Common Functions on Lists
Learn about the most important utility functions on lists.
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Before we dive deeper into writing functions on lists, let’s look at some of the most important predefined functions operating on lists. Here is a terminal running ghci, in which you can experiment with the various functions:
Checking length
The length function returns the number of elements in a list of any type.
Prelude> length [2, 4, 4, 1]
4
Prelude> length []
0
Checking list membership
The elem function checks whether a value is contained in a list at least once, and returns a boolean answer. It works on all lists whose element types can be compared with ==.
Prelude> elem 1 [9, 2, 1]
True
Prelude> elem 4 [9, 2, 1]
False
Prelude> 2 `elem` [9, 2, 1] -- use as operator
True