What went wrong?
[1]> (log (exp 1))
0.99999994
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This is due to the finite precision of floating-point representations of fractional numbers.
Please see: http://en.wikipedia.org/wiki/Floating_point
(exp 1)is going to be an approximation ofe(which requires infinite precision to represent perfectly). The natural logarithm of that approximation will be approximately (but not exactly)1. Understanding floating-point representation will allow you to understand why this happens.CLISP is using your machine architecture’s native representation of floats. Most commonly by far, this representation is in one the formats specified by IEEE 754 (typically 32- or 64-bit; in your case it looks like 32-bit). In a nutshell, fractional parts are represented by a sum of inverse powers of 2 (i.e., some combination of
1/2,1/4,1/8, …1/2^32, etc.)