f(rational/1)

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- Packages

Availability:Arithmetic function (see is/2)

rational(+Expr)

Convert the Expr to a rational number or integer. The function returns the input on integers and rational numbers. For floating point numbers, the returned rational number exactly represents the float. As floats cannot exactly represent all decimal numbers the results may be surprising. In the examples below, doubles can represent 0.25 and the result is as expected, in contrast to the result of rational(0.1). The function rationalize/1 remedies this. See section 4.27.2.2 for more information on rational number support.

?- A is rational(0.25).

A is 1r4
?- A is rational(0.1).
A = 3602879701896397r36028797018963968

For every normal float X the relation X =:= rational(X) holds.

This function raises an evaluation_error(undefined) if Expr is NaN and evaluation_error(rational_overflow) if Expr is Inf.