length -package:bytestring -package:utf8-string -package:filepath -package:vector -package:unordered-containers package:relude

Returns the size/length of a finite structure as an Int. The default implementation just counts elements starting with the leftmost. Instances for structures that can compute the element count faster than via element-by-element counting, should provide a specialised implementation.

Examples

Basic usage:

>>> length []
0

>>> length ['a', 'b', 'c']
3

>>> length [1..]
* Hangs forever *

Returns the size/length of a finite structure as an Int.

Examples

Basic usage:

>>> bilength (True, 42)
2

>>> bilength (Right 42)
1

>>> bilength (BiList [1,2,3] [4,5])
5

>>> bilength (BiList [] [])
0

On infinite structures, this function hangs:

> bilength (BiList [1..] [])
* Hangs forever *

The genericLength function is an overloaded version of length. In particular, instead of returning an Int, it returns any type which is an instance of Num. It is, however, less efficient than length.

>>> genericLength [1, 2, 3] :: Int
3

>>> genericLength [1, 2, 3] :: Float
3.0

Users should take care to pick a return type that is wide enough to contain the full length of the list. If the width is insufficient, the overflow behaviour will depend on the (+) implementation in the selected Num instance. The following example overflows because the actual list length of 200 lies outside of the Int8 range of -128..127.

>>> genericLength [1..200] :: Int8
-56