one of the atomic type specifiers short-float, single-float, double-float, or long-float, or else some other type specifier defined by the implementation to be acceptable.

The symbol single-float.

Controls the floating-point format that is to be used when reading a floating-point number that has no exponent marker or that has e or E for an exponent marker. Other exponent markers explicitly prescribe the floating-point format to be used.

The printer uses *read-default-float-format* to guide the choice of exponent markers when printing floating-point numbers.

 (let ((*read-default-float-format* 'double-float)) 
   (read-from-string "(1.0 1.0e0 1.0s0 1.0f0 1.0d0 1.0L0)")) 
→ (1.0   1.0   1.0   1.0 1.0   1.0)   ;Implementation has float format F. 
→ (1.0   1.0   1.0s0 1.0 1.0   1.0)   ;Implementation has float formats S and F. 
→ (1.0d0 1.0d0 1.0   1.0 1.0d0 1.0d0) ;Implementation has float formats F and D. 
→ (1.0d0 1.0d0 1.0s0 1.0 1.0d0 1.0d0) ;Implementation has float formats S, F, D. 
→ (1.0d0 1.0d0 1.0   1.0 1.0d0 1.0L0) ;Implementation has float formats F, D, L. 
→ (1.0d0 1.0d0 1.0s0 1.0 1.0d0 1.0L0) ;Implementation has formats S, F, D, L.