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    <p>First of all, <a href="http://en.wikipedia.org/wiki/Lazy_evaluation" rel="nofollow noreferrer">lazy evaluation</a> wasn't invented in Haskell, it's incorrect to attribute it like so.</p> <p>Second, Haskell has eager evaluation (the opposite; evaluate when referred) possibilities too.</p> <p>Third, lazy evaluation facilities are easily available in other languages and technologies too; Python's generators (recall the <code>xrange</code> function), Meyers singleton and template instantiation in C++, delayed symbol resolution in runtime linkers -- are all examples of this idea.</p> <p>So anyway, accomodating that idea and corresponding vocabulary will never be harmful to a software engineer.</p> <p>As to the pros &amp; cons, you named the primary ones. There can be named a few more (remember, you can do these in virtually any language with data structures and function calls):</p> <ul> <li><p><a href="http://www.haskell.org/haskellwiki/Tying_the_Knot" rel="nofollow noreferrer"><strong>Recursive datastructures</strong></a>, where you can create, for example, a list value with elements arranged in a cirle, the head being the <code>next</code> element of the "last" one; traversing such a list would yield an infinitely repeating sequence of elements. Probably not the most motivating example, but you can do the same with trees, graphs and so on.</p></li> <li><p>Arranging <strong>control flow</strong> with lazy data structures instead of built-in primitives; think of building <a href="http://en.wikipedia.org/wiki/Coroutine" rel="nofollow noreferrer">coroutines</a> with just lazy lists. This is actually the other side of the coin of more complex and convoluted evaluation order (i.e. one of your <em>contra</em> being an advantage).</p></li> <li><p>Semi-<strong>automatic parallelisation</strong> of computations. This is more of the <a href="https://stackoverflow.com/questions/210835/what-is-referential-transparency">referential transparency</a>'s advantage rather than lazy evaluation; but still, the features fuse together very organically.</p></li> <li><p>Performance-wise, <strong><a href="http://en.wikipedia.org/wiki/Memoization" rel="nofollow noreferrer">memoization</a></strong> often comes to mind when musing on lazy evaluation; although doing it automatically is a hard (probably still unsolved) problem with lots of details and pitfalls.</p></li> </ul> <p>So, basically, if you look at it deeper, every aspect comes with possibilities and trade-offs; your task as a software engineer is to know all of these and choose wisely based on concrete problem details.</p>
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