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5.4.3 Number Read Syntax

The read syntax of any number is: [prefix…][sgn]data, where the optional sgn is one of the characters ‘-’ or ‘+’, data is the representation of the number, and prefix is zero or more of the following prefix strings:

#b
#B

Integers are described in binary,

#o
#O

Integers are in octal,

#d
#D

Integers are in decimal (the default),

#x
#X

Integers are in hexadecimal,

#e
#E

Coerce the number to an exact representation after parsing it,

#i
#I

Coerce to an inexact representation.

The representation of an integer is simply the digits representing that integer, in the radix chosen by any given prefix (defaults to decimal). Examples of valid integer read syntaxes for the number 42 could be ‘42’, ‘#x2a’, ‘#o52’, ‘#o+52’, …

The representation of a rational number is two sequences of digits, separated by a ‘/’ character. For example, ‘3/2’ represents the rational number three divided by two. It is supported without gmp too, but the read value is converted to float.

Inexact numbers are parsed from one of two representations: decimal point form, which is simply a decimal number containing a decimal point, and exponential form, which is a decimal number followed by the letter ‘e’ and a decimal exponent multiplying the first part of the number by that power of ten. For example, ‘10.0’, ‘10.’ and ‘1e1’ all read as the inexact number ten. Note that the radix prefixes currently have no effect when parsing inexact numbers, decimal is used exclusively.

An integer’s printed representation is simply the number printed in decimal with a preceding minus sign if it is negative. Rational numbers are printed as two integers separated by a ‘/’ character. Inexact numbers are printed in their decimal form.


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