1 What is functional programming?
This chapter covers
- Understanding the benefits of functional programming
- Defining pure functions
- Referential transparency, purity, and the substitution model
Functional programming (FP) is based on a simple premise with far-reaching implications: we construct our programs using only pure functions —in other words, functions that have no side effects. But what are side effects? A function has a side effect if it does something other than simply return a result. This includes, for example, the following cases:
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Modifying a variable
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Modifying a data structure in place
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Setting a field on an object
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Throwing an exception or halting with an error
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Printing to the console or reading user input
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Reading from ...
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