Inf and NaN are numeric constants (with
typeof(.) "double"). In text input (e.g. in
scan and as.double), these are recognized
ignoring case as is infinity as an alternative to Inf.
NA_real_ and NA_integer_ are constants of
types "double" and "integer" representing missing
values. All other numeric constants start with a digit or period and
are either a decimal or hexadecimal constant optionally followed by
L.
Hexadecimal constants start with 0x or 0X followed by
a nonempty sequence from 0-9 a-f A-F . which is interpreted as a
hexadecimal number, optionally followed by a binary exponent. A binary
exponent consists of a P or p followed by an optional
plus or minus sign followed by a non-empty sequence of (decimal)
digits, and indicates multiplication by a power of two. Thus
0x123p456 is $291 * 2^456$.
Decimal constants consist of a nonempty sequence of digits possibly
containing a period (the decimal point), optionally followed by a
decimal exponent. A decimal exponent consists of an E or
e followed by an optional plus or minus sign followed by a
non-empty sequence of digits, and indicates multiplication by a power
of ten.
Values which are too large or too small to be representable will
overflow to Inf or underflow to 0.0.
A numeric constant immediately followed by i is regarded as an
imaginary complex number.
An numeric constant immediately followed by L is regarded as an
integer number when possible (and with a warning if it
contains a ".").
Only the ASCII digits 0--9 are recognized as digits, even in languages which have other representations of digits. The ‘decimal separator’ is always a period and never a comma.
Note that a leading plus or minus is not regarded by the parser as part of a numeric constant but as a unary operator applied to the constant.
Syntax. Quotes for the parsing of character constants,
2.1
typeof(2)
sqrt(1i) # remember elementary math?
utils::str(0xA0)
identical(1L, as.integer(1))
## You can combine the "0x" prefix with the "L" suffix :
identical(0xFL, as.integer(15))
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