English Idiom in Unix: Directory Recursively

[Steven W. Orr]

On 5/17/2011 6:26 PM, Xah Lee wrote:
> might be of interest.
>
> 〈English Idiom in Unix: Directory Recursively〉
> http://xahlee.org/comp/idiom_directory_recursively.html

The answer is from compute science 101. From any standard data structures 
course, you learn the algorithm for how to walk a tree. To make it simple, the 
example is to use a binary tree which means that any non-leaf node of a tree may 
only have two child nodes, which are designated as Left and Right. There are 
only three things that are possible: Visit, Go Left, or Go Right. This means 
that a tree traversal program can only be written three ways:
A PreOrder Traversal will Visit, Go Left, Go Right.
An InOrder Traversal will Go Left, Visit, Go Right.
A PostOrder Traversal will Go Left, Go Right, Visit.

So, the Visit function is the function that does whatever you want to have 
happen at that node. Selection of whether you want to do things like copy, print 
or delete are designated by what kind of traversal you perform. And, since the 
Traversal function calls itself, it is, by definition, recursive.

QED.

-- 
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