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