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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 Figure 2-9.

 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