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|NaN and Infinity floats and their syntax|
SWI-Prolog supports reading and printing‘special' floating point values according to Proposal for Prolog Standard core update wrt floating point arithmetic by Joachim Schimpf and available in ECLiPSe Prolog. In particular,
-1.0Inf. Any sequence matching the regular expression
[+-]?\sd+[.]\sd+Infis mapped to plus or minus infinity.
NaN(Not a Number) is printed as
1.xxxNaN, where 1.xxx is the float after replacing the exponent by‘1'. Such numbers are read, resulting in the same
NaNconstant can also be produced using the function nan/0, e.g.,
?- A is nan. A = 1.5NaN.
By default SWI-Prolog arithmetic (see section 4.26) follows the ISO standard with describes that floating point operations either produce a normal floating point number or raise an exception. section 18.104.22.168 describes the Prolog flags that can be used to support the IEEE special float values. The ability to create, read and write such values facilitates the exchange of data with languages that can represent the full range of IEEE doubles.