Floats can be written in either decimal fraction or computerized
scientific notation: an optional sign, then a non-empty sequence of digits
with an embedded decimal point,
then an optional decimal exponent specification.
If there is no exponent specifier, then
the decimal point is required, and there must be digits
after it.
The exponent specifier consists of an exponent marker,
an optional sign, and a non-empty sequence of digits.
If no exponent specifier is present, or if the exponent marker e
(or E) is used, then
the format specified
by *read-default-float-format* is used.
See Figure~2–9.
An implementation may provide one or more kinds of float
that collectively make up the type float.
The letters s, f, d, and l (or their
respective uppercase equivalents) explicitly specify the
use of the types short-float, single-float,
double-float, and long-float, respectively.
The internal format used for an external representation depends only on the exponent marker, and not on the number of decimal digits in the external representation.
Figure 2–14 contains examples of notations for floats:
0.0 ;Floating-point zero in default format
0E0 ;As input, this is also floating-point zero in default format.
;As output, this would appear as 0.0.
0e0 ;As input, this is also floating-point zero in default format.
;As output, this would appear as 0.0.
-.0 ;As input, this might be a zero or a minus zero,
; depending on whether the implementation supports
; a distinct minus zero.
;As output, 0.0 is zero and -0.0 is minus zero.
0. ;On input, the integer zero—not a floating-point number!
;Whether this appears as 0 or 0. on output depends
;on the value of *print-radix*.
0.0s0 ;A floating-point zero in short format
0s0 ;As input, this is a floating-point zero in short format.
;As output, such a zero would appear as 0.0s0
; (or as 0.0 if short-float was the default format).
6.02E+23 ;Avogadro’s number, in default format
602E+21 ;Also Avogadro’s number, in default format
For information on how floats are printed, see Printing Floats.