CLHS: Section 2.3.1

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## 2.3.1 Numbers as Tokens

When a token is read, it is interpreted as a number or symbol. The token is interpreted as a number if it satisfies the syntax for numbers specified in the next figure.

    numeric-token  ::=  integer |
    				   ratio   |
    				   float
    integer        ::=  [sign]
    				   decimal-digit+
    				   decimal-point |
    				   [sign]
    				   digit+
    ratio          ::=  [sign]
    				   {digit}+
    				   slash
    				   {digit}+
    float          ::=  [sign]
    				   {decimal-digit}*
    				   decimal-point
    				   {decimal-digit}+
    				   [exponent]
                        |
    				   [sign]
    				   {decimal-digit}+
    				   [decimal-point
    					   {decimal-digit}*]
    				   exponent
    exponent       ::=  exponent-marker
    				   [sign]
    				   {digit}+

    sign---a sign.
    slash---a slash
    decimal-point---a dot.
    exponent-marker---an exponent marker.
    decimal-digit---a digit in radix 10.
    digit---a digit in the current input radix.

Figure 2-9. Syntax for Numeric Tokens

## 2.3.1.1 Potential Numbers as Tokens

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