The Common Lisp answer is 0.3 and not 0.30000000000000004 because those are sing...

_19qg · on April 3, 2017

You can tell Common Lisp to read double-floats by default.

    CL-USER 113 > (+ 0.1 0.2)
    0.3

    CL-USER 114 > *read-default-float-format*
    SINGLE-FLOAT

    CL-USER 115 > (setf *read-default-float-format* 'double-float)
    DOUBLE-FLOAT

    CL-USER 116 > (+ 0.1 0.2)
    0.30000000000000005

Thus if one wants to make sure which float format Lisp should be reading,

a) specify the default format, as above

b) or use s, f, d, and l to specify the format (short float, single float, double-float, long-float). Example 1.0s0, 1.0f0, 1.0d0, 1.0l0