In eager evaluation an expression is evaluated as soon as it gets bound to a variable. This is generally more efficient as a low-level strategy in simple programming languages, as it removes the need to build and managed intermediate data structures representing unevaluated expressions.
The low-level optimisation of forced eager evaluation prevents the higher-level optimisations and greater expressiveness that can be obtained from lazy evaluation in more sophisticated programming languages, which generally allow the implementation of both lazy and eager semantics.
See also: speculative execution[?].
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