Lazy Evaluation - Laziness in Eager Languages

Laziness in Eager Languages

Python

In Python 2.x the range function computes a list of integers (eager or immediate evaluation):

>>> r = range(10) >>> print r >>> print r 3

In Python 3.x the range function returns an iterator which computes elements of the list on demand (lazy or deferred evaluation):

>>> r = range(10) >>> print(r) range(0, 10) >>> print(r) 3
This change to lazy evaluation saves execution time for large ranges which may never be fully referenced and memory usage for large ranges where only one or a few elements are needed at any time.

Python manifests lazy evaluation by implementing iterators (lazy sequences) unlike tuple or list sequences. For instance:

>>> list = range(10) >>> iterator = iter(list) >>> print list >>> print iterator >>> print iterator.next 0
The above example shows that lists are evaluated when called, but in case of iterator, the first element '0' is printed when need arises.
This section requires expansion.

Read more about this topic:  Lazy Evaluation

Famous quotes containing the words laziness, eager and/or languages:

    “From passions grow opinions; intellectual laziness lets these harden into convictions.”
    —Friedrich Nietzsche (1844–1900)

    “I am grown by sympathy a little eager and sentimental, but leave me alone, and I should relish every hour and what it brought me, the pot-luck of the day, as heartily as the oldest gossip in the bar-room.”
    —Ralph Waldo Emerson (1803–1882)

    “It is time for dead languages to be quiet.”
    —Natalie Clifford Barney (1876–1972)