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Because generators compute their yielded values only on demand, they are useful for representing [[Stream (computing)|streams]], such as sequences that would be expensive or impossible to compute at once. These include e.g. infinite sequences and live data streams.
When eager evaluation is desirable (primarily when the sequence is finite, as otherwise evaluation will never terminate), one can either convert to a [[List (abstract data type)|list]], or use a parallel construction that creates a list instead of a generator. For example in Python a generator <code>g</code> can be evaluated to a list <code>l</code> via <code>l = list(g)</code>, while in F# the [[sequence expression]] <code>seq { ... }</code> evaluates lazily (a generator or sequence) but <code>[ ... ]</code> evaluates eagerly (a list).
In the presence of generators, loop constructs of a language – such as for and while – can be reduced into a single loop ... end loop construct; all the usual loop constructs can then be comfortably simulated by using suitable generators in the right way. For example, a ranged loop like <code>for x = 1 to 10</code> can be implemented as iteration through a generator, as in Python's <code>for x in range(10, 1)</code>. Further, <code>break</code> can be implemented as sending ''finish'' to the generator and then using <code>continue</code> in the loop.
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