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# rational(+Number, -Result)

Converts Number into a rational number and unifies it with Result.
Number
A number.
Result
Output: rational number.

## Description

This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to rational(Number, Result) is equivalent to
```    Result is rational(Number)
```
which should be preferred.

When Number is an integer, Result is a rational with denominator 1.

When Number is already a rational, Result is identical to Number.

When Number is a float, Result is a rational whose value is exactly equal to the value of the floating-point number. Since floats are usually approximations of the intended value, the results may look unintuitive and have unnecessarily large numerators and denominators. Use rationalize/2 to produce the most compact rational that still converts back into the original float. rational/2 is usually faster than rationalize/2.

Bounded reals cannot be converted to rationals.

In coroutining mode, if Number is uninstantiated, the call to rational/2 is delayed until this variable is instantiated.

### Modes and Determinism

• rational(+, -) is det

### Exceptions

(4) instantiation fault
Number is not instantiated (non-coroutining mode only).
(24) number expected
Number is not of a numeric type.
(141) unimplemented functionality
Number is a bounded real

## Examples

```Success:
Result is rational(25).	% gives Result = 25_1
Result is rational(1.5).	% gives Result = 3_2
Result is rational(3_4).	% gives Result = 3_4
Result is rational(9_12).	% gives Result = 3_4
Result is rational(-6).	% gives Result = -6_1
Result is rational(0.1).    % gives Result = 3602879701896397_36028797018963968

Error:
Result is rational(0.9__1.1, X).     % unimplemented
```