length -package:unordered-containers package:base

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 *

Number of elements in NonEmpty list.

length returns the length of a finite list as an Int. It is an instance of the more general genericLength, the result type of which may be any kind of number.

>>> length []
0

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

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

Return the number of elements in an array, excluding the terminator

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

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 *

Compute the length of a NUL-terminated string. This address must refer to immutable memory. GHC includes a built-in rule for constant folding when the argument is a statically-known literal. That is, a core-to-core pass reduces the expression cstringLength# "hello"# to the constant 5#.