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.. _numeric-underscores:
Numeric underscores
-------------------
.. extension:: NumericUnderscores
:shortdesc: Enable support for :ref:`numeric underscores <numeric-underscores>`.
:since: 8.6.1
:status: Included in :extension:`GHC2021`
Allow the use of underscores in numeric literals.
GHC allows for numeric literals to be given in decimal, octal, hexadecimal,
binary, or float notation.
The language extension :extension:`NumericUnderscores` adds support for expressing
underscores in numeric literals.
For instance, the numeric literal ``1_000_000`` will be parsed into
``1000000`` when :extension:`NumericUnderscores` is enabled.
That is, underscores in numeric literals are ignored when
:extension:`NumericUnderscores` is enabled.
See also :ghc-ticket:`14473`.
For example:
.. code-block:: none
-- decimal
million = 1_000_000
billion = 1_000_000_000
lightspeed = 299_792_458
version = 8_04_1
date = 2017_12_31
-- hexadecimal
red_mask = 0xff_00_00
size1G = 0x3fff_ffff
-- binary
bit8th = 0b01_0000_0000
packbits = 0b1_11_01_0000_0_111
bigbits = 0b1100_1011__1110_1111__0101_0011
-- float
pi = 3.141_592_653_589_793
faraday = 96_485.332_89
avogadro = 6.022_140_857e+23
-- function
isUnderMillion = (< 1_000_000)
clip64M x
| x > 0x3ff_ffff = 0x3ff_ffff
| otherwise = x
test8bit x = (0b01_0000_0000 .&. x) /= 0
About validity:
.. code-block:: none
x0 = 1_000_000 -- valid
x1 = 1__000000 -- valid
x2 = 1000000_ -- invalid
x3 = _1000000 -- invalid
e0 = 0.0001 -- valid
e1 = 0.000_1 -- valid
e2 = 0_.0001 -- invalid
e3 = _0.0001 -- invalid
e4 = 0._0001 -- invalid
e5 = 0.0001_ -- invalid
f0 = 1e+23 -- valid
f1 = 1_e+23 -- valid
f2 = 1__e+23 -- valid
f3 = 1e_+23 -- invalid
g0 = 1e+23 -- valid
g1 = 1e+_23 -- invalid
g2 = 1e+23_ -- invalid
h0 = 0xffff -- valid
h1 = 0xff_ff -- valid
h2 = 0x_ffff -- valid
h3 = 0x__ffff -- valid
h4 = _0xffff -- invalid
|
