comparing output from different implementations I've found the following (minor) bug:

 

I think there is a problem here as well:

Only SBCL gives the output I would expect, most implementations print ".0000" as ABCL does. From the HyperSpec 22.3.3.1: "If the parameter d is omitted, then there is no constraint on the number of digits to appear after the decimal point. A value is chosen for d in such a way that as many digits as possible may be printed subject to the width constraint imposed by the parameter w and the constraint that ___no trailing zero digits may appear in the fraction, except that if the fraction to be printed is zero, then a single zero digit should appear after the decimal point___ if permitted by the width constraint." This problem appears only when the value is close to zero, otherwise the output is fine:

> (format t "~5f" 1.00000001)

Regards,

Carlos Ungil