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custom integer literals (#17489)

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* user defined integer literals; refs #17020
* updated renderer.nim
* use mlexerutils helper
* imported all test cases from https://github.com/nim-lang/Nim/pull/17020
* final grammar updated
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Andreas Rumpf 2021-03-24 14:46:19 +01:00 • committed by GitHub
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doc/manual.rst
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@ -490,11 +490,17 @@ this. Another reason is that Nim can thus support `array[char, int]` or
type is used for Unicode characters, it can represent any Unicode character.
`Rune` is declared in the `unicode module <unicode.html>`_.
A character literal that does not end in ``'`` interpreted as ``'`` if there
is a preceeding backtick token. There must be no whitespace between the preceeding
backtick token and the character literal. This special rule ensures that a declaration
like ``proc `'customLiteral`(s: string)`` is valid. See also
`Custom Numeric Literals <#custom-numeric-literals>`_.
Numerical constants
-------------------
Numerical constants are of a single type and have the form::
Numeric Literals
----------------
Numeric literals have the form::
hexdigit = digit | 'A'..'F' | 'a'..'f'
octdigit = '0'..'7'
@ -530,8 +536,10 @@ Numerical constants are of a single type and have the form::
FLOAT64_LIT = HEX_LIT '\'' FLOAT64_SUFFIX
| (FLOAT_LIT | DEC_LIT | OCT_LIT | BIN_LIT) ['\''] FLOAT64_SUFFIX
CUSTOM_NUMERIC_LIT = (FLOAT_LIT | DEC_LIT | OCT_LIT | BIN_LIT) '\'' CUSTOM_NUMERIC_SUFFIX
As can be seen in the productions, numerical constants can contain underscores
As can be seen in the productions, numeric literals can contain underscores
for readability. Integer and floating-point literals may be given in decimal (no
prefix), binary (prefix `0b`), octal (prefix `0o`), and hexadecimal
(prefix `0x`) notation.
@ -579,7 +587,7 @@ is optional if it is not ambiguous (only hexadecimal floating-point literals
with a type suffix can be ambiguous).
The type suffixes are:
The pre-defined type suffixes are:
================= =========================
Type Suffix Resulting type of literal
@ -611,6 +619,42 @@ the bit width of the datatype, it is accepted.
Hence: 0b10000000'u8 == 0x80'u8 == 128, but, 0b10000000'i8 == 0x80'i8 == -1
instead of causing an overflow error.
Custom Numeric Literals
~~~~~~~~~~~~~~~~~~~~~~~
If the suffix is not predefined, then the suffix is assumed to be a call
to a proc, template, macro or other callable identifier that is passed the
string containing the literal. The callable identifier needs to be declared
with a special ``'`` prefix:
.. code-block:: nim
import strutils
type u4 = distinct uint8 # a 4-bit unsigned integer aka "nibble"
proc `'u4`(n: string): u4 =
# The leading ' is required.
result = (parseInt(n) and 0x0F).u4
var x = 5'u4
More formally, a custom numeric literal `123'custom` is transformed
to r"123".`'custom` in the parsing step. There is no AST node kind that
corresponds to this transformation. The transformation naturally handles
the case that additional parameters are passed to the callee:
.. code-block:: nim
import strutils
type u4 = distinct uint8 # a 4-bit unsigned integer aka "nibble"
proc `'u4`(n: string; moreData: int): u4 =
result = (parseInt(n) and 0x0F).u4
var x = 5'u4(123)
Custom numeric literals are covered by the grammar rule named `CUSTOM_NUMERIC_LIT`.
Operators
---------