Doc needs help
The regular expression
[+-]?\sd+[.]\sd+Inf just can't be correct.
It should probably be (Perl regex; it is always good to specify which regex is being used as we of the IT guild have an embarrassment of riches in this domain):
...no mandatory spaces
\s, in fact spaces aren't even allowed.
-Inf is just a
- with a variable:
?- write(-Inf). -_1630 true.
Infinity is a signed float
?- A is -1.0Inf, float(A), A < 0. A = -1.0Inf. ?- A is +1.0Inf, float(A), A > 0. A = 1.0Inf.
An interesting edge case:
?- write(-0.0Inf). -1.0Inf true.
That doesn't look quite correct.
NaN is a float and also a number, but is not on the real line
Note that NaN is a float:
?- X is nan, float(X). X = 1.5NaN.
and a number:
?- X is nan, number(X). X = 1.5NaN.
But it incomparable, i.e. not anywhere on the (IEEE 754) real line:
?- X is nan, float(X), \+ (X < 0), \+ (X > 0), \+ (X =:= 0). X = 1.5NaN.
Arithmetic comparison between NaN also fails, but unification succeeds
?- X is nan, Y is nan, X = Y. X = Y, Y = 1.5NaN.
?- X is nan, Y is nan, X =:= Y. false.
What about "negative zero"
Seems to exist. 0.0 is the same as +0.0, but -0.0 is slightly different.
?- X1 is +0.0, X2 is -0.0, float(X1), float(X2), X1 =:= 0, X2 =:= 0, X1 =:= X2. X1 = 0.0, X2 = -0.0.
They don't unify:
?- X1 is +0.0, X2 is -0.0, X1 = X2. false.
They aren't equal either:
?- X1 is +0.0, X2 is -0.0, X1 == X2. false.
0.0 and +0.0 are exactly the same:
?- X1 is +0.0, X3 is 0.0, X1=X3, X1==X3, X1=:=X3. X1 = X3, X3 = 0.0.
?- X is -0.0, format("~f~n",[X]). -0.000000 X = -0.0. ?- X is +0.0, format("~f~n",[X]). 0.000000 X = 0.0. ?- X is nan, format("~f~n",[X]). nan X = 1.5NaN. ?- X is +1.0Inf, format("~f~n",[X]). inf X = 1.0Inf. ?- X is -1.0Inf, format("~f~n",[X]). -inf X = -1.0Inf.