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# rational(+Number, -Result)

Converts Number into a rational number and unifies it with Result.
Number
A number.
Result
A variable or 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).
(5) type error
Result is a number but not of type rational.
(24) number expected
Number is not of a numeric type.
(24) number expected
Result is neither a number nor a variable.
(141) unimplemented functionality
Number is a bounded real

## Examples

```Success:
rational(25, 25_1).
rational(1.5, 3_2).
rational(3_4,3_4).
rational(9_12,3_4).
rational(-6, Result).      (gives Result = -6_1)
rational(0.1, Result).     (gives Result = 3602879701896397_36028797018963968)
Fail:
rational(1, 2_1).
Error:
rational(A, 1_3).                   (Error 4).
rational(3, 3).                     (Error 5).
rational(1, r).                     (Error 24).
rational(4 + 2, 6_1).               (Error 24).
rational(0.9__1.1, X).              (Error 141).

```