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make unary minus part of number literals, refs #17020 (#17488)

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* make unary minus part of number literals, refs #17020
* fixes regression
This commit is contained in:
Andreas Rumpf
2021-03-24 09:47:11 +01:00
committed by GitHub
parent 465a41c308
commit 86af2f7b50
5 changed files with 173 additions and 39 deletions
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43
doc/manual.rst
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@@ -499,10 +499,11 @@ Numerical constants are of a single type and have the form::
hexdigit = digit | 'A'..'F' | 'a'..'f'
octdigit = '0'..'7'
bindigit = '0'..'1'
HEX_LIT = '0' ('x' | 'X' ) hexdigit ( ['_'] hexdigit )*
DEC_LIT = digit ( ['_'] digit )*
OCT_LIT = '0' 'o' octdigit ( ['_'] octdigit )*
BIN_LIT = '0' ('b' | 'B' ) bindigit ( ['_'] bindigit )*
unary_minus = '-' # See the section about unary minus
HEX_LIT = unary_minus? '0' ('x' | 'X' ) hexdigit ( ['_'] hexdigit )*
DEC_LIT = unary_minus? digit ( ['_'] digit )*
OCT_LIT = unary_minus? '0' 'o' octdigit ( ['_'] octdigit )*
BIN_LIT = unary_minus? '0' ('b' | 'B' ) bindigit ( ['_'] bindigit )*
INT_LIT = HEX_LIT
| DEC_LIT
@@ -521,7 +522,7 @@ Numerical constants are of a single type and have the form::
UINT64_LIT = INT_LIT ['\''] ('u' | 'U') '64'
exponent = ('e' | 'E' ) ['+' | '-'] digit ( ['_'] digit )*
FLOAT_LIT = digit (['_'] digit)* (('.' digit (['_'] digit)* [exponent]) |exponent)
FLOAT_LIT = unary_minus? digit (['_'] digit)* (('.' digit (['_'] digit)* [exponent]) |exponent)
FLOAT32_SUFFIX = ('f' | 'F') ['32']
FLOAT32_LIT = HEX_LIT '\'' FLOAT32_SUFFIX
| (FLOAT_LIT | DEC_LIT | OCT_LIT | BIN_LIT) ['\''] FLOAT32_SUFFIX
@@ -535,6 +536,38 @@ 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.
The fact that the unary minus `-` in a number literal like `-1` is considered
to be part of the literal is a late addition to the language. The rationale is that
an expression `-128'i8` should be valid and without this special case, this would
be impossible -- `128` is not a valid `int8` value, only `-128` is.
For the `unary_minus` rule there are further restrictions that are not covered
in the formal grammar. For `-` to be part of the number literal its immediately
preceeding character has to be in the
set `{' ', '\t', '\n', '\r', ',', ';', '(', '[', '{'}`. This set was designed to
cover most cases in a natural manner.
In the following examples, `-1` is a single token:
.. code-block:: nim
echo -1
echo(-1)
echo [-1]
echo 3,-1
"abc";-1
In the following examples, `-1` is parsed as two separate tokens (as `- 1`):
.. code-block:: nim
echo x-1
echo (int)-1
echo [a]-1
"abc"-1
There exists a literal for each numerical type that is
defined. The suffix starting with an apostrophe ('\'') is called a
`type suffix`:idx:. Literals without a type suffix are of an integer type