Eager evaluation

As explained in Functional Programming in JavaScript

Eager evaluation is an execution strategy that computes expressions or performs operations immediately rather than deferring them until their results are needed.

Eager evaluation computes an expression as soon as it is bound to a variable, even when no later operation needs its result. This can waste work when a large result is immediately reduced to a small subset. section 7.2

An unnecessary function call

In Maybe.of(student).getOrElse(createNewStudent()), JavaScript evaluates createNewStudent() before getOrElse decides whether it needs a fallback. A conditional avoids that call when student already exists. section 7.2

Figure 7.6. The composition of the function range (returns a list of numbers from beginning to end) with take (reads the first n elements). In eager evaluation, the range function executes completely, feeding its result to take. With lazy evaluation, the result of range never executes until the dependent operation, take, is called.

Compare eager range generation, which produces everything before take runs, with deferred generation that produces only the requested elements. section 7.2

Reduce eager-work costs by:

• Avoiding needless computations when a result may not be required. section 7.2

How Functional Programming in JavaScript covers it

How deep it goes

Defines immediate expression evaluation and contrasts it with deferred execution, without detailing language-runtime internals.

Examples

Uses range with take, a Maybe fallback, conditional control flow, and a Lodash map-filter-take chain.

What it assumes

Assumes basic JavaScript expressions, functions, variables, conditionals, and array-processing operations.

What you can do after

Apply conditional control flow or Lodash shortcut fusion to avoid unnecessary function calls and large intermediate results.

How it connects

Connects eager evaluation with lazy evaluation, the Maybe monad, functional combinators, and shortcut fusion.

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Also explained in

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  Deep Learning with R, Third EditionEager execution is an execution mode in which operations run immediately and produce results without first constructing a deferred computation graph.
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  Functional Programming in Scala, Second EditionStrict code evaluates an argument or expression before the surrounding computation proceeds, rather than delaying evaluation until its value is needed.
• 

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  Deep Learning with PyTorch, Second EditionAn execution model in which operations run immediately rather than being first built into a static graph.
• 

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  Fast Python: High performance techniques for large datasets

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Related concepts

• lazy evaluationcontrasts with · Lazy evaluation is an evaluation strategy that defers computing an expression or value until its result is needed, potentially avoiding the computation entirely.
• PyTorchused by · PyTorch is an open-source machine-learning framework for Python that provides tensor computation, automatic differentiation, and tools for building and training neural networks.
• applicative applyused by · Applicative apply is an operation that applies a function within an applicative context to a value within a compatible context while combining their effects.
• schedulingused by · Scheduling is the planning and coordination of when and in what order activities or computational work occur, potentially assigning them to available resources subject to constraints.
• code compilationcontrasts with · Code compilation is the translation of source code or another formal representation into an executable, intermediate, or lower-level representation.

This explainer was generated by Manning's knowledge graph from the text of Functional Programming in JavaScript. The section links point to the parts of the book it draws on.