second form, making a list of that form if necessary. This process continues for all the forms. Using -> can sometimes make your code more readable.

(= (__ (sort (rest (reverse [2 5 4 1 3 6]))))   (-> [2 5 4 1 3 6] (reverse) (rest) (sort) (__))   5)

Can someone put this description into an understandable format? They all look like English words, but I have no idea what the heck they mean in this context. 

Can someone explain what "->" does in a simpler fashion? 

[Bill Allen]

The easiest way to think about it is from left to right the result of the previous operation becomes the parameter to the next.

In this case the list [2 5 4 1 3 6] gets inserted as the parameter of reverse. The result of that is inserted as parameter of rest and so on. This is generally thought of as more readable than the traditional nested lisp style.

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[David Wagle]

Oh, ok. tthat’s much easier to understand. Thanks!

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