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# <<(+Number1, +Number2, -Result)

Shifts Number1 left by Number2 bits and unifies the resulting value with Result.

Number1
  Integer.
Number2
  Integer.
Result
  Output: integer.

## Description

This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to <<(Number1, Number2, Result) is equivalent to

        Result is Number1 << Number2

which should be preferred for portability.

The shift behaves as if operating on an unlimited length two's complement representation. Shifting by a negative amount is the same as shifting by the same positive amount in the other direction.

In coroutining mode, if Number1 or Number2 are uninstantiated, the call to <</3 is delayed until these variables are instantiated.

### Modes and Determinism

- <<(+, +, -) is det

### Exceptions

(4) instantiation fault
  Number1 or Number2 is not instantiated (non-coroutining mode only).
(5) type error
  Number1 or Number2 is a number but not an integer.
(24) number expected
  Number1 or Number2 is not of a numeric type.

## Examples

    Success:
        Result is 1 << 3.		% gives Result = 8
        Result is 5 << 1.		% gives Result = 10

        Result is 10 << -1.		% gives Result = 5

        Result is -5 << 1.		% gives Result = -10

    Error:
        Result is 1.1 << 3.		% type error

## See Also

is / 2