There is no exact definition for what a functional programming language is, but functional languages tend to emphasize a few key features. Among them are:
- First class functions: the ability to store and manipulate functions as if they were ordinary variables.
- Pure functions: functions which have so-called "side-effects," or consequences beyond simply returning an output.
- Declarative nature: functional languages tend to be declarative, meaning that instead of a program being a list of in-order instructions, a program is more often than not a graph of dependencies and definitions.
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